[PostGIS] #6121: Adding a node below distance of multiple edge segments snaps only one of them

[PostGIS]

#6121: Adding a node below distance of multiple edge segments snaps only one of
them
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 Reporter:  strk        |      Owner:  strk
     Type:  defect      |     Status:  new
 Priority:  medium      |  Milestone:  PostGIS 3.5.7
Component:  topology    |    Version:  3.5.x
 Keywords:  robustness  |
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 Starting in PostGIS-3.5.0 we added experimental code to snap more than one
 existing edges to incoming nodes when those edges are below tolerance.

 Previously, only the closest edge was snapped, to avoid having to deal
 with edge merging.

 This code is still experimental as of current master branch
 (3.7.0rc1-20-g655fc78a1) and has a known bug: if the SAME edge has
 MULTIPLE segments within tolerance distance from the incoming node only
 one of them will snap, instead of both of them.

 This limitation results in the best case in producing a resulting topology
 with unwanted proximities. In the worst case the unwanted proximities
 result in a later (possibly within same transaction) exception being
 thrown.

 A simple test to reproduce this would be:

    1. Add a V-shaped 2 segments edge, with a narrow angle
    2. Add a Point far from any of the 3 vertices of the edge but within
 tolerance from the two segments

 The correct result should be to have an Y-shaped 3 edges resulting
 topology. At the moment you are likely to get a 2 edges topology instead.
-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/6121>
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