Hello Todd: Thanks for the information re: the disparity between the geometry constructions and tests in ogr (geos). In terms of visible-extents clipping (draw / do-not-draw decisions), I suppose a small expansion of the clipping rectangle will bridge the gap in precision. For more stringent topology requirements (
e.g., strict point-in-polygon tests that guarantee mutual exclusivity between adjacent polygons) the disparity should not be ignored.<br><br>Frank & Mateusz: Thanks for looking into the ogr performance issue.<br>
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Jack<br><br><br><div><span class="gmail_quote">On 3/23/07, <b class="gmail_sendername">Mateusz Loskot</b> <<a href="mailto:mateusz@loskot.net">mateusz@loskot.net</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Frank Warmerdam wrote:<br>> Jack Riley wrote:<br>>> It appears that the FWTools v1.0.9-and-earlier TopologyException is<br>>> limited to situations where one of the two polynomials being tested<br>>> for Intersection() is completely within the other. In other words,
<br>>> the Intersection() test in "old" versions of FWTools/GDAL works--and<br>>> works "fast"--if the two polynomials actually intersect. So, my<br>>> workaround is to use FWTools v1.0.9
(or earlier) and condition any<br>>> call to Intersection() with Disjoint() or Contains() test(s). The<br>>> question remaining is: can FWTools v1.1.0+/GDAL revert back to the<br>>> use of the "old" and "fast" Intersection() code, adding in a test of
<br>>> Disjoint()/Contains() to circumvent the TopologyException?<br>><br>> Jack,<br>><br>> I've asked Mateusz who is a GEOS guru too to look into this issue.<br><br>Jack,<br><br>I'm going to try to reproduce your results and tests today and tomorrow.
<br>I will report about results.<br><br>Cheers<br>--<br>Mateusz Loskot<br><a href="http://mateusz.loskot.net">http://mateusz.loskot.net</a><br></blockquote></div><br>