[postgis-devel] [PostGIS] #1706: TopoGeo_AddPolygon not adding polygons

[PostGIS]

#1706: TopoGeo_AddPolygon not adding polygons
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 Reporter:  pramsey   |       Owner:  strk         
     Type:  defect    |      Status:  new          
 Priority:  medium    |   Milestone:  PostGIS 2.0.0
Component:  topology  |     Version:  trunk        
 Keywords:            |  
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Comment(by strk):

 Alright, the self-noded boundary of the second polygon being added is
 fine.

 Then we find existing edges that intersect the new line and we find the
 first polygon boundary
 edge.

 When we go on to compute the difference between the self-noded boundary
 and the existing edge.

 At that point we snap the new edge to the existing one and here the error
 is introduced.

 Look at the pictures. The first one shows the old edge (green) and the new
 edge (red) before snapping. The second shows the same thing _after_
 snapping the new edge to the old edge.
 You can see the snapping is drastically wrong. I mean... if it snapped to
 _closest_ point rather than to first point under threshold it would have
 done a much better work.

 That also explains why a lower tolerance works better (snaps better).
 I really think we should fix ST_Snap to snap to the closest vertex for
 this to work better.

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/1706#comment:4>
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