At 12:46 PM 12/22/2008, Ragi Y. Burhum wrote:
Date: Mon, 22 Dec 2008 09:37:15 -0500
From: Kevin Webb <<mailto:k...@cornell.edu>k...@cornell.edu>
Subject: [gdal-dev] OGR and GEOS
To: <mailto:gdal-dev@lists.osgeo.org>gdal-dev@lists.osgeo.org
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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
Thank you for your reply Ragi.
You are correct, I should not have used to word "deterministic;" with-GEOS
or without-GEOS I produced the same output
result for each processing run.
As Frank suggested in his post, I think more clarity is needed in the
write-ups for the methods that use alternate
processing logic with-GEOS installed when compared to a similar operation
without-GEOS installed.
KFW
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Kevin Webb
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Cornell Lab of Ornithology
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Ithaca, NY 14850
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Fax: 607.254.2415
k...@cornell.edu
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