ftp://fits.cv.nrao.edu/fits/src/wcs/worldpos.tar.gz
16489 Oct 13 17:04 worldpos.tar.gz
This is the code which was mentioned during the FITS-WCS BOF at ADASS'94.
The tar file contains:
tar tvf worldpos.tar
rwxr-xr-x106/16 0 Oct 13 17:04 1994 worldpos/
rw-r--r--106/16 17535 Oct 13 16:01 1994 worldpos/worldpos.c
rw-r--r--106/16 5143 Oct 13 16:23 1994 worldpos/testpos.c
rw-r--r--106/16 2721 Oct 13 17:04 1994 worldpos/testpos.ref
rw-r--r--106/16 25265 Oct 10 16:46 1994 worldpos/COPYING.LIB-2.0
rw-r--r--106/16 2277 Oct 13 16:31 1994 worldpos/Makefile
I append selected text from file worldpos.c.
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/* worldpos.c -- WCS Algorithms from Classic AIPS.
Copyright (C) 1994
Associated Universities, Inc. Washington DC, USA.
This library is free software; you can redistribute it and/or modify it
under the terms of the GNU Library General Public License..
These two ANSI C functions, worldpos() and xypix(), perform
forward and reverse WCS computations for 8 types of projective
geometries ("-SIN", "-TAN", "-ARC", "-NCP", "-GLS", "-MER", "-AIT"
and "-STG"):
worldpos() converts from pixel location to RA,Dec
xypix() converts from RA,Dec to pixel location
where "(RA,Dec)" are more generically (long,lat). These functions
are based on the WCS implementation of Classic AIPS, an
implementation which has been in production use for more than ten
years. See the two memos by Eric Greisen
ftp://fits.cv.nrao.edu/fits/documents/wcs/aips27.ps.Z
ftp://fits.cv.nrao.edu/fits/documents/wcs/aips46.ps.Z
for descriptions of the 8 projective geometries and the
algorithms. Footnotes in these two documents describe the
differences between these algorithms and the 1993-94 WCS draft
proposal (see URL below). In particular, these algorithms support
ordinary field rotation, but not skew geometries (CD or PC matrix
cases). Also, the MER and AIT algorithms work correctly only for
CRVALi=(0,0). Users should note that GLS projections with yref!=0
will behave differently in this code than in the draft WCS
proposal. The NCP projection is now obsolete (it is a special
case of SIN). WCS syntax and semantics for various advanced
features is discussed in the draft WCS proposal by Greisen and
Calabretta at:
ftp://fits.cv.nrao.edu/fits/documents/wcs/wcs.all.ps.Z
...
int worldpos(double xpix, double ypix, double xref, double yref,
double xrefpix, double yrefpix, double xinc, double yinc, double rot,
char *type, double *xpos, double *ypos)
...
int xypix(double xpos, double ypos, double xref, double yref,
double xrefpix, double yrefpix, double xinc, double yinc, double rot,
char *type, double *xpix, double *ypix)
...
Donald C. Wells Associate Scientist dwells@nrao.edu
http://fits.cv.nrao.edu/~dwells
National Radio Astronomy Observatory +1-804-296-0277
520 Edgemont Road, Charlottesville, Virginia 22903-2475 USA