summaryrefslogtreecommitdiffstats
path: root/ast/dsbspecframe.c
blob: 20a8ed236f24bb924ca7ab96f7efa65f33e949cb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
/*
*class++
*  Name:
*     DSBSpecFrame

*  Purpose:
*     Dual sideband spectral coordinate system description.

*  Constructor Function:
c     astDSBSpecFrame
f     AST_DSBSPECFRAME

*  Description:
*     A DSBSpecFrame is a specialised form of SpecFrame which represents
*     positions in a spectrum obtained using a dual sideband instrument.
*     Such an instrument produces a spectrum in which each point contains
*     contributions from two distinctly different frequencies, one from
*     the "lower side band" (LSB) and one from the "upper side band" (USB).
*     Corresponding LSB and USB frequencies are connected by the fact
*     that they are an equal distance on either side of a fixed central
*     frequency known as the "Local Oscillator" (LO) frequency.
*
*     When quoting a position within such a spectrum, it is necessary to
*     indicate whether the quoted position is the USB position or the
*     corresponding LSB position. The SideBand attribute provides this
*     indication. Another option that the SideBand attribute provides is
*     to represent a spectral position by its topocentric offset from the
*     LO frequency.
*
*     In practice, the LO frequency is specified by giving the distance
*     from the LO frequency to some "central" spectral position. Typically
*     this central position is that of some interesting spectral feature.
*     The distance from this central position to the LO frequency is known
*     as the "intermediate frequency" (IF). The value supplied for IF can
*     be a signed value in order to indicate whether the LO frequency is
*     above or below the central position.

*  Inheritance:
*     The DSBSpecFrame class inherits from the SpecFrame class.

*  Attributes:
*     In addition to those attributes common to all SpecFrames, every
*     DSBSpecFrame also has the following attributes:
*
*     - AlignSideBand: Should alignment occur between sidebands?
*     - DSBCentre: The central position of interest.
*     - IF: The intermediate frequency used to define the LO frequency.
*     - ImagFreq: The image sideband equivalent of the rest frequency.
*     - SideBand: Indicates which sideband the DSBSpecFrame represents.

*  Functions:
c     The DSBSpecFrame class does not define any new functions beyond those
f     The DSBSpecFrame class does not define any new routines beyond those
*     which are applicable to all SpecFrames.

*  Copyright:
*     Copyright (C) 1997-2006 Council for the Central Laboratory of the
*     Research Councils

*  Licence:
*     This program is free software: you can redistribute it and/or
*     modify it under the terms of the GNU Lesser General Public
*     License as published by the Free Software Foundation, either
*     version 3 of the License, or (at your option) any later
*     version.
*
*     This program is distributed in the hope that it will be useful,
*     but WITHOUT ANY WARRANTY; without even the implied warranty of
*     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*     GNU Lesser General Public License for more details.
*
*     You should have received a copy of the GNU Lesser General
*     License along with this program.  If not, see
*     <http://www.gnu.org/licenses/>.

*  Authors:
*     DSB: David Berry (Starlink)

*  History:
*     5-AUG-2004 (DSB):
*        Original version.
*     7-OCT-2004 (DSB):
*        Fixed SetAttrib code which assigns values to SideBand. Previously
*        all supplied values were ignored, leaving SideBand unchanged.
*     2-SEP-2005 (DSB):
*        Allow conversion in any Domain within TopoMap (sometimes
*        SpecFrames have a new Domain set which is not equal to SPECTRUM").
*     12-SEP-2005 (DSB):
*        Set all attributes required to described the RestFreq value
*        before determining Mapping from RestFreq to ImagFreq in
*        GetImageFreq.
*     2-DEC-2005 (DSB):
*        Change default Domain from SPECTRUM to DSBSPECTRUM
*     3-APR-2006 (DSB):
*        Fix memory leak in astLoadDSBSpecFrame.
*     6-OCT-2006 (DSB):
*        Guard against annulling null pointers in subFrame.
*     27-OCT-2006 (DSB):
*        Added AlignSideBand attribute.
*     31-OCT-2006 (DSB):
*        Use AlignSideBand attribute in SubFrame only if we are not
*        currently restoring a FrameSet's integrity.
*     31-JAN-2007 (DSB):
*        Modified so that a DSBSpecFrame can be used as a template to find a
*        DSBSpecFrame (or SpecFrame) contained within a CmpFrame. This
*        involves changes in Match.
*     1-MAY-2007 (DSB):
*        The default for AlignSideband has been changed from 1 to 0.
*     8-MAY-2007 (DSB):
*        Correct initialisation of alignsideband in astInitDSBSpecFrame_.
*     19-OCT-2007 (DSB):
*        Ignore SideBand alignment if the AlignSideBand attribute is zero
*        in either the target or the template.
*     16-JAN-2007 (DSB):
*        Modify SubFrame so that DSBSpecFrames are aligned in the
*        observed sideband (LSB or USB) rather than always being aligned
*        in the USB.
*     12-FEB-2010 (DSB):
*        Report an error if the local oscillator frequency looks silly
*        (specifically, if it less than the absolute intermediate frequency).
*     29-APR-2011 (DSB):
*        Prevent astFindFrame from matching a subclass template against a
*        superclass target.
*class--

*  Implementation Deficiencies:
*     - The default values for System and StdOfRest inherited from the
*     SpecFrame class are "Wave" and "Heliocentric". These are not
*     usually what is wanted for a DSB instrument. Defaults such as
*     "Freq" and "Topo" may be more appropriate. However, changing the
*     defaults inherited from SpecFrame may cause problems in the
*     astConvert algorithm. The astConvertX function in frame.c includes
*     the following implementation deficiency warning: "One likely
*     problem is with attributes which default in both the source and
*     destination Frames. This means they also default in the common
*     coordinate system. If these default values were to differ when
*     matching different target Frames, however, we would be in trouble,
*     because the common coordinate system would not then be remaining
*     constant. The longer-term solution to this is probably to provide
*     some mechanism to "fix" all attribute values for a Frame, by taking
*     any attributes that are un-set and explicitly setting a firm value
*     (equal to the default) so they cannot then change". So the defaults
*     should probably be left unchanged until this fix is made.

*/

/* Module Macros. */
/* ============== */
/* Set the name of the class we are implementing. This indicates to
   the header files that define class interfaces that they should make
   "protected" symbols available. */
#define astCLASS DSBSpecFrame

#define BADSB -9999
#define FIRST_SB -1
#define LSB -1
#define LO  0
#define USB 1
#define LAST_SB 1

/* Include files. */
/* ============== */
/* Interface definitions. */
/* ---------------------- */

#include "globals.h"             /* Thread-safe global data access */
#include "error.h"               /* Error reporting facilities */
#include "memory.h"              /* Memory management facilities */
#include "object.h"              /* Base Object class */
#include "channel.h"             /* I/O channels */
#include "specframe.h"           /* Spectral frames (parent class) */
#include "unit.h"                /* Unit handling */
#include "cmpmap.h"              /* Compound Mappings */
#include "unitmap.h"             /* Unit Mappings */
#include "winmap.h"              /* Window Mappings */
#include "dsbspecframe.h"        /* Interface definition for this class */
#include "globals.h"             /* Thread-safe global data access */

/* Error code definitions. */
/* ----------------------- */
#include "ast_err.h"             /* AST error codes */

/* C header files. */
/* --------------- */
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>

/* Module Variables. */
/* ================= */

/* Address of this static variable is used as a unique identifier for
   member of this class. */
static int class_check;

/* Pointers to parent class methods which are extended by this class. */
static const char *(* parent_getattrib)( AstObject *, const char *, int * );
static const char *(* parent_getlabel)( AstFrame *, int, int * );
static int (* parent_match)( AstFrame *, AstFrame *, int, int **, int **, AstMapping **, AstFrame **, int * );
static int (* parent_subframe)( AstFrame *, AstFrame *, int, const int *, const int *, AstMapping **, AstFrame **, int * );
static int (* parent_testattrib)( AstObject *, const char *, int * );
static void (* parent_clearattrib)( AstObject *, const char *, int * );
static void (* parent_setattrib)( AstObject *, const char *, int * );
static void (* parent_overlay)( AstFrame *, const int *, AstFrame *, int * );
static const char *(* parent_getdomain)( AstFrame *, int * );

/* Define macros for accessing each item of thread specific global data. */
#ifdef THREAD_SAFE

/* Define how to initialise thread-specific globals. */
#define GLOBAL_inits \
   globals->Class_Init = 0; \
   globals->GetAttrib_Buff[ 0 ] = 0; \
   globals->GetLabel_Buff[ 0 ] = 0; \

/* Create the function that initialises global data for this module. */
astMAKE_INITGLOBALS(DSBSpecFrame)

/* Define macros for accessing each item of thread specific global data. */
#define class_init astGLOBAL(DSBSpecFrame,Class_Init)
#define class_vtab astGLOBAL(DSBSpecFrame,Class_Vtab)
#define getattrib_buff astGLOBAL(DSBSpecFrame,GetAttrib_Buff)
#define getlabel_buff astGLOBAL(DSBSpecFrame,GetLabel_Buff)



/* If thread safety is not needed, declare and initialise globals at static
   variables. */
#else

/* Define the thread-specific globals for this class. */

/* Buffer returned by GetAttrib. */
static char getattrib_buff[ 101 ];

/* Default Label string buffer */
static char getlabel_buff[ 101 ];


/* Define the class virtual function table and its initialisation flag
   as static variables. */
static AstDSBSpecFrameVtab class_vtab;   /* Virtual function table */
static int class_init = 0;       /* Virtual function table initialised? */

#endif

/* External Interface Function Prototypes. */
/* ======================================= */
/* The following functions have public prototypes only (i.e. no
   protected prototypes), so we must provide local prototypes for use
   within this module. */
AstDSBSpecFrame *astDSBSpecFrameId_( const char *, ... );

/* Prototypes for Private Member Functions. */
/* ======================================== */

static AstMapping *TopoMap( AstDSBSpecFrame *, int, const char *, int * );
static AstMapping *ToLOMapping( AstDSBSpecFrame *, const char *, int * )__attribute__((unused));
static AstMapping *ToLSBMapping( AstDSBSpecFrame *, const char *, int * );
static AstMapping *ToUSBMapping( AstDSBSpecFrame *, const char *, int * );
static const char *GetAttrib( AstObject *, const char *, int * );
static const char *GetLabel( AstFrame *, int, int * );
static double GetImagFreq( AstDSBSpecFrame *, int * );
static double GetLO( AstDSBSpecFrame *, const char *, const char *, int * );
static int Match( AstFrame *, AstFrame *, int, int **, int **, AstMapping **, AstFrame **, int * );
static int SubFrame( AstFrame *, AstFrame *, int, const int *, const int *, AstMapping **, AstFrame **, int * );
static int TestAttrib( AstObject *, const char *, int * );
static void ClearAttrib( AstObject *, const char *, int * );
static void Dump( AstObject *, AstChannel *, int * );
static void Overlay( AstFrame *, const int *, AstFrame *, int * );
static void SetAttrib( AstObject *, const char *, int * );
static void VerifyAttrs( AstDSBSpecFrame *, const char *, const char *, const char *, int * );
static const char *GetDomain( AstFrame *, int * );

static double GetIF( AstDSBSpecFrame *, int * );
static int TestIF( AstDSBSpecFrame *, int * );
static void ClearIF( AstDSBSpecFrame *, int * );
static void SetIF( AstDSBSpecFrame *, double, int * );

static double GetDSBCentre( AstDSBSpecFrame *, int * );
static int TestDSBCentre( AstDSBSpecFrame *, int * );
static void ClearDSBCentre( AstDSBSpecFrame *, int * );
static void SetDSBCentre( AstDSBSpecFrame *, double, int * );

static int GetSideBand( AstDSBSpecFrame *, int * );
static int TestSideBand( AstDSBSpecFrame *, int * );
static void ClearSideBand( AstDSBSpecFrame *, int * );
static void SetSideBand( AstDSBSpecFrame *, int, int * );

static int GetAlignSideBand( AstDSBSpecFrame *, int * );
static int TestAlignSideBand( AstDSBSpecFrame *, int * );
static void ClearAlignSideBand( AstDSBSpecFrame *, int * );
static void SetAlignSideBand( AstDSBSpecFrame *, int, int * );


/* Member functions. */
/* ================= */
static void ClearAttrib( AstObject *this_object, const char *attrib, int *status ) {
/*
*  Name:
*     ClearAttrib

*  Purpose:
*     Clear an attribute value for a DSBSpecFrame.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     void ClearAttrib( AstObject *this, const char *attrib, int *status )

*  Class Membership:
*     DSBSpecFrame member function (over-rides the astClearAttrib protected
*     method inherited from the SpecFrame class).

*  Description:
*     This function clears the value of a specified attribute for a
*     DSBSpecFrame, so that the default value will subsequently be used.

