NAME

       RegDiff - Differences Between Funtools and IRAF Regions

SYNOPSIS

       Describes the differences between Funtools/ds9 regions and the old IRAF/PROS regions.

DESCRIPTION

       We have tried to make Funtools regions compatible with their predecessor, IRAF/PROS
       regions. For simple regions and simple boolean algebra between regions, there should be no
       difference between the two implementations.  The following is a list of differences and
       incompatibilities between the two:

       •   If a pixel is covered by two different regions expressions, Funtools assigns the mask
           value of the first region that contains that pixel.  That is, successive regions do
           not overwrite previous regions in the mask, as was the case with the original PROS
           regions.  This means that one must define overlapping regions in the reverse order in
           which they were defined in PROS.  If region N is fully contained within region M, then
           N should be defined before M, or else it will be "covered up" by the latter. This
           change is necessitated by the use of optimized filter compilation, i.e., Funtools only
           tests individual regions until a proper match is made.

       •   The PANDA region has replaced the old PROS syntax in which a PIE accelerator was
           combined with an ANNULUS accelerator using AND. That is,

             ANNULUS(20,20,0,15,n=4) & PIE(20,20,0,360,n=3)

           has been replaced by:

             PANDA(20,20,0,360,3,0,15,4)

           The PROS syntax was inconsistent with the meaning of the AND operator.

       •   The meaning of pure numbers (i.e., without format specifiers) in regions has been
           clarified, as has the syntax for specifying coordinate systems. See the general
           discussion on Spatial Region Filtering for more information.

SEE ALSO

       See funtools(7) for a list of Funtools help pages