=pod

=head1 NAME



B<RegDiff:Differences Between Funtools and IRAF Regions>



=head1 SYNOPSIS




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



=head1 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:



=over 4






=item *

If a pixel is covered by two different regions expressions,
Funtools assigns the mask value of the B<first> region that
contains that pixel.  That is, successive regions B<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
B<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.




=item *

The B<PANDA> region has replaced the old PROS syntax in which
a B<PIE> accelerator was combined with an B<ANNULUS> accelerator
using B<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has been replaced by: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 B<AND> operator.




=item *

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.



=back





=head1 SEE ALSO



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



=cut