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame.
*     attrib
*        Pointer to a null-terminated string specifying the attribute
*        name.  This should be in lower case with no surrounding white
*        space.
*     status
*        Pointer to the inherited status variable.
*/

/* Local Variables: */
   AstDSBSpecFrame *this;        /* Pointer to the DSBSpecFrame structure */

/* Check the global error status. */
   if ( !astOK ) return;

/* Obtain a pointer to the DSBSpecFrame structure. */
   this = (AstDSBSpecFrame *) this_object;

/* Check the attribute name and clear the appropriate attribute. */

/* DSBCentre. */
/* ---------- */
   if ( !strcmp( attrib, "dsbcentre" ) ) {
      astClearDSBCentre( this );

/* IF */
/* -- */
   } else if ( !strcmp( attrib, "if" ) ) {
      astClearIF( this );

/* SideBand */
/* -------- */
   } else if ( !strcmp( attrib, "sideband" ) ) {
      astClearSideBand( this );

/* AlignSideBand */
/* ------------- */
   } else if ( !strcmp( attrib, "alignsideband" ) ) {
      astClearAlignSideBand( this );

/* Read-only attributes. */
/* --------------------- */
/* Test if the attribute name matches any of the read-only attributes
   of this class. If it does, then report an error. */
   } else if ( !strcmp( attrib, "imagfreq" ) ) {
      astError( AST__NOWRT, "astClear: Invalid attempt to clear the \"%s\" "
                "value for a %s.", status, attrib, astGetClass( this ) );
      astError( AST__NOWRT, "This is a read-only attribute." , status);

/* If the attribute is not recognised, pass it on to the parent method
   for further interpretation. */
   } else {
      (*parent_clearattrib)( this_object, attrib, status );
   }
}


static const char *GetAttrib( AstObject *this_object, const char *attrib, int *status ) {
/*
*  Name:
*     GetAttrib

*  Purpose:
*     Get the value of a specified attribute for a DSBSpecFrame.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     const char *GetAttrib( AstObject *this, const char *attrib, int *status )

*  Class Membership:
*     DSBSpecFrame member function (over-rides the protected astGetAttrib
*     method inherited from the SpecFrame class).

*  Description:
*     This function returns a pointer to the value of a specified
*     attribute for a DSBSpecFrame, formatted as a character string.

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame.
*     attrib
*        Pointer to a null-terminated string containing the name of
*        the attribute whose value is required. This name should be in
*        lower case, with all white space removed.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     - Pointer to a null-terminated string containing the attribute
*     value.

*  Notes:
*     - The returned string pointer may point at memory allocated
*     within the DSBSpecFrame, or at static memory. The contents of the
*     string may be over-written or the pointer may become invalid
*     following a further invocation of the same function or any
*     modification of the DSBSpecFrame. A copy of the string should
*     therefore be made if necessary.
*     - A NULL pointer will be returned if this function is invoked
*     with the global error status set, or if it should fail for any
*     reason.
*/

/* Local Variables: */
   astDECLARE_GLOBALS            /* Declare the thread specific global data */
   AstDSBSpecFrame *this;        /* Pointer to the DSBSpecFrame structure */
   AstMapping *tmap;             /* Ptr to Mapping from topofreq to this */
   const char *result;           /* Pointer value to return */
   double dval;                  /* Attribute value */
   double dtemp;                 /* Attribute value */
   int ival;                     /* Attribute value */

/* Initialise. */
   result = NULL;

/* Check the global error status. */
   if ( !astOK ) return result;

/* Get a pointer to the structure holding thread-specific global data. */
   astGET_GLOBALS(this_object);

/* Obtain a pointer to the SpecFrame structure. */
   this = (AstDSBSpecFrame *) this_object;

/* Compare "attrib" with each recognised attribute name in turn,
   obtaining the value of the required attribute. If necessary, write
   the value into "getattrib_buff" as a null-terminated string in an appropriate
   format.  Set "result" to point at the result string. */

/* DSBCentre */
/* --------- */
   if ( !strcmp( attrib, "dsbcentre" ) ) {

/* Get the value as topocentric frequency in Hz. */
      dval = astGetDSBCentre( this );

/* Find the Mapping from topocentric frequency in Hz to the spectral system
   described by this SpecFrame. */
      tmap = TopoMap( this, 0, "astGetAttrib", status );
      if ( astOK ) {

/* Transform the internal value from topocentric frequency into the required
   system. */
         astTran1( tmap, 1, &dval, 1, &dtemp );
         if( dtemp == AST__BAD ) {
            astError( AST__INTER, "astGetAttrib(%s): Cannot convert DSBCentre "
                      "value from topocentric frequency to the required "
                      "system.", status, astGetClass( this ) );
         } else {

/* Format it. */
            (void) sprintf( getattrib_buff, "%.*g", DBL_DIG, dtemp );
            result = getattrib_buff;
         }
         tmap = astAnnul( tmap );
      }

/* IF */
/* -- */
   } else if ( !strcmp( attrib, "if" ) ) {
      dval = astGetIF( this );
      if ( astOK ) {
         (void) sprintf( getattrib_buff, "%.*g", DBL_DIG, dval*1.0E-9 );
         result = getattrib_buff;
      }

/* ImagFreq */
/* -------- */
   } else if ( !strcmp( attrib, "imagfreq" ) ) {
      dval = astGetImagFreq( this );
      if ( astOK ) {
         (void) sprintf( getattrib_buff, "%.*g", DBL_DIG, dval*1.0E-9 );
         result = getattrib_buff;
      }

/* SideBand */
/* -------- */
   } else if ( !strcmp( attrib, "sideband" ) ) {
      ival = astGetSideBand( this );
      if ( astOK ) {
         result = ( ival == USB ) ? "USB" : (( ival == LO ) ? "LO" : "LSB" );
      }

/* AlignSideBand */
/* ------------- */
   } else if ( !strcmp( attrib, "alignsideband" ) ) {
      ival = astGetAlignSideBand( this ) ? 1 : 0;
      if ( astOK ) {
         (void) sprintf( getattrib_buff, "%d", ival );
         result = getattrib_buff;
      }

/* If the attribute name was not recognised, pass it on to the parent
   method for further interpretation. */
   } else {
      result = (*parent_getattrib)( this_object, attrib, status );
   }

/* Return the result. */
   return result;

}

static const char *GetDomain( AstFrame *this_frame, int *status ) {
/*
*  Name:
*     GetDomain

*  Purpose:
*     Obtain a pointer to the Domain attribute string for a DSBSpecFrame.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     const char *GetDomain( AstFrame *this, int *status )

*  Class Membership:
*     DSBSpecFrame member function (over-rides the astGetDomain protected
*     method inherited from the SpecFrame class).

*  Description:
*    This function returns a pointer to the Domain attribute string
*    for a DSBSpecFrame.

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     A pointer to a constant null-terminated string containing the
*     Domain value.

*  Notes:
*     - The returned pointer or the string it refers to may become
*     invalid following further invocation of this function or
*     modification of the DSBSpecFrame.
*     - A NULL pointer is returned if this function is invoked with
*     the global error status set or if it should fail for any reason.
*/

/* Local Variables: */
   AstDSBSpecFrame *this;        /* Pointer to DSBSpecFrame structure */
   const char *result;           /* Pointer value to return */

/* Initialise. */
   result = NULL;

/* Check the global error status. */
   if ( !astOK ) return result;

/* Obtain a pointer to the DSBSpecFrame structure. */
   this = (AstDSBSpecFrame *) this_frame;

/* If a Domain attribute string has been set, invoke the parent method
   to obtain a pointer to it. */
   if ( astTestDomain( this ) ) {
      result = (*parent_getdomain)( this_frame, status );

/* Otherwise, provide a pointer to a suitable default string. */
   } else {
      result = "DSBSPECTRUM";
   }

/* Return the result. */
   return result;
}

static double GetImagFreq( AstDSBSpecFrame *this, int *status ) {
/*
*+
*  Name:
*     astGetImagFreq

*  Purpose:
*     Get the value of the ImagFreq attribute.

*  Type:
*     Protected virtual function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     double GetImagFreq( AstDSBSpecFrame *this )

*  Class Membership:
*     DSBSpecFrame method.

*  Description:
*     This function returns the image sideband frequency corresponding to
*     the rest frequency.

*  Parameters:
*     this
*        Pointer to the Frame.

*  Returned Value:
*     The required frequency, in Hz.

*  Notes:
*     - A value of AST__BAD will be returned if this function is invoked
*     with the global error status set, or if it should fail for any
*     reason.
*-
*/

/* Local Variables: */
   AstDSBSpecFrame *rf_frame;/* DSBSpecFrame describing the rest frequency */
   AstMapping *map;          /* Pointer to "Observed to Image" mapping */
   double result;            /* The returned frequency */
   double rf;                /* Rest frequency in observed sideband */
   int sb;                   /* SideBand value */

/* Check the global error status. */
   if ( !astOK ) return AST__BAD;

/* The RestFreq attribute is an observed sideband frequency in the
   source's standard of rest, measured in Hz. Temporaily set attributes
   to these values. Create a copy of the supplied DSBSpecFrame and set
   its attributes to these values.  */
   rf_frame = astCopy( this );
   astSetStdOfRest( rf_frame, AST__SCSOR );
   astSetSystem( rf_frame, AST__FREQ );
   astSetUnit( rf_frame, 0, "Hz" );
   astSetC( rf_frame, "SideBand", "observed" );

/* Create a Mapping which transforms positions from the observed to the
   image sideband. */
   sb = astGetSideBand( rf_frame );
   if( sb == USB ) {
      map = ToLSBMapping( rf_frame, "astGetImagFreq", status );

   } else if( sb == LSB ) {
      map = ToUSBMapping( rf_frame, "astGetImagFreq", status );

   } else {
      map = NULL;
      astError( AST__INTER, "astGetImagFreq(%s): Illegal sideband value "
                "(%d) encountered (internal AST programming error).", status,
                astGetClass( this ), sb );
   }

/* Get the rest frequency in Hz, and transform it using the above Mapping. */
   rf = astGetRestFreq( rf_frame );
   astTran1( map, 1, &rf, 1, &result );

/* Free resources */
   map = astAnnul( map );
   rf_frame = astAnnul( rf_frame );

/* If an error has occurrred, return AST__BAD. */
   if( !astOK ) result = AST__BAD;

/* Return the result. */
   return result;

}

static const char *GetLabel( AstFrame *this, int axis, int *status ) {
/*
*  Name:
*     GetLabel

*  Purpose:
*     Access the Label string for a DSBSpecFrame axis.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     const char *GetLabel( AstFrame *this, int axis, int *status )

*  Class Membership:
*     DSBSpecFrame member function (over-rides the astGetLabel method inherited
*     from the SpecFrame class).

*  Description:
*     This function returns a pointer to the Label string for a specified axis
*     of a DSBSpecFrame.

*  Parameters:
*     this
*        Pointer to the SpecFrame.
*     axis
*        Axis index (zero-based) identifying the axis for which information is
*        required.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     Pointer to a constant null-terminated character string containing the
*     requested information.

*  Notes:
*     -  A NULL pointer will be returned if this function is invoked with the
*     global error status set, or if it should fail for any reason.
*/

/* Local Variables: */
   astDECLARE_GLOBALS            /* Declare the thread specific global data */
   const char *result;           /* Pointer to label string */

/* Check the global error status. */
   if ( !astOK ) return NULL;

/* Get a pointer to the structure holding thread-specific global data. */
   astGET_GLOBALS(this);

/* Initialise. */
   result = NULL;

/* Validate the axis index. */
   astValidateAxis( this, axis, 1, "astGetLabel" );

/* Invoke the parent astGetLabel method to obtain a pointer to it. */
   result = (*parent_getlabel)( this, axis, status );

/* Check if this is a default value. If so, append a string indicating
   the sideband. */
   if ( !astTestLabel( this, axis ) ) {

/* If OK, supply a pointer to a suitable default label string. */
      sprintf( getlabel_buff, "%s (%s)", result, astGetAttrib( this, "sideband" ) );
      result = getlabel_buff;
   }

/* Return the result. */
   return result;

}

static double GetLO( AstDSBSpecFrame *this, const char *check_msg,
                     const char *method, int *status ) {
/*
*  Name:
*     GetLO

*  Purpose:
*     Get the Local Oscillator frequency.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     double GetLO( AstDSBSpecFrame *this, const char *check_msg,
*                   const char *method, int *status )

*  Class Membership:
*     DSBSpecFrame method.

*  Description:
*     This function returns the local oscillator frequency in topocentric
*     frequency.

*  Parameters:
*     this
*        Pointer to the Frame.
*     check_msg
*        If not NULL, an error will be reported if either the DSBCentre
*        or IF attribute has not been set to an explicit value. In this
*        case, the error message will include the supplied text.
*     method
*        The name of the calling method - used in error messages.
*     status
*        Pointer to the inherited status value.

*  Returned Value:
*     The local oscillator frequency, in Hz.

*  Notes:
*     - An error is reported if the local oscillator frequency looks
*     un-physical (specifically, if it is less than the absolute value of
*     the intermediate frequency).
*     - A value of AST__BAD will be returned if this function is invoked
*     with the global error status set, or if it should fail for any
*     reason.
*-
*/

/* Local Variables: */
   double f_if;              /* Intermediate frequency (topo,HZ) */
   double result;            /* The returned frequency */

/* Check the global error status. */
   if ( !astOK ) return AST__BAD;

/* If required, check that explicit values have been assigned to the required
   attributes (i.e. report an error if a default value would be used for
   either attribute). */
   if( check_msg ) VerifyAttrs( this, check_msg, "IF DSBCentre", method,
                                status );

/* The local oscillator is the sum of the intermediate frequency and the
   observation centre frequency. */
   f_if = astGetIF( this );
   result = astGetDSBCentre( this ) + f_if;

/* Check the local  oscillator frequency is no smaller than the absolute
   intermediate frequency. */
   if( result < fabs( f_if ) && astOK ) {
      astError( AST__ATTIN, "%s(%s): The local oscillator frequency (%g Hz) "
                "is too low (less than the intermediate frequency: %g Hz).",
                status, method, astGetClass( this ), result, fabs( f_if ) );
      astError( AST__ATTIN, "   This could be caused by a bad value for"
                " either the IF attribute (currently %g Hz) or the DSBCentre "
                "attribute (currently %g Hz).", status, f_if,
                astGetDSBCentre( this ) );
   }

/* If an error has occurrred, return AST__BAD. */
   if( !astOK ) result = AST__BAD;

/* Return the result. */
   return result;
}

void astInitDSBSpecFrameVtab_(  AstDSBSpecFrameVtab *vtab, const char *name, int *status ) {
/*
*+
*  Name:
*     astInitDSBSpecFrameVtab

*  Purpose:
*     Initialise a virtual function table for a DSBSpecFrame.

