% @(#)WCS.alq	17.1.1.1 (ESO-IPG) 01/25/02 17:43:14 


			World Coordinate System
			-----------------------

We're beginning to integrate a true (non-linear) World Coordinate System
into MIDAS.

This implementation is based on the subroutine library WCSLIB (written in C)
of Mark Calabretta (mcalabre@atnf.csiro.au) as used in the AIPS project.
For details about the concepts regarding a WCS for astronomical images see 
the the paper by Eric Greisen and Mark Calabretta, "Representation of Celestial 
Coordinates in FITS". 

Until now all MIDAS applications supported only a linear WCS, therefore, we put 
in a safety mechanism to avoid any unforeseen problems with existing procedures
and applications:
Keyword AUX_MODE(10) serves as a switch to en/disable the usage of a "true"
WCS in the transformation of frame pixels to world coordinates (and vice 
versa). By default AUX_MODE(10) is set to 0 which leads to the continuing
usage of just a linear WCS, thus disabling the new WCS implementation.
Setting AUX_MODE(10) to 99 enables new WCS.

Currently the only MIDAS command concerned and visible to the user is the
GET/CURSOR command.
If an image which contains the necessary FITS keywords for WCS translation is 
loaded, this information is used to display the world coordinates of the pixel 
specified by the cursor.

The application procedure `getcoord.prg' converts frame pixels to world
coordinates according to the specified projection in the WCS related FITS
keywords independent of the setting of AUX_MODE(10).