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Institut für Astronomie und Astrophysik

Abteilung Astronomie

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Table of Contents



Introduction

This directory contain IDL procedures for manipulating FITS or STSDAS images which include header keywords specifying the coordinate system. The FITS or STSDAS header must follow the specification in the FITS draft proposal "Representations of Celestial Coordinates in FITS" by Eric Greisen and Mark Calabretta. Documentation for this proposal can be obtained from http://fits.cv.nrao.edu/documents/wcs/wcs.html. (Note that -- as of November 1998 -- the preferred notation for the coordinate description (CD) matrix in a FITS header is with and underscore, i.e., CDn_m.)

Users should be aware that FITS defines the center of the first pixel in the array to have coordinates (1,1). This differs from the IDL convention where the first pixel has coordinates (0,0). Whenever an (X,Y) position is extracted or inserted into a FITS/STSDAS header then this difference must be accounted for.

Special astrometry procedures are required for the ST Guidestar Survey Images which were released on CD-Rom in early 1994. Information about the Guidestar images can be obtained from http://www-gsss.stsci.edu/img_cdrom/img_top.html and the Guidestar images can also be obtained from the SKYVIEW facility. The Schmidt plates used in this survey have a highly nonlinear plate solution that is not covered by the Greisen & Calabretta conventions. The procedures GSSSEXTAST, GSSSXYAD, and GSSSADXY are the Guidestar survey analogues of the procedures EXTAST, XY2AD, and ADXY for standard astrometry. All the astrometry procedures in the library will test for a Guidestar image header (by looking for the 'PPO1' keyword) and call the appropriate procedures. The procedure GSSS_STDAST will convert the astrometry in a guidestar image header to an standard tangent projection with very slightly degraded accuracy.

The procedures in this directory will call the procedures wcssph2xy and wcsxy2sph in the astro directory A couple of procedures in other directories also use the FITS world coordinate system including IMCONTOUR and IMDBASE.


Index of Subroutines

ABSCAL Apply the FITS BZERO and BSCALE keyword values to a data array
AD2XY Compute X and Y from native coordinates and a FITS astrometry structure
ADXY Use a FITS header to convert astronomical to pixel coordinates
CONS_DEC Obtain the X and Y coordinates of a line of constant declination
CONS_RA Obtain the X and Y coordinates of a line of constant right ascension
EXTAST Extract ASTrometry parameters from a FITS image header.
FITS_CD_FIX Update obsolete representations of the CD matrix in a FITS header
GET_EQUINOX Return the equinox value from a FITS header.
GETROT Return the rotation and plate scale of an image from its FITS header
GSSS_STDAST Insert the closest tangent projection astrometry into an GSSS Image
GSSSADXY Converts RA and DEC (J2000) to (X,Y) for an STScI GuideStar image.
GSSSEXTAST Extract IDL astrometry structure from a ST Guide Star Survey FITS header
GSSSXYAD Convert (X,Y) coordinates in a STScI Guide Star image to RA and Dec
HASTROM Linear transformation of an image to align it with a reference image
HBOXAVE Box average an image array and update the FITS header array
HCONGRID CONGRID an image and update astrometry in a FITS header
HEULER Change the coordinate system of a FITS header or astrometry structure
HEXTRACT Extract a subimage from an array and update astrometry in FITS header
HPRECESS Precess the astrometry in a FITS header to a new equinox
HREBIN Expand or contract a FITS image using (F)REBIN and update the header
HREVERSE Reverse an image about either dimension and update FITS astrometry
HROT Rotate an image and create new FITS header with updated astrometry.
HROTATE Apply the IDL ROTATE function and update astrometry in a FITS header
MAKE_ASTR Build an astrometry structure from input parameter values
PUTAST Put WCS astrometry parameters into a given FITS header.
STARAST Compute astrometric solution using positions of 2 or 3 reference stars
WCS_DEMO Demonstrate the basic capabilities of procedures WCSSPH2XY & WCSXY2SPH
WCS_GETPOLE Compute the coordinates of the native pole for a non-polar projection
WCS_ROTATE Rotate between standard (e.g. celestial) and native coordinates
WCSSPH2XY Convert spherical coordinates to x and y (map) angular coordinates
WCSXY2SPH Convert x and y (map) coordinates to spherical coordinates
WFPC2_METRIC Compute the distortion in a WFPC2 image and optionally return coordinates
XY2AD Compute R.A. and Dec from X and Y and a FITS astrometry structure
XYXY To use a pair of headers to convert X/Y positions from one frame to another.
Last modified by pro2html on 2008 November 09 at 04:11 UTC

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Jörn Wilms (wilms@astro.uni-tuebingen.de)
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