[postgis-devel] [PostGIS] #922: Have ST_Union aggregate use UnaryUnion from GEOS-3.0.0

PostGIS trac at osgeo.org
Sat Apr 23 03:22:19 PDT 2011

#922: Have ST_Union aggregate use UnaryUnion from GEOS-3.0.0
 Reporter:  strk         |       Owner:  pramsey      
     Type:  enhancement  |      Status:  new          
 Priority:  medium       |   Milestone:  PostGIS 2.0.0
Component:  postgis      |     Version:  trunk        
 Keywords:               |  
 Current code of PostGIS uses GEOSUnionCascaded only for polygons, and
 that's even correct because the GEOS C-API GEOSUnionCascade would throw an
 exception if anything but (multi)Polygons are given.

 Instead the new GEOSUnaryUnion interface from GEOS-3.0.0 accepts any kind
 of geometry. Internally uses Cascaded union for polygons but also does
 special handling of points and lines. See
 http://trac.osgeo.org/geos/ticket/392 for an example case in which the
 UnaryUnion works whereas normal union doesn't.

 Always using UnaryUnion when build against GEOS-3.3.0 would then simplify
 the code and improve union robustness.

Ticket URL: <http://trac.osgeo.org/postgis/ticket/922>
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