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Describes the differences between Funtools/ds9 regions and the old IRAF/PROS
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has been replaced by:
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.
Go to Funtools Help Index
Last updated: November 16, 2005