## RegDiff:Differences Between Funtools and IRAF Regions

## Summary

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  has been replaced by: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.

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##### Last updated: November 16, 2005