/*** File saoimage/wcslib/dsspos.c *** October 21, 1999 *** By Jessica Mink, jmink@cfa.harvard.edu *** Harvard-Smithsonian Center for Astrophysics *** Copyright (C) 1995-2002 *** Smithsonian Astrophysical Observatory, Cambridge, MA, USA This library 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 2 of the License, or (at your option) any later version. This library 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 Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Correspondence concerning WCSTools should be addressed as follows: Internet email: jmink@cfa.harvard.edu Postal address: Jessica Mink Smithsonian Astrophysical Observatory 60 Garden St. Cambridge, MA 02138 USA * Module: dsspos.c (Plate solution WCS conversion) * Purpose: Compute WCS from Digital Sky Survey plate fit * Subroutine: dsspos() converts from pixel location to RA,Dec * Subroutine: dsspix() converts from RA,Dec to pixel location These functions are based on the astrmcal.c portion of GETIMAGE by J. Doggett and the documentation distributed with the Digital Sky Survey. */ #include #include #include #include "wcs.h" int dsspos (xpix, ypix, wcs, xpos, ypos) /* Routine to determine accurate position for pixel coordinates */ /* returns 0 if successful otherwise 1 = angle too large for projection; */ /* based on amdpos() from getimage */ /* Input: */ double xpix; /* x pixel number (RA or long without rotation) */ double ypix; /* y pixel number (dec or lat without rotation) */ struct WorldCoor *wcs; /* WCS parameter structure */ /* Output: */ double *xpos; /* Right ascension or longitude in degrees */ double *ypos; /* Declination or latitude in degrees */ { double x, y, xmm, ymm, xmm2, ymm2, xmm3, ymm3, x2y2; double xi, xir, eta, etar, raoff, ra, dec; double cond2r = 1.745329252e-2; double cons2r = 206264.8062470964; double twopi = 6.28318530717959; double ctan, ccos; /* Ignore magnitude and color terms double mag = 0.0; double color = 0.0; */ /* Convert from image pixels to plate pixels */ x = xpix + wcs->x_pixel_offset - 1.0 + 0.5; y = ypix + wcs->y_pixel_offset - 1.0 + 0.5; /* Convert from pixels to millimeters */ xmm = (wcs->ppo_coeff[2] - x * wcs->x_pixel_size) / 1000.0; ymm = (y * wcs->y_pixel_size - wcs->ppo_coeff[5]) / 1000.0; xmm2 = xmm * xmm; ymm2 = ymm * ymm; xmm3 = xmm * xmm2; ymm3 = ymm * ymm2; x2y2 = xmm2 + ymm2; /* Compute coordinates from x,y and plate model */ xi = wcs->x_coeff[ 0]*xmm + wcs->x_coeff[ 1]*ymm + wcs->x_coeff[ 2] + wcs->x_coeff[ 3]*xmm2 + wcs->x_coeff[ 4]*xmm*ymm + wcs->x_coeff[ 5]*ymm2 + wcs->x_coeff[ 6]*(x2y2) + wcs->x_coeff[ 7]*xmm3 + wcs->x_coeff[ 8]*xmm2*ymm + wcs->x_coeff[ 9]*xmm*ymm2 + wcs->x_coeff[10]*ymm3 + wcs->x_coeff[11]*xmm*(x2y2) + wcs->x_coeff[12]*xmm*x2y2*x2y2; /* Ignore magnitude and color terms + wcs->x_coeff[13]*mag + wcs->x_coeff[14]*mag*mag + wcs->x_coeff[15]*mag*mag*mag + wcs->x_coeff[16]*mag*xmm + wcs->x_coeff[17]*mag*x2y2 + wcs->x_coeff[18]*mag*xmm*x2y2 + wcs->x_coeff[19]*color; */ eta = wcs->y_coeff[ 0]*ymm + wcs->y_coeff[ 1]*xmm + wcs->y_coeff[ 2] + wcs->y_coeff[ 3]*ymm2 + wcs->y_coeff[ 4]*xmm*ymm + wcs->y_coeff[ 5]*xmm2 + wcs->y_coeff[ 6]*(x2y2) + wcs->y_coeff[ 7]*ymm3 + wcs->y_coeff[ 8]*ymm2*xmm + wcs->y_coeff[ 9]*ymm*xmm2 + wcs->y_coeff[10]*xmm3 + wcs->y_coeff[11]*ymm*(x2y2) + wcs->y_coeff[12]*ymm*x2y2*x2y2; /* Ignore magnitude and color terms + wcs->y_coeff[13]*mag + wcs->y_coeff[14]*mag*mag + wcs->y_coeff[15]*mag*mag*mag + wcs->y_coeff[16]*mag*ymm + wcs->y_coeff[17]*mag*x2y2) + wcs->y_coeff[18]*mag*ymm*x2y2 + wcs->y_coeff[19]*color; */ /* Convert to radians */ xir = xi / cons2r; etar = eta / cons2r; /* Convert to RA and Dec */ ctan = tan (wcs->plate_dec); ccos = cos (wcs->plate_dec); raoff = atan2 (xir / ccos, 1.0 - etar * ctan); ra = raoff + wcs->plate_ra; if (ra < 0.0) ra = ra + twopi; *xpos = ra / cond2r; dec = atan (cos (raoff) * ((etar + ctan) / (1.0 - (etar * ctan)))); *ypos = dec / cond2r; return 0; } int dsspix (xpos, ypos, wcs, xpix, ypix) /* Routine to determine pixel coordinates for sky position */ /* returns 0 if successful otherwise 1 = angle too large for projection; */ /* based on amdinv() from getimage */ /* Input: */ double xpos; /* Right ascension or longitude in degrees */ double ypos; /* Declination or latitude in degrees */ struct WorldCoor *wcs; /* WCS parameter structure */ /* Output: */ double *xpix; /* x pixel number (RA or long without rotation) */ double *ypix; /* y pixel number (dec or lat without rotation) */ { double div,xi,eta,x,y,xy,x2,y2,x2y,y2x,x3,y3,x4,y4,x2y2,cjunk,dx,dy; double sypos,cypos,syplate,cyplate,sxdiff,cxdiff; double f,fx,fy,g,gx,gy, xmm, ymm; double conr2s = 206264.8062470964; double tolerance = 0.0000005; int max_iterations = 50; int i; double xr, yr; /* position in radians */ *xpix = 0.0; *ypix = 0.0; /* Convert RA and Dec in radians to standard coordinates on a plate */ xr = degrad (xpos); yr = degrad (ypos); sypos = sin (yr); cypos = cos (yr); if (wcs->plate_dec == 0.0) wcs->plate_dec = degrad (wcs->yref); syplate = sin (wcs->plate_dec); cyplate = cos (wcs->plate_dec); if (wcs->plate_ra == 0.0) wcs->plate_ra = degrad (wcs->yref); sxdiff = sin (xr - wcs->plate_ra); cxdiff = cos (xr - wcs->plate_ra); div = (sypos * syplate) + (cypos * cyplate * cxdiff); if (div == 0.0) return (1); xi = cypos * sxdiff * conr2s / div; eta = ((sypos * cyplate) - (cypos * syplate * cxdiff)) * conr2s / div; /* Set initial value for x,y */ if (wcs->plate_scale == 0.0) return (1); xmm = xi / wcs->plate_scale; ymm = eta / wcs->plate_scale; /* Iterate by Newton's method */ for (i = 0; i < max_iterations; i++) { /* X plate model */ xy = xmm * ymm; x2 = xmm * xmm; y2 = ymm * ymm; x2y = x2 * ymm; y2x = y2 * xmm; x2y2 = x2 + y2; cjunk = x2y2 * x2y2; x3 = x2 * xmm; y3 = y2 * ymm; x4 = x2 * x2; y4 = y2 * y2; f = wcs->x_coeff[0]*xmm + wcs->x_coeff[1]*ymm + wcs->x_coeff[2] + wcs->x_coeff[3]*x2 + wcs->x_coeff[4]*xy + wcs->x_coeff[5]*y2 + wcs->x_coeff[6]*x2y2 + wcs->x_coeff[7]*x3 + wcs->x_coeff[8]*x2y + wcs->x_coeff[9]*y2x + wcs->x_coeff[10]*y3 + wcs->x_coeff[11]*xmm*x2y2 + wcs->x_coeff[12]*xmm*cjunk; /* magnitude and color terms ignored + wcs->x_coeff[13]*mag + wcs->x_coeff[14]*mag*mag + wcs->x_coeff[15]*mag*mag*mag + wcs->x_coeff[16]*mag*xmm + wcs->x_coeff[17]*mag*(x2+y2) + wcs->x_coeff[18]*mag*xmm*(x2+y2) + wcs->x_coeff[19]*color; */ /* Derivative of X model wrt x */ fx = wcs->x_coeff[0] + wcs->x_coeff[3]*2.0*xmm + wcs->x_coeff[4]*ymm + wcs->x_coeff[6]*2.0*xmm + wcs->x_coeff[7]*3.0*x2 + wcs->x_coeff[8]*2.0*xy + wcs->x_coeff[9]*y2 + wcs->x_coeff[11]*(3.0*x2+y2) + wcs->x_coeff[12]*(5.0*x4 +6.0*x2*y2+y4); /* magnitude and color terms ignored wcs->x_coeff[16]*mag + wcs->x_coeff[17]*mag*2.0*xmm + wcs->x_coeff[18]*mag*(3.0*x2+y2); */ /* Derivative of X model wrt y */ fy = wcs->x_coeff[1] + wcs->x_coeff[4]*xmm + wcs->x_coeff[5]*2.0*ymm + wcs->x_coeff[6]*2.0*ymm + wcs->x_coeff[8]*x2 + wcs->x_coeff[9]*2.0*xy + wcs->x_coeff[10]*3.0*y2 + wcs->x_coeff[11]*2.0*xy + wcs->x_coeff[12]*4.0*xy*x2y2; /* magnitude and color terms ignored wcs->x_coeff[17]*mag*2.0*ymm + wcs->x_coeff[18]*mag*2.0*xy; */ /* Y plate model */ g = wcs->y_coeff[0]*ymm + wcs->y_coeff[1]*xmm + wcs->y_coeff[2] + wcs->y_coeff[3]*y2 + wcs->y_coeff[4]*xy + wcs->y_coeff[5]*x2 + wcs->y_coeff[6]*x2y2 + wcs->y_coeff[7]*y3 + wcs->y_coeff[8]*y2x + wcs->y_coeff[9]*x2y + wcs->y_coeff[10]*x3 + wcs->y_coeff[11]*ymm*x2y2 + wcs->y_coeff[12]*ymm*cjunk; /* magnitude and color terms ignored wcs->y_coeff[13]*mag + wcs->y_coeff[14]*mag*mag + wcs->y_coeff[15]*mag*mag*mag + wcs->y_coeff[16]*mag*ymm + wcs->y_coeff[17]*mag*x2y2 + wcs->y_coeff[18]*mag*ymm*x2y2 + wcs->y_coeff[19]*color; */ /* Derivative of Y model wrt x */ gx = wcs->y_coeff[1] + wcs->y_coeff[4]*ymm + wcs->y_coeff[5]*2.0*xmm + wcs->y_coeff[6]*2.0*xmm + wcs->y_coeff[8]*y2 + wcs->y_coeff[9]*2.0*xy + wcs->y_coeff[10]*3.0*x2 + wcs->y_coeff[11]*2.0*xy + wcs->y_coeff[12]*4.0*xy*x2y2; /* magnitude and color terms ignored wcs->y_coeff[17]*mag*2.0*xmm + wcs->y_coeff[18]*mag*ymm*2.0*xmm; */ /* Derivative of Y model wrt y */ gy = wcs->y_coeff[0] + wcs->y_coeff[3]*2.0*ymm + wcs->y_coeff[4]*xmm + wcs->y_coeff[6]*2.0*ymm + wcs->y_coeff[7]*3.0*y2 + wcs->y_coeff[8]*2.0*xy + wcs->y_coeff[9]*x2 + wcs->y_coeff[11]*(x2+3.0*y2) + wcs->y_coeff[12]*(5.0*y4 + 6.0*x2*y2 + x4); /* magnitude and color terms ignored wcs->y_coeff[16]*mag + wcs->y_coeff[17]*mag*2.0*ymm + wcs->y_coeff[18]*mag*(x2+3.0*y2); */ f = f - xi; g = g - eta; dx = ((-f * gy) + (g * fy)) / ((fx * gy) - (fy * gx)); dy = ((-g * fx) + (f * gx)) / ((fx * gy) - (fy * gx)); xmm = xmm + dx; ymm = ymm + dy; if ((fabs(dx) < tolerance) && (fabs(dy) < tolerance)) break; } /* Convert mm from plate center to plate pixels */ if (wcs->x_pixel_size == 0.0 || wcs->y_pixel_size == 0.0) return (1); x = (wcs->ppo_coeff[2] - xmm*1000.0) / wcs->x_pixel_size; y = (wcs->ppo_coeff[5] + ymm*1000.0) / wcs->y_pixel_size; /* Convert from plate pixels to image pixels */ *xpix = x - wcs->x_pixel_offset + 1.0 - 0.5; *ypix = y - wcs->y_pixel_offset + 1.0 - 0.5; /* If position is off of the image, return offscale code */ if (*xpix < 0.5 || *xpix > wcs->nxpix+0.5) return -1; if (*ypix < 0.5 || *ypix > wcs->nypix+0.5) return -1; return 0; } /* Mar 6 1995 Original version of this code * May 4 1995 Fix eta cross terms which were all in y * Jun 21 1995 Add inverse routine * Oct 17 1995 Fix inverse routine (degrees -> radians) * Nov 7 1995 Add half pixel to image coordinates to get astrometric * plate coordinates * Feb 26 1996 Fix plate to image pixel conversion error * * Mar 23 1998 Change names from plate*() to dss*() * Apr 7 1998 Change amd_i_coeff to i_coeff * Sep 4 1998 Fix possible divide by zero in dsspos() from Allen Harris, SAO * Sep 10 1998 Fix possible divide by zero in dsspix() from Allen Harris, SAO * * Oct 21 1999 Drop declaration of cond2r in dsspix() */