[postgis-tickets] [PostGIS] #4758: ERROR: XX000: SQL/MM Spatial exception - geometry crosses edge 2, LOCATION: pg_error, lwgeom_pg.c:250

[PostGIS]

#4758: ERROR:  XX000: SQL/MM Spatial exception - geometry crosses edge 2,
LOCATION:  pg_error, lwgeom_pg.c:250
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  Reporter:  laopsahl  |      Owner:  pramsey
      Type:  defect    |     Status:  new
  Priority:  medium    |  Milestone:  PostGIS 3.1.0
 Component:  postgis   |    Version:  3.0.x
Resolution:            |   Keywords:
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Comment (by strk):

 Here's the problem: the intersection point (blue) computed between the
 existing edges (black) and the new line (red) gets snapped to the existing
 node being below tolerance.

 [[Image(intersection.png)]]

 My feeling is that the starting condition should never happen, given the
 tolerance, and the red node should have attracted the passing-by edge
 instead of leaving where it is, effectively changing the existing edge
 rather than creating a new one. Here order matters because if the smaller
 edge was inserted before, its node would have resulted in the longer edge
 snapping to it.

 At this moment, the code tries NOT to snap existing edges to new nodes, to
 avoid dealing with edge collapses (you can see, in this case, that
 snapping the existing edge to the new node would result in a collapse).

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/4758#comment:3>
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