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+=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+has been replaced by: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