[postgis-devel] [PostGIS] #240: ST_SimplifyPreserveTopology documentation unclear on intersections within a MultiPolygon

[PostGIS]

#240: ST_SimplifyPreserveTopology documentation unclear on intersections within a
MultiPolygon
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  Reporter:  perchrh  |       Owner:  robe         
      Type:  defect   |      Status:  new          
  Priority:  medium   |   Milestone:  PostGIS 1.5.0
 Component:  postgis  |     Version:               
Resolution:           |    Keywords:               
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Comment (by perchrh):

 In the ESRI shapefile standard, a Record with shapetype Polygon is a
 collection of zero or more Rings (in other terms: a MultiPolygon
 containing multiple Polygons). The rings may intersect each other and
 cannot self-intersect.

 It is clear that ST_SimplifyPreserveTopology doesn't introduce self-
 intersections and doesn't introduce intersections between Polygons if
 there were none in the input.

 My question, that I didn't manage to get answered by a quick look at the
 code is, is the processing of these valid MultiPolygons with intersecting
 Polygons guaranteed to result in a MultiPolygon with no new intersections?
 Or does it just guarantee that the intersection count will not be higher
 than in the input? To put it another way, if I have a MultiPolygon with
 three polygons, two of them intersecting each other (A and B), is it
 possible that B and C will intersect after ST_SimplifyPreserveTopology?

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/240#comment:7>
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