*  Type:
*     Protected function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     void astInitDSBSpecFrameVtab( AstDSBSpecFrameVtab *vtab, const char *name )

*  Class Membership:
*     DSBSpecFrame vtab initialiser.

*  Description:
*     This function initialises the component of a virtual function
*     table which is used by the DSBSpecFrame class.

*  Parameters:
*     vtab
*        Pointer to the virtual function table. The components used by
*        all ancestral classes will be initialised if they have not already
*        been initialised.
*     name
*        Pointer to a constant null-terminated character string which contains
*        the name of the class to which the virtual function table belongs (it
*        is this pointer value that will subsequently be returned by the Object
*        astClass function).
*-
*/

/* Local Variables: */
   astDECLARE_GLOBALS            /* Pointer to thread-specific global data */
   AstObjectVtab *object;        /* Pointer to Object component of Vtab */
   AstFrameVtab *frame;          /* Pointer to Frame component of Vtab */

/* Check the local error status. */
   if ( !astOK ) return;

/* Get a pointer to the thread specific global data structure. */
   astGET_GLOBALS(NULL);

/* Initialize the component of the virtual function table used by the
   parent class. */
   astInitSpecFrameVtab( (AstSpecFrameVtab *) vtab, name );

/* Store a unique "magic" value in the virtual function table. This
   will be used (by astIsADSBSpecFrame) to determine if an object belongs
   to this class.  We can conveniently use the address of the (static)
   class_check variable to generate this unique value. */
   vtab->id.check = &class_check;
   vtab->id.parent = &(((AstSpecFrameVtab *) vtab)->id);

/* Initialise member function pointers. */
/* ------------------------------------ */
/* Store pointers to the member functions (implemented here) that provide
   virtual methods for this class. */
   vtab->ClearDSBCentre = ClearDSBCentre;
   vtab->TestDSBCentre = TestDSBCentre;
   vtab->GetDSBCentre = GetDSBCentre;
   vtab->SetDSBCentre = SetDSBCentre;

   vtab->ClearIF = ClearIF;
   vtab->TestIF = TestIF;
   vtab->GetIF = GetIF;
   vtab->SetIF = SetIF;

   vtab->ClearSideBand = ClearSideBand;
   vtab->TestSideBand = TestSideBand;
   vtab->GetSideBand = GetSideBand;
   vtab->SetSideBand = SetSideBand;

   vtab->ClearAlignSideBand = ClearAlignSideBand;
   vtab->TestAlignSideBand = TestAlignSideBand;
   vtab->GetAlignSideBand = GetAlignSideBand;
   vtab->SetAlignSideBand = SetAlignSideBand;

   vtab->GetImagFreq = GetImagFreq;

/* Save the inherited pointers to methods that will be extended, and
   replace them with pointers to the new member functions. */
   object = (AstObjectVtab *) vtab;
   frame = (AstFrameVtab *) vtab;

   parent_clearattrib = object->ClearAttrib;
   object->ClearAttrib = ClearAttrib;

   parent_getattrib = object->GetAttrib;
   object->GetAttrib = GetAttrib;

   parent_setattrib = object->SetAttrib;
   object->SetAttrib = SetAttrib;

   parent_testattrib = object->TestAttrib;
   object->TestAttrib = TestAttrib;

   parent_getdomain = frame->GetDomain;
   frame->GetDomain = GetDomain;

   parent_overlay = frame->Overlay;
   frame->Overlay = Overlay;

   parent_match = frame->Match;
   frame->Match = Match;

   parent_subframe = frame->SubFrame;
   frame->SubFrame = SubFrame;

   parent_getlabel = frame->GetLabel;
   frame->GetLabel = GetLabel;

/* Declare the class delete function.*/
   astSetDump( vtab, Dump, "DSBSpecFrame", "Dual sideband spectral axis" );

/* If we have just initialised the vtab for the current class, indicate
   that the vtab is now initialised, and store a pointer to the class
   identifier in the base "object" level of the vtab. */
   if( vtab == &class_vtab ) {
      class_init = 1;
      astSetVtabClassIdentifier( vtab, &(vtab->id) );
   }
}

static int Match( AstFrame *template_frame, AstFrame *target, int matchsub,
                  int **template_axes, int **target_axes, AstMapping **map,
                  AstFrame **result, int *status ) {
/*
*  Name:
*     Match

*  Purpose:
*     Determine if conversion is possible between two coordinate systems.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     int Match( AstFrame *template, AstFrame *target, int matchsub,
*                int **template_axes, int **target_axes,
*                AstMapping **map, AstFrame **result, int *status )

*  Class Membership:
*     DSBSpecFrame member function (over-rides the protected astMatch method
*     inherited from the SpecFrame class).

*  Description:
*     This function matches a "template" DSBSpecFrame to a "target" Frame and
*     determines whether it is possible to convert coordinates between them.
*     If it is, a mapping that performs the transformation is returned along
*     with a new Frame that describes the coordinate system that results when
*     this mapping is applied to the "target" coordinate system. In addition,
*     information is returned to allow the axes in this "result" Frame to be
*     associated with the corresponding axes in the "target" and "template"
*     Frames from which they are derived.

*  Parameters:
*     template
*        Pointer to the template DSBSpecFrame. This describes the coordinate
*        system (or set of possible coordinate systems) into which we wish to
*        convert our coordinates.
*     target
*        Pointer to the target Frame. This describes the coordinate system in
*        which we already have coordinates.
*     matchsub
*        If zero then a match only occurs if the template is of the same
*        class as the target, or of a more specialised class. If non-zero
*        then a match can occur even if this is not the case.
*     template_axes
*        Address of a location where a pointer to int will be returned if the
*        requested coordinate conversion is possible. This pointer will point
*        at a dynamically allocated array of integers with one element for each
*        axis of the "result" Frame (see below). It must be freed by the caller
*        (using astFree) when no longer required.
*
*        For each axis in the result Frame, the corresponding element of this
*        array will return the index of the template DSBSpecFrame axis from
*        which it is derived. If it is not derived from any template
*        DSBSpecFrame axis, a value of -1 will be returned instead.
*     target_axes
*        Address of a location where a pointer to int will be returned if the
*        requested coordinate conversion is possible. This pointer will point
*        at a dynamically allocated array of integers with one element for each
*        axis of the "result" Frame (see below). It must be freed by the caller
*        (using astFree) when no longer required.
*
*        For each axis in the result Frame, the corresponding element of this
*        array will return the index of the target Frame axis from which it
*        is derived. If it is not derived from any target Frame axis, a value
*        of -1 will be returned instead.
*     map
*        Address of a location where a pointer to a new Mapping will be
*        returned if the requested coordinate conversion is possible. If
*        returned, the forward transformation of this Mapping may be used to
*        convert coordinates between the "target" Frame and the "result"
*        Frame (see below) and the inverse transformation will convert in the
*        opposite direction.
*     result
*        Address of a location where a pointer to a new Frame will be returned
*        if the requested coordinate conversion is possible. If returned, this
*        Frame describes the coordinate system that results from applying the
*        returned Mapping (above) to the "target" coordinate system. In
*        general, this Frame will combine attributes from (and will therefore
*        be more specific than) both the target and the template Frames. In
*        particular, when the template allows the possibility of transformaing
*        to any one of a set of alternative coordinate systems, the "result"
*        Frame will indicate which of the alternatives was used.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     A non-zero value is returned if the requested coordinate conversion is
*     possible. Otherwise zero is returned (this will not in itself result in
*     an error condition).

*  Notes:
*     -  A value of zero will be returned if this function is invoked with the
*     global error status set, or if it should fail for any reason.

*  Implementation Notes:
*     This implementation addresses the matching of a DSBSpecFrame class
*     object to any other class of Frame. A DSBSpecFrame will match any class
*     of DSBSpecFrame (i.e. possibly from a derived class) but will not match
*     a less specialised class of Frame (except for a SpecFrame).
*/

/* Local Variables: */
   AstDSBSpecFrame *template;    /* Pointer to template DSBSpecFrame structure */
   AstFrame *frame0;             /* Pointer to Frame underlying axis 0 */
   int iaxis0;                   /* Axis index underlying axis 0 */
   int match;                    /* Coordinate conversion possible? */

/* Initialise the returned values. */
   *template_axes = NULL;
   *target_axes = NULL;
   *map = NULL;
   *result = NULL;
   match = 0;

/* Check the global error status. */
   if ( !astOK ) return match;

/* Obtain a pointer to the template DSBSpecFrame structure. */
   template = (AstDSBSpecFrame *) template_frame;

/* The first criterion for a match is that the template matches as a
   SpecFrame class object. This ensures that the number of axes (1) and
   domain, class, etc. of the target Frame are suitable. Invoke the parent
   "astMatch" method to verify this. */
   match = (*parent_match)( template_frame, target, matchsub,
                            template_axes, target_axes, map, result, status );

/* If a match was found, the target Frame must be (or contain) a SpecFrame,
   but this target SpecFrame may be a simple SpecFrame rather than a
   DSBSpecFrame. We use the returned objects directly if the target
   SpecFrame is not a DSBSpecFrame. So if a DSBSpecFrame and a base
   SpecFrame are aligned, this will result in the DSBSpecFrame behaving as
   a normal SpecFrame. */
   if ( astOK && match ) {

/* Get the primary Frame associated with the matching target axis. */
      astPrimaryFrame( target, (*target_axes)[ 0 ], &frame0, &iaxis0 );

/* Skip this next section, thus retaining the values returned by the
   parent Match method above, if the target axis is not a DSBSpecFrame. */
      if( astIsADSBSpecFrame( frame0 ) ) {

/* Annul the returned objects, which are not needed, but keep the axis
   association arrays which already hold the correct values. */
         *map = astAnnul( *map );
         *result = astAnnul( *result );

/* Use the target's "astSubFrame" method to create a new Frame (the
   result Frame) with a copy of of the target axis. This process also
   overlays the template attributes on to the target Frame and returns a
   Mapping between the target and result Frames which effects the required
   coordinate conversion. */
         match = astSubFrame( target, template, 1, *target_axes, *template_axes,
                              map, result );
      }

/* Free resources. */
      frame0 = astAnnul( frame0 );

   }

/* If an error occurred, or conversion to the result Frame's coordinate
   system was not possible, then free all memory, annul the returned
   objects, and reset the returned value. */
   if ( !astOK || !match ) {
      if( *template_axes ) *template_axes = astFree( *template_axes );
      if( *target_axes ) *target_axes = astFree( *target_axes );
      if( *map ) *map = astAnnul( *map );
      if( *result ) *result = astAnnul( *result );
      match = 0;
   }

/* Return the result. */
   return match;
}

static void Overlay( AstFrame *template, const int *template_axes,
                     AstFrame *result, int *status ) {
/*
*  Name:
*     Overlay

*  Purpose:
*     Overlay the attributes of a template DSBSpecFrame on to another Frame.

*  Type:
*     Private function.

*  Synopsis:
*     #include "specframe.h"
*     void Overlay( AstFrame *template, const int *template_axes,
*                   AstFrame *result, int *status )

*  Class Membership:
*     DSBSpecFrame member function (over-rides the protected astOverlay method
*     inherited from the SpecFrame class).

*  Description:
*     This function overlays attributes of a DSBSpecFrame (the "template") on to
*     another Frame, so as to over-ride selected attributes of that second
*     Frame. Normally only those attributes which have been specifically set
*     in the template will be transferred. This implements a form of
*     defaulting, in which a Frame acquires attributes from the template, but
*     retains its original attributes (as the default) if new values have not
*     previously been explicitly set in the template.
*
*     Note that if the result Frame is a DSBSpecFrame and a change of spectral
*     coordinate system occurs as a result of overlaying its System
*     attribute, then some of its original attribute values may no
*     longer be appropriate (e.g. the Title, or attributes describing
*     its axes). In this case, these will be cleared before overlaying
*     any new values.

*  Parameters:
*     template
*        Pointer to the template DSBSpecFrame, for which values should have been
*        explicitly set for any attribute which is to be transferred.
*     template_axes
*        Pointer to an array of int, with one element for each axis of the
*        "result" Frame (see below). For each axis in the result frame, the
*        corresponding element of this array should contain the (zero-based)
*        index of the template axis to which it corresponds. This array is used
*        to establish from which template axis any axis-dependent attributes
*        should be obtained.
*
*        If any axis in the result Frame is not associated with a template
*        axis, the corresponding element of this array should be set to -1.
*
*        If a NULL pointer is supplied, the template and result axis
*        indices are assumed to be identical.
*     result
*        Pointer to the Frame which is to receive the new attribute values.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     void

*  Notes:
*     -  In general, if the result Frame is not from the same class as the
*     template DSBSpecFrame, or from a class derived from it, then attributes may
*     exist in the template DSBSpecFrame which do not exist in the result Frame.
*     In this case, these attributes will not be transferred.
*/

/* Check the global error status. */
   if ( !astOK ) return;

/* Invoke the parent class astOverlay method to transfer attributes inherited
   from the parent class. */
   (*parent_overlay)( template, template_axes, result, status );

/* Check if the result Frame is a DSBSpecFrame or from a class derived from
   DSBSpecFrame. If not, we cannot transfer DSBSpecFrame attributes to it as it is
   insufficiently specialised. In this case simply omit these attributes. */
   if( astIsADSBSpecFrame( result ) && astOK ) {

/* Define macros that test whether an attribute is set in the template and,
   if so, transfers its value to the result. */
#define OVERLAY(attribute) \
   if ( astTest##attribute( template ) ) { \
      astSet##attribute( result, astGet##attribute( template ) ); \
   }

/* Use the macro to transfer each DSBSpecFrame attribute in turn. */
      OVERLAY(DSBCentre)
      OVERLAY(IF)
      OVERLAY(SideBand)
      OVERLAY(AlignSideBand)
   }

/* Undefine macros local to this function. */
#undef OVERLAY
}

static void SetAttrib( AstObject *this_object, const char *setting, int *status ) {
/*
*  Name:
*     SetAttrib

*  Purpose:
*     Set an attribute value for a DSBSpecFrame.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     void SetAttrib( AstObject *this, const char *setting )

*  Class Membership:
*     DSBSpecFrame member function (over-rides the astSetAttrib protected
*     method inherited from the SpecFrame class).

