[gdal-dev] OGR and GEOS

[Kevin Webb]

At 11:07 AM 12/22/2008, Frank Warmerdam wrote:
>Kevin Webb wrote:
>>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?
>
>Kevin,
>
>The Intersects() is bounding box based without GEOS, and based on
>actual geometry intersection if it is available.  That is presumably
>why your results differ.
>
>For a large number of people OGR is just fine without GEOS, so I see
>no reason to make it a fixed dependency.  It might be prudent to better
>document the caveats of operating without it.
>
>Best regards,
>--
>---------------------------------------+--------------------------------------
>I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
>light and sound - activate the windows | http://pobox.com/~warmerdam
>and watch the world go round - Rush    | Geospatial Programmer for Rent


Thank you for your reply Frank.

Giving the documentation a boost should provide some relief.




KFW



-----------------------------------------
Kevin Webb
Programmer/Analyst
Cornell Lab of Ornithology
159 Sapsucker Woods Rd.
Ithaca, NY 14850
Tel: 607.254.2103
Fax: 607.254.2415
kfw4 at cornell.edu
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