[Qgis-developer] new geom function: combine cascaded

Carson Farmer carson.farmer at gmail.com
Sun Apr 11 18:07:00 EDT 2010


Hello devs,

I have recently added a new function to QgsGeometry which speeds
things up when combining (unioning) multiple geometries. It uses the
cascaded union function recently added to GEOS [1,2], and can provide
over 10 times speed-ups in many cases (my own tests [3] have shown a
14 times speed-up with even a relatively small polygon layer). Since
I'm not really a C++ developer, I haven't committed these changes yet.
Attached is a diff with the necessary changes. If some of you would
like to test and take a look at my code, it would be much appreciated.
As of now things compile and run nicely, but it's possible I've missed
something important.

Cheers,

Carson

[1] http://lin-ear-th-inking.blogspot.com/search?q=cascaded
[2] http://blog.cleverelephant.ca/2009/01/must-faster-unions-in-postgis-14.html
[3] http://www.carsonfarmer.com/?p=587

-- 
Carson J. Q. Farmer
ISSP Doctoral Fellow
National Centre for Geocomputation
National University of Ireland, Maynooth,
http://www.carsonfarmer.com/
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