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Diffstat (limited to 'ast/erfa/gc2gde.c')
| -rw-r--r-- | ast/erfa/gc2gde.c | 208 |
1 files changed, 208 insertions, 0 deletions
diff --git a/ast/erfa/gc2gde.c b/ast/erfa/gc2gde.c new file mode 100644 index 0000000..43ed61d --- /dev/null +++ b/ast/erfa/gc2gde.c @@ -0,0 +1,208 @@ +#include "erfa.h" + +int eraGc2gde ( double a, double f, double xyz[3], + double *elong, double *phi, double *height ) +/* +** - - - - - - - - - - +** e r a G c 2 g d e +** - - - - - - - - - - +** +** Transform geocentric coordinates to geodetic for a reference +** ellipsoid of specified form. +** +** Given: +** a double equatorial radius (Notes 2,4) +** f double flattening (Note 3) +** xyz double[3] geocentric vector (Note 4) +** +** Returned: +** elong double longitude (radians, east +ve) +** phi double latitude (geodetic, radians) +** height double height above ellipsoid (geodetic, Note 4) +** +** Returned (function value): +** int status: 0 = OK +** -1 = illegal f +** -2 = illegal a +** +** Notes: +** +** 1) This function is based on the GCONV2H Fortran subroutine by +** Toshio Fukushima (see reference). +** +** 2) The equatorial radius, a, can be in any units, but meters is +** the conventional choice. +** +** 3) The flattening, f, is (for the Earth) a value around 0.00335, +** i.e. around 1/298. +** +** 4) The equatorial radius, a, and the geocentric vector, xyz, +** must be given in the same units, and determine the units of +** the returned height, height. +** +** 5) If an error occurs (status < 0), elong, phi and height are +** unchanged. +** +** 6) The inverse transformation is performed in the function +** eraGd2gce. +** +** 7) The transformation for a standard ellipsoid (such as ERFA_WGS84) can +** more conveniently be performed by calling eraGc2gd, which uses a +** numerical code to identify the required A and F values. +** +** Reference: +** +** Fukushima, T., "Transformation from Cartesian to geodetic +** coordinates accelerated by Halley's method", J.Geodesy (2006) +** 79: 689-693 +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double aeps2, e2, e4t, ec2, ec, b, x, y, z, p2, absz, p, s0, pn, zc, + c0, c02, c03, s02, s03, a02, a0, a03, d0, f0, b0, s1, + cc, s12, cc2; + + +/* ------------- */ +/* Preliminaries */ +/* ------------- */ + +/* Validate ellipsoid parameters. */ + if ( f < 0.0 || f >= 1.0 ) return -1; + if ( a <= 0.0 ) return -2; + +/* Functions of ellipsoid parameters (with further validation of f). */ + aeps2 = a*a * 1e-32; + e2 = (2.0 - f) * f; + e4t = e2*e2 * 1.5; + ec2 = 1.0 - e2; + if ( ec2 <= 0.0 ) return -1; + ec = sqrt(ec2); + b = a * ec; + +/* Cartesian components. */ + x = xyz[0]; + y = xyz[1]; + z = xyz[2]; + +/* Distance from polar axis squared. */ + p2 = x*x + y*y; + +/* Longitude. */ + *elong = p2 > 0.0 ? atan2(y, x) : 0.0; + +/* Unsigned z-coordinate. */ + absz = fabs(z); + +/* Proceed unless polar case. */ + if ( p2 > aeps2 ) { + + /* Distance from polar axis. */ + p = sqrt(p2); + + /* Normalization. */ + s0 = absz / a; + pn = p / a; + zc = ec * s0; + + /* Prepare Newton correction factors. */ + c0 = ec * pn; + c02 = c0 * c0; + c03 = c02 * c0; + s02 = s0 * s0; + s03 = s02 * s0; + a02 = c02 + s02; + a0 = sqrt(a02); + a03 = a02 * a0; + d0 = zc*a03 + e2*s03; + f0 = pn*a03 - e2*c03; + + /* Prepare Halley correction factor. */ + b0 = e4t * s02 * c02 * pn * (a0 - ec); + s1 = d0*f0 - b0*s0; + cc = ec * (f0*f0 - b0*c0); + + /* Evaluate latitude and height. */ + *phi = atan(s1/cc); + s12 = s1 * s1; + cc2 = cc * cc; + *height = (p*cc + absz*s1 - a * sqrt(ec2*s12 + cc2)) / + sqrt(s12 + cc2); + } else { + + /* Exception: pole. */ + *phi = ERFA_DPI / 2.0; + *height = absz - b; + } + +/* Restore sign of latitude. */ + if ( z < 0 ) *phi = -*phi; + +/* OK status. */ + return 0; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** All rights reserved. +** +** This library is derived, with permission, from the International +** Astronomical Union's "Standards of Fundamental Astronomy" library, +** available from http://www.iausofa.org. +** +** The ERFA version is intended to retain identical functionality to +** the SOFA library, but made distinct through different function and +** file names, as set out in the SOFA license conditions. The SOFA +** original has a role as a reference standard for the IAU and IERS, +** and consequently redistribution is permitted only in its unaltered +** state. The ERFA version is not subject to this restriction and +** therefore can be included in distributions which do not support the +** concept of "read only" software. +** +** Although the intent is to replicate the SOFA API (other than +** replacement of prefix names) and results (with the exception of +** bugs; any that are discovered will be fixed), SOFA is not +** responsible for any errors found in this version of the library. +** +** If you wish to acknowledge the SOFA heritage, please acknowledge +** that you are using a library derived from SOFA, rather than SOFA +** itself. +** +** +** TERMS AND CONDITIONS +** +** Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions +** are met: +** +** 1 Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** +** 2 Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** +** 3 Neither the name of the Standards Of Fundamental Astronomy Board, +** the International Astronomical Union nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS +** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE +** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, +** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, +** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN +** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +** POSSIBILITY OF SUCH DAMAGE. +** +*/ |