*  Description:
*     This function assigns an attribute value for a DSBSpecFrame, the
*     attribute and its value being specified by means of a string of
*     the form:
*
*        "attribute= value "
*
*     Here, "attribute" specifies the attribute name and should be in
*     lower case with no white space present. The value to the right
*     of the "=" should be a suitable textual representation of the
*     value to be assigned and this will be interpreted according to
*     the attribute's data type.  White space surrounding the value is
*     only significant for string attributes.

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame.
*     setting
*        Pointer to a null-terminated string specifying the new attribute
*        value.
*/

/* Local Variables: */
   AstDSBSpecFrame *this;        /* Pointer to the DSBSpecFrame structure */
   AstMapping *tmap;             /* Ptr to Mapping from this to topofreq */
   AstMapping *umap;             /* Ptr to Mapping between units */
   double dtemp;                 /* Attribute value */
   double dval;                  /* Attribute value */
   int ival;                     /* Attribute value */
   int len;                      /* Length of setting string */
   int nc;                       /* Used length */
   int off;                      /* Offset to start of string */

/* Check the global error status. */
   if ( !astOK ) return;

/* Obtain a pointer to the DSBSpecFrame structure. */
   this = (AstDSBSpecFrame *) this_object;

/* Obtain the length of the setting string. */
   len = (int) strlen( setting );

/* Test for each recognised attribute in turn, using "astSscanf" to parse the
   setting string and extract the attribute value (or an offset to it in the
   case of string values). In each case, use the value set in "nc" to check
   that the entire string was matched. Once a value has been obtained, use the
   appropriate method to set it. */

/* DSBCentre */
/* --------- */
   if ( strstr( setting, "dsbcentre=" ) ) {

/* Without any units indication - assume it is supplied in the system of
   the DSBSpecFrame. */
      int ok = 0;
      if( nc = 0,
           ( 1 == astSscanf( setting, "dsbcentre= %lg %n", &dval, &nc ) )
           && ( nc >= len ) ) {
         ok = 1;

/* With units indication. Is there a Mapping from the supplied units to the
   units used by the DSBSpecFrame? If so, use the Mapping to convert the
   supplied value to the required units. */
      } else if ( nc = 0,
           ( 1 == astSscanf( setting, "dsbcentre= %lg %n%*s %n", &dval, &off, &nc ) )
           && ( nc >= len ) ) {

         if( ( umap = astUnitMapper( setting + off, astGetUnit( this, 0 ), NULL, NULL ) ) ) {
            astTran1( umap, 1, &dval, 1, &dtemp );
            dval = dtemp;
            umap = astAnnul( umap );
            if( astOK && dval != AST__BAD ) ok = 1;

/* Otherwise report an error. */
         } else if( astOK ) {
            astError( AST__ATTIN, "astSetAttrib(%s): Value supplied for "
                      "attribute \"DSBCentre\" (%s) uses units which are "
                      "inappropriate for the current spectral system (%s).", status,
                       astGetClass( this ), setting + 10,
                       astGetTitle( this ) );
         }
      }

/* Convert the value from the supplied system to topocentric frequency in
   Hx, and store. */
      if( ok ) {

/* Find the Mapping from the spectral system described by this SpecFrame to
   topocentric frequency in Hz. */
         tmap = TopoMap( this, 1, "astSetAttrib", status );
         if ( astOK ) {

/* Transform the supplied value to topocentric frequency. */
            astTran1( tmap, 1, &dval, 1, &dtemp );
            if( dtemp == AST__BAD ) {
               astError( AST__ATTIN, "astSetAttrib(%s): The setting \"%s\" is "
                         "invalid for a %s.", status, astGetClass( this ), setting,
                         astGetClass( this ) );
            } else {

/* Store it. */
               astSetDSBCentre( this, dtemp );

            }
            tmap = astAnnul( tmap );
         }

      } else if( astOK ) {
         astError( AST__ATTIN, "astSetAttrib(%s): The setting \"%s\" is "
                   "invalid for a %s.", status, astGetClass( this ), setting,
                   astGetClass( this ) );
      }

/* IF */
/* -- */
/* Without any units indication - assume GHz. Convert to Hz for storage. */
   } else if ( nc = 0,
        ( 1 == astSscanf( setting, "if= %lg %n", &dval, &nc ) )
        && ( nc >= len ) ) {
      astSetIF( this, dval*1.0E9 );

/* With units indication. */
   } else if ( nc = 0,
        ( 1 == astSscanf( setting, "if= %lg %n%*s %n", &dval, &off, &nc ) )
        && ( nc >= len ) ) {

/* Is there a Mapping from the supplied units to Hz? If so, use the
   Mapping to convert the supplied value to Hz. */
      if( ( umap = astUnitMapper( setting + off, "Hz", NULL, NULL ) ) ) {
         astTran1( umap, 1, &dval, 1, &dtemp );
         umap = astAnnul( umap );

/* Set the intermediate frequency. */
         astSetIF( this, dtemp );

/* Otherwise report an error. */
      } else if( astOK ) {
         astError( AST__ATTIN, "astSetAttrib(%s): Intermediate frequency given "
                   "in an inappropriate system of units \"%g %s\".", status,
                   astGetClass( this ), dval, setting + off );
      }

/* SideBand */
/* -------- */
   } else if ( nc = 0,
               ( 0 == astSscanf( setting, "sideband= %n%*s %n", &ival, &nc ) )
               && ( nc >= len ) ) {

      if( astChrMatch( "usb", setting+ival ) ) {
         astSetSideBand( this, USB );

      } else if( astChrMatch( "lsb", setting+ival ) ) {
         astSetSideBand( this, LSB );

      } else if( astChrMatch( "lo", setting+ival ) ) {
         astSetSideBand( this, LO );

      } else if( astChrMatch( "observed", setting+ival ) ) {
         astSetSideBand( this, ( astGetIF( this ) > 0 ) ? LSB : USB );

      } else if( astChrMatch( "image", setting+ival ) ) {
         astSetSideBand( this, ( astGetIF( this ) <= 0 ) ? LSB : USB );

      } else {
         astError( AST__ATTIN, "astSetAttrib(%s): The setting \"%s\" is "
                   "invalid for a %s.", status, astGetClass( this ), setting,
                   astGetClass( this ) );
      }

/* AlignSideBand */
/* ------------- */
   } else if ( nc = 0,
        ( 1 == astSscanf( setting, "alignsideband= %d %n", &ival, &nc ) )
        && ( nc >= len ) ) {
      astSetAlignSideBand( this, ival );

/* Read-only attributes. */
/* --------------------- */
/* Define a macro to see if the setting string matches any of the
   read-only attributes of this class. */
#define MATCH(attrib) \
        ( nc = 0, ( 0 == astSscanf( setting, attrib "=%*[^\n]%n", &nc ) ) && \
                  ( nc >= len ) )

/* Use this macro to report an error if a read-only attribute has been
   specified. */
   } else if ( MATCH( "imagfreq" ) ) {
      astError( AST__NOWRT, "astSet: The setting \"%s\" is invalid for a %s.", status,
                setting, astGetClass( this ) );
      astError( AST__NOWRT, "This is a read-only attribute." , status);

/* Pass any unrecognised setting to the parent method for further
   interpretation. */
   } else {
      (*parent_setattrib)( this_object, setting, status );
   }
}

static int SubFrame( AstFrame *target_frame, AstFrame *template,
                     int result_naxes, const int *target_axes,
                     const int *template_axes, AstMapping **map,
                     AstFrame **result, int *status ) {
/*
*  Name:
*     SubFrame

*  Purpose:
*     Select axes from a DSBSpecFrame and convert to the new coordinate
*     system.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     int SubFrame( AstFrame *target, AstFrame *template,
*                   int result_naxes, const int *target_axes,
*                   const int *template_axes, AstMapping **map,
*                   AstFrame **result, int *status )

*  Class Membership:
*     DSBSpecFrame member function (over-rides the protected astSubFrame
*     method inherited from the SpecFrame class).

*  Description:
*     This function selects a requested sub-set (or super-set) of the axes
*     from a "target" DSBSpecFrame and creates a new Frame with copies of
*     the selected axes assembled in the requested order. It then
*     optionally overlays the attributes of a "template" Frame on to the
*     result. It returns both the resulting Frame and a Mapping that
*     describes how to convert between the coordinate systems described by
*     the target and result Frames. If necessary, this Mapping takes
*     account of any differences in the Frames' attributes due to the
*     influence of the template.

*  Parameters:
*     target
*        Pointer to the target DSBSpecFrame, from which axes are to be
*        selected.
*     template
*        Pointer to the template Frame, from which new attributes for the
*        result Frame are to be obtained. Optionally, this may be NULL, in
*        which case no overlaying of template attributes will be performed.
*     result_naxes
*        Number of axes to be selected from the target Frame. This number may
*        be greater than or less than the number of axes in this Frame (or
*        equal).
*     target_axes
*        Pointer to an array of int with result_naxes elements, giving a list
*        of the (zero-based) axis indices of the axes to be selected from the
*        target DSBSpecFrame. The order in which these are given determines
*        the order in which the axes appear in the result Frame. If any of the
*        values in this array is set to -1, the corresponding result axis will
*        not be derived from the target Frame, but will be assigned default
*        attributes instead.
*     template_axes
*        Pointer to an array of int with result_naxes elements. This should
*        contain a list of the template axes (given as zero-based axis indices)
*        with which the axes of the result Frame are to be associated. This
*        array determines which axes are used when overlaying axis-dependent
*        attributes of the template on to the result. If any element of this
*        array is set to -1, the corresponding result axis will not receive any
*        template attributes.
*
*        If the template argument is given as NULL, this array is not used and
*        a NULL pointer may also be supplied here.
*     map
*        Address of a location to receive a pointer to the returned Mapping.
*        The forward transformation of this Mapping will describe how to
*        convert coordinates from the coordinate system described by the target
*        DSBSpecFrame to that described by the result Frame. The inverse
*        transformation will convert in the opposite direction.
*     result
*        Address of a location to receive a pointer to the result Frame.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     A non-zero value is returned if coordinate conversion is possible
*     between the target and the result Frame. Otherwise zero is returned and
*     *map and *result are returned as NULL (but this will not in itself
*     result in an error condition). In general, coordinate conversion should
*     always be possible if no template Frame is supplied but may not always
*     be possible otherwise.

*  Notes:
*     -  A value of zero will be returned if this function is invoked with the
*     global error status set, or if it should fail for any reason.

*  Implementation Notes:
*     -  This implementation addresses the selection of axes from a
*     DSBSpecFrame object. This results in another object of the same class
*     only if the single DSBSpecFrame axis is selected exactly once.
*     Otherwise, the result is a Frame class object which inherits the
*     DSBSpecFrame's axis information (if appropriate) but none of the other
*     properties of a DSBSpecFrame.
*     -  In the event that a DSBSpecFrame results, the returned Mapping will
*     take proper account of the relationship between the target and result
*     coordinate systems.
*     -  In the event that a Frame class object results, the returned Mapping
*     will only represent a selection/permutation of axes.

