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<P>I found what I think to be a bug in the Intersection routine. </P>
<P>I defined a polygon with the following wkt: POLYGON( (0 0, 1 0, 1 1, 0 1, 0
0), (.5 .1, 1 .5, .5 .9, .5 .1)) This polygon has an exterior ring that is
a square, and one interior ring that is a triangle. The interior ring
touches the exterior ring in one point. I believe this is considered a
valid polygon.</P>
<P>When I call the <FONT size=2>GEOSIntersection method using this polygon for
both parameters, I would expect to get back the same polygon. Instead I
get back a geometry collection of 8 linestrings and a polygon:</FONT></P><FONT
size=2>
<P>GEOMETRYCOLLECTION (LINESTRING (0.0000000000000000 0.0000000000000000,
1.0000000000000000 0.0000000000000000), LINESTRING (1.0000000000000000
0.0000000000000000, 1.0000000000000000 0.5000000000000000), LINESTRING
(1.0000000000000000 0.5000000000000000, 1.0000000000000000 1.0000000000000000),
LINESTRING (1.0000000000000000 1.0000000000000000, 0.0000000000000000
1.0000000000000000), LINESTRING (0.0000000000000000 1.0000000000000000,
0.0000000000000000 0.0000000000000000), LINESTRING (0.5000000000000000
0.1000000000000000, 1.0000000000000000 0.5000000000000000), LINESTRING
(1.0000000000000000 0.5000000000000000, 0.5000000000000000 0.9000000000000000),
LINESTRING (0.5000000000000000 0.9000000000000000, 0.5000000000000000
0.1000000000000000), POLYGON ((1.0000000000000000 0.0000000000000000,
0.0000000000000000 0.0000000000000000, 0.0000000000000000 1.0000000000000000,
1.0000000000000000 1.0000000000000000, 1.0000000000000000 0.5000000000000000,
1.0000000000000000 0.0000000000000000), (1.0000000000000000 0.5000000000000000,
0.5000000000000000 0.9000000000000000, 0.5000000000000000 0.1000000000000000,
1.0000000000000000 0.5000000000000000)))</P></FONT>
<P><FONT size=2>The last polygon appears to be equivalent to my input, but with
one extra point in the exterior ring. The 8 linestrings appear to be the
pieces of the </FONT><FONT size=2>boundary of the polygon.</FONT></P>
<P><FONT size=2>I believe this is a bug. If I change the input polygon so that
the interior ring doesn't touch the exterior ring, I get the expected
result.</FONT></P>
<P><FONT size=2>Thanks,</FONT></P>
<P><FONT size=2>Pete
Gerritson</P></FONT></FONT></FONT></DIV></FONT></DIV></BODY></HTML>