[postgis-devel] [PostGIS] #1188: Implement topology.ST_RemEdgeNewFace

[PostGIS]

#1188: Implement topology.ST_RemEdgeNewFace
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 Reporter:  strk      |       Owner:  strk@…         
     Type:  task      |      Status:  new            
 Priority:  medium    |   Milestone:  PostGIS 2.0.0  
Component:  topology  |     Version:  trunk          
 Keywords:            |  
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Comment(by chodgson):

 In what situations would removing an edge NOT result in merging two faces
 into a new face? I can only think of two:

 1) one of the faces of the original line is the outermost face, boundary
 face, universal face, whatever you call it... not sure if you actually
 create a NEW such face or simply merge the existing ones onto it? However
 I imagine you could return the id of this face, new or not.

 2) the edge was dangling into a face (not sure if this is even allowed?)
 in this case it would have originally had the same face on both sides of
 the segment... this case I could see possibly returning null.

 Forgive my lack of knowledge of the workings of the topology system, but
 what is expected to be done with the returned face id? Does the model
 itself automatically update the other edges of the now-merged faces for
 you, or is this the purpose of returning the id of the newly merged face
 (so you can manually set the face_ids of the other segments)?. Also, why
 would you care if the returned ID is newly created or previously existing
 (assuming the model creates the face and assigns it's id to the necessary
 edges) - where the segment once was, there is now a face, I think it is
 always possible to return a single face id as the result? Unless perhaps
 there is a duplicate edge (if such a thing is allowed)? This would
 definitely be a case to return null.

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/1188#comment:2>
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