*  Implementation Deficiencies:
*     -  Any axis selection is currently permitted. Probably this should be
*     restricted so that each axis can only be selected once. The
*     astValidateAxisSelection method will do this but currently there are bugs
*     in the CmpFrame class that cause axis selections which will not pass this
*     test. Install the validation when these are fixed.
*/

/* Local Variables: */
   AstDSBSpecFrame *dsbresult;/* Pointer to the DSBSpecFrame result Frame */
   AstDSBSpecFrame *dsbtarget;/* Pointer to the DSBSpecFrame target Frame */
   AstMapping *map1;          /* Intermediate Mapping */
   AstMapping *map2;          /* Intermediate Mapping */
   AstMapping *map3;          /* Intermediate Mapping */
   int alignsb;               /* Use sidebands to align the Frames? */
   int match;                 /* Coordinate conversion is possible? */
   int obs_sb;                /* The observed sideband value */
   int old_sb;                /* The original Sideband value */

/* Initialise the returned values. */
   *map = NULL;
   *result = NULL;
   match = 0;

/* Check the global error status. */
   if ( !astOK ) return match;

/* Invoke the astSubFrame method inherited from the parent SpecFrame
   class. This will (if possible) create a result Frame which is a
   DSBSpecFrame (since the supplied target Frame is a DSBSpecFrame).
   However, the Mapping from target to result Frame will take no account
   of any differences in the values of the attributes specific to the
   DSBSpecFrame class. */
   match = (*parent_subframe)( target_frame, template, result_naxes,
                               target_axes, template_axes, map, result, status );

/* If a match occurred, and the result and template Frames are both
   DSBSpecFrames, we now modify the Mapping to take account of
   DSBSpecFrame-specific attributes. */
   if( match && template && astIsADSBSpecFrame( template ) &&
                            astIsADSBSpecFrame( *result ) ) {

/* Get pointers to the two DSBSpecFrames */
      dsbtarget = (AstDSBSpecFrame *) target_frame;

/* See whether alignment occurs between sidebands. If the current call to
   this function is part of the process of restoring a FrameSet's integrity
   following changes to the FrameSet's current Frame, then we ignore the
   setting of the AlignSideBand attributes and use 1. This ensures that
   when the SideBand attribute (for instance) is changed via a FrameSet
   pointer, the Mappings within the FrameSet are modified to produce
   frequencies in the new SideBand. In most other cases, astronomers
   usually want to align the DSBSpecFrames as if they were basic SpecFrames
   (that is, ignoring the setting of the SideBand attribute). */
      if( astGetFrameFlags( target_frame ) & AST__INTFLAG ) {
         alignsb = 1;
      } else {
         alignsb = astGetAlignSideBand( dsbtarget ) &&
                   astGetAlignSideBand( (AstDSBSpecFrame *) template );
      }

/* If we are aligning the sidebands we need to modify the Mapping
   returned above by the parent SubFrame method. The existing Mapping
   will convert between the spectral systems represented by the two
   DSBSpecFrames but will not take account of any difference in
   sidebands. */
      if( alignsb ) {

/* We assume that alignment occurs in the observed sideband. Determine
   which side band is the observed sideband in the target. */
         old_sb = astGetSideBand( dsbtarget );
         astSetC( dsbtarget, "SideBand", "observed" );
         obs_sb = astGetSideBand( dsbtarget );
         astSetSideBand( dsbtarget, old_sb );

/* Create a Mapping which transforms positions from the target to an exact
   copy of the target in which the SideBand attribute is set to the
   observed (USB or LSB) sideband. This will be a UnitMap if the target
   already represents the observed sideband. */
         if( obs_sb == USB ) {
            map1 = ToUSBMapping( dsbtarget, "astSubFrame", status );

         } else if( obs_sb == LSB ) {
            map1 = ToLSBMapping( dsbtarget, "astSubFrame", status );

         } else {
            map1 = NULL;
            astError( AST__INTER, "astGetImagFreq(%s): Illegal sideband value "
                      "(%d) encountered (internal AST programming error).", status,
                      astGetClass( target_frame ), obs_sb );
         }

/* Determine which side band is the observed sideband in the result. */
         dsbresult = (AstDSBSpecFrame *) *result;
         old_sb = astGetSideBand( dsbresult );
         astSetC( dsbresult, "SideBand", "observed" );
         obs_sb = astGetSideBand( dsbresult );
         astSetSideBand( dsbresult, old_sb );

/* Create a Mapping which transforms positions from the result to an exact
   copy of the result in which the SideBand attribute is set to the
   obserfed sideband. This will be a UnitMap if the target already represents
   the observed sideband. */
         if( obs_sb == USB ) {
            map2 = ToUSBMapping( dsbresult, "astSubFrame", status );

         } else if( obs_sb == LSB ) {
            map2 = ToLSBMapping( dsbresult, "astSubFrame", status );

         } else {
            map2 = NULL;
            astError( AST__INTER, "astGetImagFreq(%s): Illegal sideband value "
                      "(%d) encountered (internal AST programming error).", status,
                      astGetClass( target_frame ), obs_sb );
         }

/* Invert it to get the mapping from the observed sideband to the result. */
         astInvert( map2 );

/* Form a Mapping which first maps target values to the observed sideband,
   then applies the Mapping returned by the parent SubFrame method in
   order to convert between spectral systems, and then converts from the
   observed sideband to the SideBand of the result. */
         map3 = (AstMapping *) astCmpMap( map1, *map, 1, "", status );
         map1 = astAnnul( map1 );
         *map = astAnnul( *map );
         map1 = (AstMapping *) astCmpMap( map3, map2, 1, "", status );
         map3 = astAnnul( map3 );
         map2 = astAnnul( map2 );

/* Returned the simplified Mapping. */
         *map = astSimplify( map1 );
         map1 = astAnnul( map1 );
      }
   }

/* If an error occurred or no match was found, annul the returned
   objects and reset the returned result. */
   if ( !astOK || !match ) {
      if( *map ) *map = astAnnul( *map );
      if( *result ) *result = astAnnul( *result );
      match = 0;
   }

/* Return the result. */
   return match;

}

static int TestAttrib( AstObject *this_object, const char *attrib, int *status ) {
/*
*  Name:
*     TestAttrib

*  Purpose:
*     Test if a specified attribute value is set for a DSBSpecFrame.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     int TestAttrib( AstObject *this, const char *attrib, int *status )

*  Class Membership:
*     DSBSpecFrame member function (over-rides the astTestAttrib protected
*     method inherited from the SpecFrame class).

*  Description:
*     This function returns a boolean result (0 or 1) to indicate whether
*     a value has been set for one of a DSBSpecFrame's attributes.

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame.
*     attrib
*        Pointer to a null-terminated string specifying the attribute
*        name.  This should be in lower case with no surrounding white
*        space.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     One if a value has been set, otherwise zero.

*  Notes:
*     - A value of zero will be returned if this function is invoked
*     with the global status set, or if it should fail for any reason.
*/

/* Local Variables: */
   AstDSBSpecFrame *this;        /* Pointer to the DSBSpecFrame structure */
   int result;                   /* Result value to return */

/* Initialise. */
   result = 0;

/* Check the global error status. */
   if ( !astOK ) return result;

/* Obtain a pointer to the DSBSpecFrame structure. */
   this = (AstDSBSpecFrame *) this_object;

/* Check the attribute name and test the appropriate attribute. */

/* DSBCentre */
/* --------- */
   if ( !strcmp( attrib, "dsbcentre" ) ) {
      result = astTestDSBCentre( this );

/* IF */
/* -- */
   } else if ( !strcmp( attrib, "if" ) ) {
      result = astTestIF( this );

/* SideBand */
/* -------- */
   } else if ( !strcmp( attrib, "sideband" ) ) {
      result = astTestSideBand( this );

/* AlignSideBand */
/* ------------- */
   } else if ( !strcmp( attrib, "alignsideband" ) ) {
      result = astTestAlignSideBand( this );

/* Read-only attributes. */
/* --------------------- */
/* Test if the attribute name matches any of the read-only attributes
   of this class. If it does, then return zero. */
   } else if ( !strcmp( attrib, "imagfreq" ) ) {
      result = 0;

/* If the attribute is not recognised, pass it on to the parent method
   for further interpretation. */
   } else {
      result = (*parent_testattrib)( this_object, attrib, status );
   }

/* Return the result, */
   return result;
}

static AstMapping *ToLOMapping( AstDSBSpecFrame *this, const char *method, int *status ){
/*
*  Name:
*     ToLOMapping

*  Purpose:
*     Create a Mapping which transforms a DSBSpecFrame to offset from the
*     local oscillator frequency.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     AstMapping *ToLOMapping( AstDSBSpecFrame *this, const char *method, int *status )

*  Class Membership:
*     DSBSpecFrame member function

*  Description:
*     This function returns a pointer to a new Mapping which transforms
*     positions in the supplied DSBSpecFrame into an offset from the local
*     oscillator frequency. This will be a UnitMap if the DSBSpecFrame
*     already represents offset from the local oscillator frequency.

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame.
*     method
*        Pointer to a null-terminated string containing the name of the
*        public invoking method. This is only used in the construction of
*        error messages.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     Pointer to a new Mapping.

*  Notes:
*     - A NULL pointer will be returned if this function is invoked
*     with the global error status set, or if it should fail for any
*     reason.
*/

/* Local Variables: */
   AstMapping *fmap;         /* LSB to USB (topo freq) */
   AstMapping *map1;         /* This to USB (topo freq) */
   AstMapping *map2;         /* This (LSB) to This (USB) */
   AstMapping *result;       /* Pointer to the returned Mapping */
   AstMapping *tmap;         /* This to topocentric freq */
   double f_lo;              /* Local oscillator freq (topo Hz) */
   double f_in_a;            /* First LSB or USB freq */
   double f_in_b;            /* Second LSB or USB freq */
   double f_out_a;           /* First LO freq */
   double f_out_b;           /* Second LO freq */
   int sb;                   /* SideBand value */

/* Initialise. */
   result = NULL;

/* Check the global error status. */
   if ( !astOK ) return result;

/* If the DSBSpecFrame already represents LO offset, return a UnitMap.*/
   sb = astGetSideBand( this );
   if( sb == LO ) {
      result = (AstMapping *) astUnitMap( 1, "", status );

/* If the DSBSpecFrame represents the USB or LSB, create a suitable WinMap. */
   } else {

/* Find the Mapping from the spectral system described by this SpecFrame to
   topocentric frequency in Hz. */
      tmap = TopoMap( this, 1, method, status );

/* Calculate the local oscillator frequency (topocentric in Hertz). */
      f_lo = GetLO( this, "create a Mapping to upper sideband",
                    "astGetImagFreq", status );

/* Create a 1D WinMap which converts f_in to f_out. */
      if( sb == LSB ) {
         f_in_a = 0.0;
         f_in_b = f_lo;
         f_out_a = f_lo;
         f_out_b = 0.0;
      } else {
         f_in_a = 0.0;
         f_in_b = -f_lo;
         f_out_a = f_lo;
         f_out_b = 0.0;
      }

      fmap = (AstMapping *) astWinMap( 1, &f_in_a, &f_in_b, &f_out_a, &f_out_b, "", status );

/* Construct the Mapping: input to f_in, f_in to f_out, f_out to input */
      map1 = (AstMapping *) astCmpMap( tmap, fmap, 1, "", status );
      astInvert( tmap );
      map2 = (AstMapping *) astCmpMap( map1, tmap, 1, "", status );

/* Simplify */
      result = astSimplify( map2 );

/* Free resources */
      tmap = astAnnul( tmap );
      fmap = astAnnul( fmap );
      map1 = astAnnul( map1 );
      map2 = astAnnul( map2 );
   }

/* Return NULL if an error has occurred. */
   if( !astOK ) result = astAnnul( result );

/* Return the result. */
   return result;

}

static AstMapping *ToLSBMapping( AstDSBSpecFrame *this, const char *method, int *status ){
/*
*  Name:
*     ToLSBMapping

*  Purpose:
*     Create a Mapping which transforms a DSBSpecFrame to the lower
*     sideband.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     AstMapping *ToLSBMapping( AstDSBSpecFrame *this, const char *method, int *status )

*  Class Membership:
*     DSBSpecFrame member function

*  Description:
*     This function returns a pointer to a new Mapping which transforms
*     positions in the supplied DSBSpecFrame to the lower sideband. This
*     will be a UnitMap if the DSBSpecFrame already represents the lower
*     sideband.

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame.
*     method
*        Pointer to a null-terminated string containing the name of the
*        public invoking method. This is only used in the construction of
*        error messages.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     Pointer to a new Mapping.

*  Notes:
*     - A NULL pointer will be returned if this function is invoked
*     with the global error status set, or if it should fail for any
*     reason.
*/

/* Local Variables: */
   AstMapping *fmap;         /* LSB to USB (topo freq) */
   AstMapping *map1;         /* This to USB (topo freq) */
   AstMapping *map2;         /* This (LSB) to This (USB) */
   AstMapping *result;       /* Pointer to the returned Mapping */
   AstMapping *tmap;         /* This to topocentric freq */
   double f_lo;              /* Local oscillator freq (topo Hz) */
   double f_out_a;           /* First LSB freq */
   double f_out_b;           /* Second LSB freq */
   double f_in_a;            /* First USB or LO freq */
   double f_in_b;            /* Second USB or LO freq */
   int sb;                   /* SideBand value */

/* Initialise. */
   result = NULL;

/* Check the global error status. */
   if ( !astOK ) return result;

/* If the DSBSpecFrame already represents the LSB, return a UnitMap.*/
   sb = astGetSideBand( this );
   if( sb == LSB ) {
      result = (AstMapping *) astUnitMap( 1, "", status );

/* If the DSBSpecFrame represents the USB or LO offset, create a suitable
   WinMap. */
   } else {

/* Find the Mapping from the spectral system described by this SpecFrame to
   topocentric frequency in Hz. */
      tmap = TopoMap( this, 1, method, status );

/* Calculate the local oscillator frequency (topocentric in Hertz). */
      f_lo = GetLO( this, "create a Mapping to lower sideband",
                    "astGetImagFreq", status );

/* Create a 1D WinMap which converts USB or LO to LSB. */
      if( sb == USB ) {
         f_in_a = 0.0;
         f_in_b = 2*f_lo;
         f_out_a = 2*f_lo;
         f_out_b = 0.0;
      } else {
         f_in_a = 0.0;
         f_in_b = f_lo;
         f_out_a = f_lo;
         f_out_b = 0.0;
      }

      fmap = (AstMapping *) astWinMap( 1, &f_in_a, &f_in_b, &f_out_a, &f_out_b, "", status );

/* Construct the Mapping: input to f_in, f_in to f_out, f_out to input */
      map1 = (AstMapping *) astCmpMap( tmap, fmap, 1, "", status );
      astInvert( tmap );
      map2 = (AstMapping *) astCmpMap( map1, tmap, 1, "", status );

/* Simplify */
      result = astSimplify( map2 );

/* Free resources */
      tmap = astAnnul( tmap );
      fmap = astAnnul( fmap );
      map1 = astAnnul( map1 );
      map2 = astAnnul( map2 );
   }

/* Return NULL if an error has occurred. */
   if( !astOK ) result = astAnnul( result );

/* Return the result. */
   return result;

}

static AstMapping *TopoMap( AstDSBSpecFrame *this, int forward,
                            const char *method, int *status ){
/*
*  Name:
*     TopoMap

*  Purpose:
*     Create a Mapping which transforms a DSBSpecFrame to topocentric
*     frequency.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     AstMapping *TopoMap( AstDSBSpecFrame *this, int forward,
*                          const char *method, int *status )

*  Class Membership:
*     DSBSpecFrame member function

*  Description:
*     This function returns a pointer to a new Mapping which transforms
*     positions in the supplied DSBSpecFrame to the corresponding
*     topocentric frequency values in Hz (or the inverse of this).

