RegDiff - Differences Between Funtools and IRAF Regions
Describes the differences between Funtools/ds9 regions and the old
IRAF/PROS regions.
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has been replaced by: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 funtools(7) for a list of Funtools help pages