[postgis-tickets] [PostGIS] #3280: Almost collinear edges prevent adding a copy of existing edge

[PostGIS]

#3280: Almost collinear edges prevent adding a copy of existing edge
-----------------------+---------------------------
  Reporter:  strk      |      Owner:  strk
      Type:  defect    |     Status:  new
  Priority:  medium    |  Milestone:  PostGIS 2.1.9
 Component:  topology  |    Version:  2.0.x
Resolution:            |   Keywords:  robustness
-----------------------+---------------------------

Comment (by strk):

 The problem is that on adding the straight line again, it first gets noded
 to existing edges with a tolerance computed based on minimum representable
 number in the floating point grid. The snapping ends up "splitting" the
 straight line where the other line goes away. Later, on adding the new
 node, existing edges gets snapped to it, and thus the existing straight
 edge is moved to intersect the other close edge.

 The solution would seem to be to not only snap existing edges to new nodes
 but also to new or modified edges. As usual this can only work
 consistently if the tolerance value is constant over all operations, and
 if the input is guaranteed to fall on that given grid.

--
Ticket URL: <https://trac.osgeo.org/postgis/ticket/3280#comment:3>
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.