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+<!-- =defdoc regdiff regdiff n -->
+<HTML>
+<HEAD>
+<TITLE>Differences Between Funtools and IRAF Regions</TITLE>
+</HEAD>
+<BODY>
+
+<!-- =section regdiff NAME -->
+<H2><A NAME="regdiff">RegDiff:Differences Between Funtools and IRAF Regions</A></H2>
+
+<!-- =section regdiff SYNOPSIS -->
+<H2>Summary</H2>
+Describes the differences between Funtools/ds9 regions and the old IRAF/PROS
+regions.
+
+<!-- =section regdiff DESCRIPTION -->
+<H2>Description</H2>
+<P>
+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:
+
+<UL>
+
+<P>
+<LI>If a pixel is covered by two different regions expressions,
+Funtools assigns the mask value of the <B>first</B> region that
+contains that pixel.  That is, successive regions <B>do not</b>
+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</B> 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.
+
+<P>
+<LI> The <B>PANDA</B> region has replaced the old PROS syntax in which
+a <B>PIE</B> accelerator was combined with an <B>ANNULUS</B> accelerator
+using <B>AND</B>. That is,
+<PRE>
+  ANNULUS(20,20,0,15,n=4) & PIE(20,20,0,360,n=3)
+</PRE>
+has been replaced by:
+<PRE>
+  PANDA(20,20,0,360,3,0,15,4)
+</PRE>
+The PROS syntax was inconsistent with the meaning of the <B>AND</B> operator.
+
+<P>
+<LI> 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
+<A HREF="./regions.html">Spatial Region Filtering</A>
+for more information.
+
+</UL>
+
+<!-- =section regdiff SEE ALSO -->
+<!-- =text See funtools(n) for a list of Funtools help pages -->
+<!-- =stop -->
+
+<P>
+<A HREF="./help.html">Go to Funtools Help Index</A>
+
+<H5>Last updated: November 16, 2005</H5>
+
+</BODY>
+</HTML>