[postgis-devel] [PostGIS] #1198: st_union fails on some sets of polygons. snapping

[PostGIS]

#1198: st_union fails on some sets of polygons. snapping
-----------------------------------------------------------+----------------
 Reporter:  dmiranda                                       |       Owner:  pramsey      
     Type:  defect                                         |      Status:  new          
 Priority:  medium                                         |   Milestone:  PostGIS 2.0.0
Component:  postgis                                        |     Version:  trunk        
 Keywords:  st_union topologyexception noded intersection  |  
-----------------------------------------------------------+----------------
 How to reproduce:
   -load either the attached shapefile or the sql into postgis
   -run the query:
    select st_union(geom) from st_union_topology_exception;
   -The following message should appear:
 ERROR: GEOSUnionCascaded: TopologyException: found non-noded intersection
 between LINESTRING (-54.7158 -28.0099, -54.7156 -28.0116) and LINESTRING
 (-54.7158 -28.0099, -54.7158 -28.0119) at -54.7158 -28.0099
 SQL state: XX000

 Other observations:
 -st_isvalid returns true for all the polygons
 -snapping may get rid of the problem (select
 st_union(st_snaptogrid(geom,0.00000000001)) from
 st_union_topology_exception; finishes without errors)
 -buffering by zero does not get rid of the problem
 -snapping stops solving the problem at 0.00000000000001, presumably near
 the float 64 resolution.

 possibly related to #575, #1045 and/or #1173 (error message is similar)

 Version:
 Ubuntu 11.04
 Postgresql 9.1
 postgis 2.0.0svn Rev: 7856 Last Changed Date: 2011-09-15 14:43:57
 GEOS 3.4.0dev Rev: 3465 Last Changed Date: 2011-09-12 01:47:39

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/1198>
PostGIS <http://trac.osgeo.org/postgis/>
The PostGIS Trac is used for bug, enhancement & task tracking, a user and developer wiki, and a view into the subversion code repository of PostGIS project.