image orientation on the screen

[Barry M. Schlesinger]

In article <5bgjmp$3fe at noao.edu>, seaman at noao.edu (Rob Seaman) writes...
>Mike Newberry <mnewberry at axres.com> writes:
> 
>> ... I wonder if
>> there is a commonly adopted "standard":
>> 
>> Where should pixel (0,0) of a FITS file be displayed on the screen-- in
>> the upper left or lower left corner?
> 
>Well, IRAF/Ximtool/SAOimage (and others) put the origin at the lower left.
>A FITS file is usually considered to be in fortran storage order, so the
>lines fill left to right before they fill bottom to top....
> 
>The computer graphics "standard" is to have the origin at the upper left.
>Many systems both in and out of astronomy allow the origin to be placed
>in any corner (either overtly, or via syntax that flips axes)....
> 
>> And for which ever is correct, should the screen image match the
>> orientation (i.e., no mirror reversal) of what the CCD saw?
> 
>... It isn't entirely clear how to interpret the orientation of what a
>detector array (not limited to CCDs, or physical detectors in general
>for that matter) "sees".  An orientation may only be defined at the
>point that the image is actually displayed to the user.
> 
>         [detailed discussion omitted]
> 
>Note that FITS WCS provides a (potentially) more rigorous mechanism to
>address these issues.  (FITS might also conceivably benefit from the
>experiences of the remote sensing/GIS communities.)
> 

The current draft of the World Coordinate Systems (WCS) proposal has 
some discussion on these points and can be found via
http://fits.cv.nrao.edu/documents/wcs/wcs/html

				Barry Schlesinger
				FITS Support Office
				GSFC/ADF