iraf.net

IRAF provides two world coordinate systems (WCS) which include arbitrary polynomial distortions. These are not FITS standard, particular as they predate the most recent FITS standards and the current standards do not provide such general distortion methods.These WCS are used with NOAO data, most notably with the Mosaic and NEWFIRM imagers. For Mosaic the raw data is produced with TNX and the pipeline WCS calibrations use ZPX. ZPX is now preferred because some of the distortions are removed by taking into account the main effect of a pin-cushion effect in the corrector. This allows fitting of the remaining distortions with a lower order 2D polynomial.The purpose of this posting is to point to references that provide a description for people to write their own code for evaluation the WCS given than not all software supports these. The ZPX description is new as of this posting.The references are:http://iraf.noao.edu/projects/ccdmosaic/zpx.html
http://iraf.noao.edu/projects/ccdmosaic/tnx.htmlFrank Valdes