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame.
*     forward
*        If zero, the calcuated Mapping is inverted before being returned.
*     method
*        Pointer to a null-terminated string containing the name of the
*        public invoking method. This is only used in the construction of
*        error messages.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     Pointer to a new Mapping.

*  Notes:
*     - A NULL pointer will be returned if this function is invoked
*     with the global error status set, or if it should fail for any
*     reason.
*/

/* Local Variables: */
   AstMapping *result;       /* The returned Mapping */
   AstFrameSet *fs;          /* FrameSet connecting tf1 and tf2 */
   AstSpecFrame *tf1;        /* SpecFrame corresponding to this DSBSpecFrame */
   AstSpecFrame *tf2;        /* Topocentric frequency SpecFrame */
   int template_axis;        /* The axis to overlay */

/* Initialise. */
   result = NULL;

/* Check the global error status. */
   if ( !astOK ) return result;

/* Make a SpecFrame and then overlay the SpecFrame attributes of this
   DSBSpecFrame onto the new SpecFrame. This means it inherits the current
   values of things like ObsLon and ObsLat. */
   tf1 = astSpecFrame( "", status );
   template_axis = 0;
   (*parent_overlay)( (AstFrame *) this, &template_axis, (AstFrame *) tf1, status );

/* Copy this new SpecFrame and set its attributes to describe topocentric
   frequency in Hz. Ensure that alignment occurs in the topocentric Frame. */
   astSetAlignStdOfRest( tf1, AST__TPSOR);
   tf2 = astCopy( tf1 );
   astSetSystem( tf2, AST__FREQ );
   astSetStdOfRest( tf2, AST__TPSOR );
   astSetUnit( tf2, 0, "Hz" );

/* Find the Mapping from the spectral system described by this SpecFrame to
   topocentric frequency in Hz. */
   fs = astConvert( tf1, tf2, "" );
   if ( astOK ) {
      if( !fs ) {
         astError( AST__INTER, "%s(%s): Cannot convert DSBCentre "
                   "value from the supplied system to topocentric frequency "
                   "(internal AST programming error).", status, method,
                   astGetClass( this ) );
      } else {
         result = astGetMapping( fs, AST__BASE, AST__CURRENT );
         if( !forward ) astInvert( result );
      }
      fs = astAnnul( fs );
   }

/* Free resources */
   tf1 = astAnnul( tf1 );
   tf2 = astAnnul( tf2 );

/* Annul the result if an error has occurred. */
   if( !astOK ) result = astAnnul( result );

/* Return the result. */
   return result;

}

static AstMapping *ToUSBMapping( AstDSBSpecFrame *this, const char *method, int *status ){
/*
*  Name:
*     ToUSBMapping

*  Purpose:
*     Create a Mapping which transforms a DSBSpecFrame to the upper
*     sideband.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     AstMapping *ToUSBMapping( AstDSBSpecFrame *this, const char *method, int *status )

*  Class Membership:
*     DSBSpecFrame member function

*  Description:
*     This function returns a pointer to a new Mapping which transforms
*     positions in the supplied DSBSpecFrame to the upper sideband. This
*     will be a UnitMap if the DSBSpecFrame already represents the upper
*     sideband.

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame.
*     method
*        Pointer to a null-terminated string containing the name of the
*        public invoking method. This is only used in the construction of
*        error messages.
*     status
*        Pointer to the inherited status variable.

*  Returned Value:
*     Pointer to a new Mapping.

*  Notes:
*     - A NULL pointer will be returned if this function is invoked
*     with the global error status set, or if it should fail for any
*     reason.
*/

/* Local Variables: */
   AstMapping *fmap;         /* LSB to USB (topo freq) */
   AstMapping *map1;         /* This to USB (topo freq) */
   AstMapping *map2;         /* This (LSB) to This (USB) */
   AstMapping *result;       /* Pointer to the returned Mapping */
   AstMapping *tmap;         /* This to topocentric freq */
   double f_lo;              /* Local oscillator freq (topo Hz) */
   double f_in_a;            /* First LSB or LO freq */
   double f_in_b;            /* Second LSB or LO freq */
   double f_out_a;           /* First USB freq */
   double f_out_b;           /* Second USB freq */
   int sb;                   /* SideBand value */

/* Initialise. */
   result = NULL;

/* Check the global error status. */
   if ( !astOK ) return result;

/* If the DSBSpecFrame already represents the USB, return a UnitMap.*/
   sb = astGetSideBand( this );
   if( sb == USB ) {
      result = (AstMapping *) astUnitMap( 1, "", status );

/* If the DSBSpecFrame represents the LSB, or LO offset, create a suitable
   WinMap. */
   } else {

/* Find the Mapping from the spectral system described by this SpecFrame to
   topocentric frequency in Hz. */
      tmap = TopoMap( this, 1, method, status );

/* Calculate the local oscillator frequency (topocentric in Hertz). */
      f_lo = GetLO( this, "create a Mapping to upper sideband",
                    "astGetImagFreq", status );

/* Create a 1D WinMap which converts f_in to f_out. */
      if( sb == LSB ) {
         f_in_a = 0.0;
         f_in_b = 2*f_lo;
         f_out_a = 2*f_lo;
         f_out_b = 0.0;
      } else {
         f_in_a = 0.0;
         f_in_b = -f_lo;
         f_out_a = f_lo;
         f_out_b = 0.0;
      }

      fmap = (AstMapping *) astWinMap( 1, &f_in_a, &f_in_b, &f_out_a, &f_out_b, "", status );

/* Construct the Mapping: input to f_in, f_in to f_out, f_out to input */
      map1 = (AstMapping *) astCmpMap( tmap, fmap, 1, "", status );
      astInvert( tmap );
      map2 = (AstMapping *) astCmpMap( map1, tmap, 1, "", status );

/* Simplify */
      result = astSimplify( map2 );

/* Free resources */
      tmap = astAnnul( tmap );
      fmap = astAnnul( fmap );
      map1 = astAnnul( map1 );
      map2 = astAnnul( map2 );
   }

/* Return NULL if an error has occurred. */
   if( !astOK ) result = astAnnul( result );

/* Return the result. */
   return result;

}

static void VerifyAttrs( AstDSBSpecFrame *this, const char *purp,
                         const char *attrs, const char *method, int *status ) {
/*
*  Name:
*     VerifyAttrs

*  Purpose:
*     Verify that usable attribute values are available.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     void VerifyAttrs( AstDSBSpecFrame *this, const char *purp,
*                       const char *attrs, const char *method, int *status  )

*  Class Membership:
*     DSBSpecFrame member function

*  Description:
*     This function tests each attribute listed in "attrs". It returns
*     without action if 1) an explicit value has been set for each attribute
*     or 2) the UseDefs attribute of the supplied DSBSpecFrame is non-zero.
*
*     If UseDefs is zero (indicating that default values should not be
*     used for attributes), and any of the named attributes does not have
*     an explicitly set value, then an error is reported.

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame.
*     purp
*        Pointer to a text string containing a message which will be
*        included in any error report. This shouldindicate the purpose
*        for which the attribute value is required.
*     attrs
*        A string holding a space separated list of attribute names.
*     method
*        A string holding the name of the calling method for use in error
*        messages.
*     status
*        Pointer to the inherited status variable.

*/

/* Local Variables: */
   const char *a;
   const char *desc;
   const char *p;
   int len;
   int set;
   int state;

/* Check inherited status */
   if( !astOK ) return;

/* If the DSBSpecFrame has a non-zero value for its UseDefs attribute, then
   all attributes are assumed to have usable values, since the defaults
   will be used if no explicit value has been set. So we only need to do
   any checks if UseDefs is zero. */
   if( !astGetUseDefs( this ) ) {

/* Initialise variables to avoid compiler warnings. */
      a = NULL;
      desc = NULL;
      len = 0;
      set = 0;

/* Loop round the "attrs" string identifying the start and length of each
   non-blank word in the string. */
      state = 0;
      p = attrs;
      while( 1 ) {
         if( state == 0 ) {
            if( !isspace( *p ) ) {
               a = p;
               len = 1;
               state = 1;
            }
         } else {
            if( isspace( *p ) || !*p ) {

/* The end of a word has just been reached. Compare it to each known
   attribute value. Get a flag indicating if the attribute has a set
   value, and a string describing the attribute.*/
               if( len > 0 ) {

                  if( !strncmp( "DSBCentre", a, len ) ) {
                     set = astTestDSBCentre( this );
                     desc = "central position of interest";

                  } else if( !strncmp( "IF", a, len ) ) {
                     set = astTestIF( this );
                     desc = "intermediate frequency";

                  } else {
                     astError( AST__INTER, "VerifyAttrs(DSBSpecFrame): "
                               "Unknown attribute name \"%.*s\" supplied (AST "
                               "internal programming error).", status, len, a );
                  }

/* If the attribute does not have a set value, report an error. */
                  if( !set && astOK ) {
                     astError( AST__NOVAL, "%s(%s): Cannot %s.", status, method,
                               astGetClass( this ), purp );
                     astError( AST__NOVAL, "No value has been set for "
                               "the AST \"%.*s\" attribute (%s).", status, len, a,
                               desc );
                  }

/* Continue the word search algorithm. */
               }
               len = 0;
               state = 0;
            } else {
               len++;
            }
         }
         if( !*(p++) ) break;
      }
   }
}


/* Functions which access class attributes. */
/* ---------------------------------------- */
/* Implement member functions to access the attributes associated with
   this class using the macros defined for this purpose in the
   "object.h" file. For a description of each attribute, see the class
   interface (in the associated .h file). */

/*
*att++
*  Name:
*     ImagFreq

*  Purpose:
*     The image sideband equivalent of the rest frequency.

*  Type:
*     Public attribute.

*  Synopsis:
*     Floating point, read-only.

*  Description:
*     This is a read-only attribute giving the frequency which
*     corresponds to the rest frequency but is in the opposite sideband.

*     The value is calculated by first transforming the rest frequency
*     (given by the RestFreq attribute) from the standard of rest of the
*     source (given by the SourceVel and SourceVRF attributes) to the
*     standard of rest of the observer (i.e. the topocentric standard of
*     rest). The resulting topocentric frequency is assumed to be in the
*     same sideband as the value given for the DSBCentre attribute (the
*     "observed" sideband), and is transformed to the other sideband (the
*     "image" sideband). The new frequency is converted back to the standard
*     of rest of the source, and the resulting value is returned as the
*     attribute value, in units of GHz.

*  Applicability:
*     DSBSpecFrame
*        All DSBSpecFrames have this attribute.

*att--
*/


/*
*att++
*  Name:
*     DSBCentre

*  Purpose:
*     The central position of interest in a dual sideband spectrum.

*  Type:
*     Public attribute.

*  Synopsis:
*     Floating point.

*  Description:
*     This attribute specifies the central position of interest in a dual
*     sideband spectrum. Its sole use is to determine the local oscillator
*     frequency (the frequency which marks the boundary between the lower
*     and upper sidebands). See the description of the IF (intermediate
*     frequency) attribute for details of how the local oscillator frequency
*     is calculated. The sideband containing this central position is
*     referred to as the "observed" sideband, and the other sideband as
*     the "image" sideband.
*
*     The value is accessed as a position in the spectral system
*     represented by the SpecFrame attributes inherited by this class, but
*     is stored internally as topocentric frequency. Thus, if the System
*     attribute of the DSBSpecFrame is set to "VRAD", the Unit attribute
*     set to "m/s" and the StdOfRest attribute set to "LSRK", then values
*     for the DSBCentre attribute should be supplied as radio velocity in
*     units of "m/s" relative to the kinematic LSR (alternative units may
*     be used by appending a suitable units string to the end of the value).
*     This value is then converted to topocentric frequency and stored. If
*     (say) the Unit attribute is subsequently changed to "km/s" before
*     retrieving the current value of the DSBCentre attribute, the stored
*     topocentric frequency will be converted back to LSRK radio velocity,
*     this time in units of "km/s", before being returned.
*
*     The default value for this attribute is 30 GHz.

*  Applicability:
*     DSBSpecFrame
*        All DSBSpecFrames have this attribute.

*  Note:
*     - The attributes which define the transformation to or from topocentric
*     frequency should be assigned their correct values before accessing
*     this attribute. These potentially include System, Unit, StdOfRest,
*     ObsLon, ObsLat, ObsAlt, Epoch, RefRA, RefDec and RestFreq.

*att--
*/
/* The central frequency (topocentric frequency in Hz). */
astMAKE_CLEAR(DSBSpecFrame,DSBCentre,dsbcentre,AST__BAD)
astMAKE_GET(DSBSpecFrame,DSBCentre,double,3.0E10,((this->dsbcentre!=AST__BAD)?this->dsbcentre:3.0E10))
astMAKE_SET(DSBSpecFrame,DSBCentre,double,dsbcentre,value)
astMAKE_TEST(DSBSpecFrame,DSBCentre,( this->dsbcentre != AST__BAD ))


/*
*att++
*  Name:
*     IF

*  Purpose:
*     The intermediate frequency in a dual sideband spectrum.

