> > Date: Mon, 22 Dec 2008 09:37:15 -0500 > From: Kevin Webb <k...@cornell.edu> > Subject: [gdal-dev] OGR and GEOS > To: gdal-dev@lists.osgeo.org > Message-ID: > <6.2.1.2.2.20081222085228.03fe8...@postoffice7.mail.cornell.edu> > Content-Type: text/plain; charset="us-ascii"; format=flowed > > Greetings! > > The documentation for the OGRGeometry class mentions the GEOS library in a > few of the > method definitions, but I wonder if there is a "stronger" OGR dependency on > the GEOS > library than the documentation suggests. Perhaps GEOS should be a required > library. > > I had done some processing using OGRGeometry::Intersects() without the GEOS > library > installed, I then installed GEOS to run the same tests using > OGRGeometry::Distance(). > After installing GEOS, but before running the OGRGeometry::Distance() > tests, I re-ran the > code using OGRGeometry::Intersects() and noticed different intersection > results. > > Before-GEOS, the Intersects() method indicated intersection with 2 layer > polygons. After-GEOS, > the Intersects() method indicated intersection with 1 layer polygon. Note: > After-GEOS results > for both Intersects() and Distance() == 0 were the same. > > Should the GEOS library be a requirement for deterministic OGR processing? > > > Thank you. > > > KFW > > With GEOS and without GEOS you will get "deterministic" results. The difference is that the algorithm to calculate intersections without GEOS is simpler - just bounding box intersections. You want GEOS installed.
- Ragi
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