[gdal-dev] OGR and GEOS

[Ragi Y. Burhum]

>
> Date: Mon, 22 Dec 2008 09:37:15 -0500
> From: Kevin Webb <kfw4 at cornell.edu>
> Subject: [gdal-dev] OGR and GEOS
> To: gdal-dev at lists.osgeo.org
> Message-ID:
>        <6.2.1.2.2.20081222085228.03fe8f40 at 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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