*  Type:
*     Public attribute.

*  Synopsis:
*     Floating point.

*  Description:
*     This attribute specifies the (topocentric) intermediate frequency in
*     a dual sideband spectrum. Its sole use is to determine the local
*     oscillator (LO) frequency (the frequency which marks the boundary
*     between the lower and upper sidebands). The LO frequency is
*     equal to the sum of the centre frequency and the intermediate
*     frequency. Here, the "centre frequency" is the topocentric
*     frequency in Hz corresponding to the current value of the DSBCentre
*     attribute. The value of the IF attribute may be positive or
*     negative: a positive value results in the LO frequency being above
*     the central frequency, whilst a negative IF value results in the LO
*     frequency being below the central frequency. The sign of the IF
*     attribute value determines the default value for the SideBand
*     attribute.
*
*     When setting a new value for this attribute, the units in which the
*     frequency value is supplied may be indicated by appending a suitable
*     string to the end of the formatted value. If the units are not
*     specified, then the supplied value is assumed to be in units of GHz.
*     For instance, the following strings all result in an IF of 4 GHz being
*     used: "4.0", "4.0 GHz", "4.0E9 Hz", etc.
*
*     When getting the value of this attribute, the returned value is
*     always in units of GHz. The default value for this attribute is 4 GHz.

*  Applicability:
*     DSBSpecFrame
*        All DSBSpecFrames have this attribute.

*att--
*/
/* The intermediate frequency (topocentric in Hz). */
astMAKE_CLEAR(DSBSpecFrame,IF,ifr,AST__BAD)
astMAKE_GET(DSBSpecFrame,IF,double,4.0E9,((this->ifr!=AST__BAD)?this->ifr:4.0E9))
astMAKE_SET(DSBSpecFrame,IF,double,ifr,value)
astMAKE_TEST(DSBSpecFrame,IF,( this->ifr != AST__BAD ))

/*
*att++
*  Name:
*     SideBand

*  Purpose:
*     Indicates which sideband a dual sideband spectrum represents.

*  Type:
*     Public attribute.

*  Synopsis:
*     String.

*  Description:
*     This attribute indicates whether the DSBSpecFrame currently
*     represents its lower or upper sideband, or an offset from the local
*     oscillator frequency. When querying the current value, the returned
*     string is always one of "usb" (for upper sideband), "lsb" (for lower
*     sideband), or "lo" (for offset from the local oscillator frequency).
*     When setting a new value, any of the strings "lsb", "usb", "observed",
*     "image" or "lo" may be supplied (case insensitive). The "observed"
*     sideband is which ever sideband (upper or lower) contains the central
*     spectral position given by attribute DSBCentre, and the "image"
*     sideband is the other sideband. It is the sign of the IF attribute
*     which determines if the observed sideband is the upper or lower
*     sideband. The default value for SideBand is the observed sideband.

*  Applicability:
*     DSBSpecFrame
*        All DSBSpecFrames have this attribute.

*att--
*/
/* Protected access to the SideBand attribute uses BADSB to indicate
   "unset". Other negative values mean "LSB", zero means "LO" and
   positive values mean "USB". */
astMAKE_CLEAR(DSBSpecFrame,SideBand,sideband,BADSB)
astMAKE_SET(DSBSpecFrame,SideBand,int,sideband,((value<0)?LSB:((value==0)?LO:USB)))
astMAKE_TEST(DSBSpecFrame,SideBand,( this->sideband != BADSB ))
astMAKE_GET(DSBSpecFrame,SideBand,int,USB,(this->sideband == BADSB ? ((astGetIF( this )>0)?LSB:USB):this->sideband))

/*
*att++
*  Name:
*     AlignSideBand

*  Purpose:
*     Should the SideBand attribute be taken into account when aligning
*     this DSBSpecFrame with another DSBSpecFrame?

*  Type:
*     Public attribute.

*  Synopsis:
*     Integer (boolean).

*  Description:
*     This attribute controls how a DSBSpecFrame behaves when an attempt
*     is made to align it with another DSBSpecFrame using
c     astFindFrame or astConvert.
f     AST_FINDFRAME or AST_CONVERT.
*     If both DSBSpecFrames have a non-zero value for AlignSideBand, the
*     value of the SideBand attribute in each DSBSpecFrame is used so that
*     alignment occurs between sidebands. That is, if one DSBSpecFrame
*     represents USB and the other represents LSB then
c     astFindFrame and astConvert
f     AST_FINDFRAME and AST_CONVERT
*     will recognise that the DSBSpecFrames represent different sidebands
*     and will take this into account when constructing the Mapping that
*     maps positions in one DSBSpecFrame into the other. If AlignSideBand
*     in either DSBSpecFrame is set to zero, then the values of the SideBand
*     attributes are ignored. In the above example, this would result in a
*     frequency in the first DSBSpecFrame being mapped onto the same
*     frequency in the second DSBSpecFrame, even though those frequencies
*     refer to different sidebands. In other words, if either AlignSideBand
*     attribute is zero, then the two DSBSpecFrames aligns like basic
*     SpecFrames. The default value for AlignSideBand is zero.
*
c     When astFindFrame or astConvert
f     When AST_FINDFRAME or AST_CONVERT
*     is used on two DSBSpecFrames (potentially describing different spectral
*     coordinate systems and/or sidebands), it returns a Mapping which can be
*     used to transform a position in one DSBSpecFrame into the corresponding
*     position in the other. The Mapping is made up of the following steps in
*     the indicated order:
*
*     - If both DSBSpecFrames have a value of 1 for the AlignSideBand
*     attribute, map values from the target's current sideband (given by its
*     SideBand attribute) to the observed sideband (whether USB or LSB). If
*     the target already represents the observed sideband, this step will
*     leave the values unchanged. If either of the two DSBSpecFrames have a
*     value of zero for its AlignSideBand attribute, then this step is omitted.
*
*     - Map the values from the spectral system of the target to the spectral
*     system of the template. This Mapping takes into account all the
*     inherited SpecFrame attributes such as System, StdOfRest, Unit, etc.
*
*     - If both DSBSpecFrames have a value of 1 for the AlignSideBand
*     attribute, map values from the result's observed sideband to the
*     result's current sideband (given by its SideBand attribute). If the
*     result already represents the observed sideband, this step will leave
*     the values unchanged. If either of the two DSBSpecFrames have a value
*     of zero for its AlignSideBand attribute, then this step is omitted.

*  Applicability:
*     DSBSpecFrame
*        All DSBSpecFrames have this attribute.

*att--
*/
/* The AlignSideBand value has a value of -1 when not set yielding a
   default of 0. */
astMAKE_TEST(DSBSpecFrame,AlignSideBand,( this->alignsideband != -1 ))
astMAKE_CLEAR(DSBSpecFrame,AlignSideBand,alignsideband,-1)
astMAKE_GET(DSBSpecFrame,AlignSideBand,int,-1,((this->alignsideband==-1)?0:this->alignsideband) )
astMAKE_SET(DSBSpecFrame,AlignSideBand,int,alignsideband,(value?1:0))

/* Copy constructor. */
/* ----------------- */
/* None needed */

/* Destructor. */
/* ----------- */
/* None needed */

/* Dump function. */
/* -------------- */
static void Dump( AstObject *this_object, AstChannel *channel, int *status ) {
/*
*  Name:
*     Dump

*  Purpose:
*     Dump function for DSBSpecFrame objects.

*  Type:
*     Private function.

*  Synopsis:
*     void Dump( AstObject *this, AstChannel *channel, int *status )

*  Description:
*     This function implements the Dump function which writes out data
*     for the DSBSpecFrame class to an output Channel.

*  Parameters:
*     this
*        Pointer to the DSBSpecFrame whose data are being written.
*     channel
*        Pointer to the Channel to which the data are being written.
*     status
*        Pointer to the inherited status variable.
*/

/* Local Variables: */
   AstDSBSpecFrame *this;        /* Pointer to the DSBSpecFrame structure */
   const char *cval;             /* Attribute value */
   const char *comm;             /* Attribute comment */
   double dval;                  /* Attribute value */
   int ival;                     /* Attribute value */
   int set;                      /* Is attribute set? */

/* Check the global error status. */
   if ( !astOK ) return;

/* Obtain a pointer to the DSBSpecFrame structure. */
   this = (AstDSBSpecFrame *) this_object;

/* In the case of attributes, we first use the appropriate (private)
   Test...  member function to see if they are set. If so, we then use
   the (private) Get... function to obtain the value to be written
   out.

   For attributes which are not set, we use the astGet... method to
   obtain the value instead. This will supply a default value
   (possibly provided by a derived class which over-rides this method)
   which is more useful to a human reader as it corresponds to the
   actual default attribute value.  Since "set" will be zero, these
   values are for information only and will not be read back. */

/* DSBCentre */
/* --------- */
   set = TestDSBCentre( this, status );
   dval = set ? GetDSBCentre( this, status ) : astGetDSBCentre( this );
   astWriteDouble( channel, "DSBCen", set, 1, dval, "Central frequency (Hz topo)" );

/* IF */
/* -- */
   set = TestIF( this, status );
   dval = set ? GetIF( this, status ) : astGetIF( this );
   astWriteDouble( channel, "IF", set, 1, dval, "Intermediate frequency (Hz)" );

/* SideBand */
/* -------- */
   set = TestSideBand( this, status );
   ival = set ? GetSideBand( this, status ) : astGetSideBand( this );
   if( ival == LSB ) {
      cval = "LSB";
      comm = "Represents lower sideband";

   } else if( ival == LO ) {
      cval = "LO";
      comm = "Represents offset from LO frequency";

   } else {
      cval = "USB";
      comm = "Represents upper sideband";
   }
   astWriteString( channel, "SideBn", set, 1, cval, comm );

/* AlignSideBand */
/* ------------- */
   set = TestAlignSideBand( this, status );
   ival = set ? GetAlignSideBand( this, status ) : astGetAlignSideBand( this );
   astWriteInt( channel, "AlSdBn", set, 1, ival, "Align sidebands?" );
}

/* Standard class functions. */
/* ========================= */
/* Implement the astIsADSBSpecFrame and astCheckDSBSpecFrame functions using the macros
   defined for this purpose in the "object.h" header file. */
astMAKE_ISA(DSBSpecFrame,SpecFrame)
astMAKE_CHECK(DSBSpecFrame)

AstDSBSpecFrame *astDSBSpecFrame_( const char *options, int *status, ...) {
/*
*++
*  Name:
c     astDSBSpecFrame
f     AST_DSBSPECFRAME

*  Purpose:
*     Create a DSBSpecFrame.

*  Type:
*     Public function.

*  Synopsis:
c     #include "dsbspecframe.h"
c     AstDSBSpecFrame *astDSBSpecFrame( const char *options, ... )
f     RESULT = AST_DSBSPECFRAME( OPTIONS, STATUS )

*  Class Membership:
*     DSBSpecFrame constructor.

*  Description:
*     This function creates a new DSBSpecFrame and optionally initialises its
*     attributes.
*
*     A DSBSpecFrame is a specialised form of SpecFrame which represents
*     positions in a spectrum obtained using a dual sideband instrument.
*     Such an instrument produces a spectrum in which each point contains
*     contributions from two distinctly different frequencies, one from
*     the "lower side band" (LSB) and one from the "upper side band" (USB).
*     Corresponding LSB and USB frequencies are connected by the fact
*     that they are an equal distance on either side of a fixed central
*     frequency known as the "Local Oscillator" (LO) frequency.
*
*     When quoting a position within such a spectrum, it is necessary to
*     indicate whether the quoted position is the USB position or the
*     corresponding LSB position. The SideBand attribute provides this
*     indication. Another option that the SideBand attribute provides is
*     to represent a spectral position by its topocentric offset from the
*     LO frequency.
*
*     In practice, the LO frequency is specified by giving the distance
*     from the LO frequency to some "central" spectral position. Typically
*     this central position is that of some interesting spectral feature.
*     The distance from this central position to the LO frequency is known
*     as the "intermediate frequency" (IF). The value supplied for IF can
*     be a signed value in order to indicate whether the LO frequency is
*     above or below the central position.

*  Parameters:
c     options
f     OPTIONS = CHARACTER * ( * ) (Given)
c        Pointer to a null-terminated string containing an optional
c        comma-separated list of attribute assignments to be used for
c        initialising the new DSBSpecFrame. The syntax used is identical to
c        that for the astSet function and may include "printf" format
c        specifiers identified by "%" symbols in the normal way.
f        A character string containing an optional comma-separated
f        list of attribute assignments to be used for initialising the
f        new DSBSpecFrame. The syntax used is identical to that for the
f        AST_SET routine.
c     ...
c        If the "options" string contains "%" format specifiers, then
c        an optional list of additional arguments may follow it in
c        order to supply values to be substituted for these
c        specifiers. The rules for supplying these are identical to
c        those for the astSet function (and for the C "printf"
c        function).
f     STATUS = INTEGER (Given and Returned)
f        The global status.

*  Returned Value:
c     astDSBSpecFrame()
f     AST_DSBSPECFRAME = INTEGER
*        A pointer to the new DSBSpecFrame.

