[gdal-dev] Topological Union?

Craig Miller craig.miller at spatialminds.com
Sat Sep 13 03:21:43 EDT 2008

I wound up using Spatialite (SQLite + WKB/GEOS support) instead of writing my own code.  It was very fast and easy to setup.  It would make a perfect teaching/learning tool for anyone who wants to learn about SQL and spatial operators.


-----Original Message-----
From: Mateusz Loskot [mailto:mateusz at loskot.net] 
Sent: Friday, August 29, 2008 10:22 AM
To: Craig Miller; Craig Miller
Cc: 'Brent Fraser'; gdal-dev at lists.osgeo.org; 'Brent Fraser'; gdal-dev at lists.osgeo.org
Subject: Re: [gdal-dev] Topological Union?

Craig Miller wrote:
> Thanks Brent.  I'm looking for a C/C++ solution.  I'll take a look at 
> the other polygon processing libraries as well as the level of effort 
> in porting JTS Cascaded Unions to Geos... that's a conversation for a 
> different mailing list though.


I agree with Brent that performance is/may not be very impressive.
In OGR, this is mostly caused by a need to convert OGRGeometry type to GEOS geometry type [1] - allocating & copying coordinates data is expansive.

However, if you are developing your own solution in C++, you can avoid this by defining your geometry in terms of interface of geos::geom::Geometry or - following design pattern called adapter, you can provide a thin wrapper on your geometry type that will make it accessible to GEOS engine. This way you should get rid of major bottleneck of OGR<->GEOS interoperability.

[1] http://trac.osgeo.org/gdal/browser/trunk/gdal/ogr/ogrgeometry.cpp#L2105

Best regards,
Mateusz Loskot, http://mateusz.loskot.net Charter Member of OSGeo, http://osgeo.org

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