*  Notes:
*     - A null Object pointer (AST__NULL) will be returned if this
c     function is invoked with the AST error status set, or if it
f     function is invoked with STATUS set to an error value, or if it
*     should fail for any reason.
*--
*/

/* Local Variables: */
   astDECLARE_GLOBALS            /* Pointer to thread-specific global data */
   AstDSBSpecFrame *new;        /* Pointer to new DSBSpecFrame */
   va_list args;                /* Variable argument list */

/* Get a pointer to the thread specific global data structure. */
   astGET_GLOBALS(NULL);

/* Check the global status. */
   if ( !astOK ) return NULL;

/* Initialise the DSBSpecFrame, allocating memory and initialising the
   virtual function table as well if necessary. */
   new = astInitDSBSpecFrame( NULL, sizeof( AstDSBSpecFrame ), !class_init, &class_vtab,
                              "DSBSpecFrame" );

/* If successful, note that the virtual function table has been
   initialised. */
   if ( astOK ) {
      class_init = 1;

/* Obtain the variable argument list and pass it along with the options string
   to the astVSet method to initialise the new DSBSpecFrame's attributes. */
      va_start( args, status );
      astVSet( new, options, NULL, args );
      va_end( args );

/* If an error occurred, clean up by deleting the new object. */
      if ( !astOK ) new = astDelete( new );
   }

/* Return a pointer to the new DSBSpecFrame. */
   return new;
}

AstDSBSpecFrame *astDSBSpecFrameId_( const char *options, ... ) {
/*
*  Name:
*     astDSBSpecFrameId_

*  Purpose:
*     Create a DSBSpecFrame.

*  Type:
*     Private function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     AstDSBSpecFrame *astDSBSpecFrameId_( const char *options, ... )

*  Class Membership:
*     DSBSpecFrame constructor.

*  Description:
*     This function implements the external (public) interface to the
*     astDSBSpecFrame constructor function. It returns an ID value (instead
*     of a true C pointer) to external users, and must be provided
*     because astDSBSpecFrame_ has a variable argument list which cannot be
*     encapsulated in a macro (where this conversion would otherwise
*     occur).
*
*     The variable argument list also prevents this function from
*     invoking astDSBSpecFrame_ directly, so it must be a re-implementation
*     of it in all respects, except for the final conversion of the
*     result to an ID value.

*  Parameters:
*     As for astDSBSpecFrame_.

*  Returned Value:
*     The ID value associated with the new DSBSpecFrame.
*/

/* Local Variables: */
   astDECLARE_GLOBALS            /* Pointer to thread-specific global data */
   AstDSBSpecFrame *new;        /* Pointer to new DSBSpecFrame */
   va_list args;                /* Variable argument list */

   int *status;                  /* Pointer to inherited status value */

/* Get a pointer to the inherited status value. */
   status = astGetStatusPtr;

/* Get a pointer to the thread specific global data structure. */
   astGET_GLOBALS(NULL);

/* Check the global status. */
   if ( !astOK ) return NULL;

/* Initialise the DSBSpecFrame, allocating memory and initialising the
   virtual function table as well if necessary. */
   new = astInitDSBSpecFrame( NULL, sizeof( AstDSBSpecFrame ), !class_init, &class_vtab,
                              "DSBSpecFrame" );

/* If successful, note that the virtual function table has been
   initialised. */
   if ( astOK ) {
      class_init = 1;

/* Obtain the variable argument list and pass it along with the options string
   to the astVSet method to initialise the new DSBSpecFrame's attributes. */
      va_start( args, options );
      astVSet( new, options, NULL, args );
      va_end( args );

/* If an error occurred, clean up by deleting the new object. */
      if ( !astOK ) new = astDelete( new );
   }

/* Return an ID value for the new DSBSpecFrame. */
   return astMakeId( new );
}

AstDSBSpecFrame *astInitDSBSpecFrame_( void *mem, size_t size, int init,
                                       AstDSBSpecFrameVtab *vtab, const char *name, int *status ) {
/*
*+
*  Name:
*     astInitDSBSpecFrame

*  Purpose:
*     Initialise a DSBSpecFrame.

*  Type:
*     Protected function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     AstDSBSpecFrame *astInitDSBSpecFrame( void *mem, size_t size, int init,
*                               AstDSBSpecFrameVtab *vtab, const char *name )

*  Class Membership:
*     DSBSpecFrame initialiser.

*  Description:
*     This function is provided for use by class implementations to initialise
*     a new DSBSpecFrame object. It allocates memory (if necessary) to accommodate
*     the DSBSpecFrame plus any additional data associated with the derived class.
*     It then initialises a DSBSpecFrame structure at the start of this memory. If
*     the "init" flag is set, it also initialises the contents of a virtual
*     function table for a DSBSpecFrame at the start of the memory passed via the
*     "vtab" parameter.

*  Parameters:
*     mem
*        A pointer to the memory in which the DSBSpecFrame is to be initialised.
*        This must be of sufficient size to accommodate the DSBSpecFrame data
*        (sizeof(DSBSpecFrame)) plus any data used by the derived class. If a value
*        of NULL is given, this function will allocate the memory itself using
*        the "size" parameter to determine its size.
*     size
*        The amount of memory used by the DSBSpecFrame (plus derived class data).
*        This will be used to allocate memory if a value of NULL is given for
*        the "mem" parameter. This value is also stored in the DSBSpecFrame
*        structure, so a valid value must be supplied even if not required for
*        allocating memory.
*     init
*        A logical flag indicating if the DSBSpecFrame's virtual function table is
*        to be initialised. If this value is non-zero, the virtual function
*        table will be initialised by this function.
*     vtab
*        Pointer to the start of the virtual function table to be associated
*        with the new DSBSpecFrame.
*     name
*        Pointer to a constant null-terminated character string which contains
*        the name of the class to which the new object belongs (it is this
*        pointer value that will subsequently be returned by the astGetClass
*        method).

*  Returned Value:
*     A pointer to the new DSBSpecFrame.

*  Notes:
*     -  A null pointer will be returned if this function is invoked with the
*     global error status set, or if it should fail for any reason.
*-
*/

/* Local Variables: */
   AstDSBSpecFrame *new;        /* Pointer to new DSBSpecFrame */

/* Check the global status. */
   if ( !astOK ) return NULL;

/* If necessary, initialise the virtual function table. */
   if ( init ) astInitDSBSpecFrameVtab( vtab, name );

/* Initialise. */
   new = NULL;

/* Initialise a SpecFrame structure (the parent class) as the first component
   within the DSBSpecFrame structure, allocating memory if necessary. Specify that
   the SpecFrame should be defined in both the forward and inverse directions. */
   new = (AstDSBSpecFrame *) astInitSpecFrame( mem, size, 0,
                                       (AstSpecFrameVtab *) vtab, name );
   if ( astOK ) {

/* Initialise the DSBSpecFrame data. */
/* --------------------------------- */
      new->dsbcentre = AST__BAD;
      new->ifr = AST__BAD;
      new->sideband = BADSB;
      new->alignsideband = -1;

/* If an error occurred, clean up by deleting the new DSBSpecFrame. */
      if ( !astOK ) new = astDelete( new );
   }

/* Return a pointer to the new DSBSpecFrame. */
   return new;
}

AstDSBSpecFrame *astLoadDSBSpecFrame_( void *mem, size_t size,
                           AstDSBSpecFrameVtab *vtab, const char *name,
                           AstChannel *channel, int *status ) {
/*
*+
*  Name:
*     astLoadDSBSpecFrame

*  Purpose:
*     Load a DSBSpecFrame.

*  Type:
*     Protected function.

*  Synopsis:
*     #include "dsbspecframe.h"
*     AstDSBSpecFrame *astLoadDSBSpecFrame( void *mem, size_t size,
*                               AstDSBSpecFrameVtab *vtab, const char *name,
*                               AstChannel *channel )

*  Class Membership:
*     DSBSpecFrame loader.

*  Description:
*     This function is provided to load a new DSBSpecFrame using data read
*     from a Channel. It first loads the data used by the parent class
*     (which allocates memory if necessary) and then initialises a
*     DSBSpecFrame structure in this memory, using data read from the input
*     Channel.
*
*     If the "init" flag is set, it also initialises the contents of a
*     virtual function table for a DSBSpecFrame at the start of the memory
*     passed via the "vtab" parameter.


*  Parameters:
*     mem
*        A pointer to the memory into which the DSBSpecFrame is to be
*        loaded.  This must be of sufficient size to accommodate the
*        DSBSpecFrame data (sizeof(DSBSpecFrame)) plus any data used by derived
*        classes. If a value of NULL is given, this function will
*        allocate the memory itself using the "size" parameter to
*        determine its size.
*     size
*        The amount of memory used by the DSBSpecFrame (plus derived class
*        data).  This will be used to allocate memory if a value of
*        NULL is given for the "mem" parameter. This value is also
*        stored in the DSBSpecFrame structure, so a valid value must be
*        supplied even if not required for allocating memory.
*
*        If the "vtab" parameter is NULL, the "size" value is ignored
*        and sizeof(AstDSBSpecFrame) is used instead.
*     vtab
*        Pointer to the start of the virtual function table to be
*        associated with the new DSBSpecFrame. If this is NULL, a pointer
*        to the (static) virtual function table for the DSBSpecFrame class
*        is used instead.
*     name
*        Pointer to a constant null-terminated character string which
*        contains the name of the class to which the new object
*        belongs (it is this pointer value that will subsequently be
*        returned by the astGetClass method).
*
*        If the "vtab" parameter is NULL, the "name" value is ignored
*        and a pointer to the string "DSBSpecFrame" is used instead.

*  Returned Value:
*     A pointer to the new DSBSpecFrame.

*  Notes:
*     - A null pointer will be returned if this function is invoked
*     with the global error status set, or if it should fail for any
*     reason.
*-
*/

/* Local Constants. */
   astDECLARE_GLOBALS            /* Pointer to thread-specific global data */
#define KEY_LEN 50               /* Maximum length of a keyword */

/* Local Variables: */
   AstDSBSpecFrame *new;         /* Pointer to the new DSBSpecFrame */
   char *text;                   /* Pointer to string value */

/* Get a pointer to the thread specific global data structure. */
   astGET_GLOBALS(channel);

/* Initialise. */
   new = NULL;

/* Check the global error status. */
   if ( !astOK ) return new;

/* If a NULL virtual function table has been supplied, then this is
   the first loader to be invoked for this DSBSpecFrame. In this case the
   DSBSpecFrame belongs to this class, so supply appropriate values to be
   passed to the parent class loader (and its parent, etc.). */
   if ( !vtab ) {
      size = sizeof( AstDSBSpecFrame );
      vtab = &class_vtab;
      name = "DSBSpecFrame";

/* If required, initialise the virtual function table for this class. */
      if ( !class_init ) {
         astInitDSBSpecFrameVtab( vtab, name );
         class_init = 1;
      }
   }

/* Invoke the parent class loader to load data for all the ancestral
   classes of the current one, returning a pointer to the resulting
   partly-built DSBSpecFrame. */
   new = astLoadSpecFrame( mem, size, (AstSpecFrameVtab *) vtab, name,
                           channel );
   if ( astOK ) {

/* Read input data. */
/* ================ */
/* Request the input Channel to read all the input data appropriate to
   this class into the internal "values list". */
       astReadClassData( channel, "DSBSpecFrame" );

/* Now read each individual data item from this list and use it to
   initialise the appropriate instance variable(s) for this class. */

/* In the case of attributes, we first read the "raw" input value,
   supplying the "unset" value as the default. If a "set" value is
   obtained, we then use the appropriate (private) Set... member
   function to validate and set the value properly. */

/* DSBCentre */
/* --------- */
      new->dsbcentre = astReadDouble( channel, "dsbcen", AST__BAD );
      if ( TestDSBCentre( new, status ) ) SetDSBCentre( new, new->dsbcentre, status );

/* IF */
/* -- */
      new->ifr = astReadDouble( channel, "if", AST__BAD );
      if ( TestIF( new, status ) ) SetIF( new, new->ifr, status );

/* SideBand */
/* -------- */
      text = astReadString( channel, "sidebn", " " );
      if( astOK ) {
         if( !strcmp( text, " " ) ) {
            new->sideband = BADSB;
         } else if( !strcmp( text, "USB" ) ) {
            new->sideband = USB;
         } else if( !strcmp( text, "LSB" ) ) {
            new->sideband = LSB;
         } else if( !strcmp( text, "LO" ) ) {
            new->sideband = LO;
         } else {
            astError( AST__ATTIN, "astRead(%s): Invalid SideBand description "
                      "\"%s\".", status, astGetClass( channel ), text );
         }
         if ( TestSideBand( new, status ) ) SetSideBand( new, new->sideband, status );
         text = astFree( text );
      }

/* AlignSideBand */
/* ------------- */
      new->alignsideband = astReadInt( channel, "alsdbn", -1 );
      if( TestAlignSideBand( new, status ) ) SetAlignSideBand( new, new->alignsideband, status );

/* If an error occurred, clean up by deleting the new DSBSpecFrame. */
      if ( !astOK ) new = astDelete( new );
   }

/* Return the new DSBSpecFrame pointer. */
   return new;
}

/* Virtual function interfaces. */
/* ============================ */
/* These provide the external interface to the virtual functions defined by
   this class. Each simply checks the global error status and then locates and
   executes the appropriate member function, using the function pointer stored
   in the object's virtual function table (this pointer is located using the
   astMEMBER macro defined in "object.h").

   Note that the member function may not be the one defined here, as it may
   have been over-ridden by a derived class. However, it should still have the
   same interface. */

double astGetImagFreq_( AstDSBSpecFrame *this, int *status ) {
   if ( !astOK ) return AST__BAD;
   return (**astMEMBER(this,DSBSpecFrame,GetImagFreq))( this, status );
}