[postgis-tickets] [PostGIS] #3380: "geometry crosses edge" with 1e-2 tolerance

[PostGIS]

#3380: "geometry crosses edge" with 1e-2 tolerance
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  Reporter:  strk      |      Owner:  strk
      Type:  defect    |     Status:  new
  Priority:  medium    |  Milestone:  PostGIS 2.0.8
 Component:  topology  |    Version:  2.0.x
Resolution:            |   Keywords:
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Comment (by strk):

 From the logs, it is interesting to see that the input line (cyan above)
 snapped to the existing edges (all the rest) results in a line which
 extends to the existing node 4.
 Not that this should by itself matter at this stage, but it is something
 to keep in mind:
 {{{
 -- Snapping line to existing edges adds the overlapping segment
 [lwt_AddLine:5559] Snapped:
 LINESTRING(1612830.15444847 4841287.1267168,1612830.15823523
 4841287.12674008,1612881.64990281 4841274.56198261)
 }}}

 Of further noding, we end up with a multilinestring formed by the two
 components: new line, overlapping line.

 Now next step is snapping again this obtained multilinestring to the
 existing _NODES_.
 This time we only have the node to snap against, which is below tolerance.
 There is no edge vertex anymore to snap against, so the result is that
 while the overlapping line remains unchanged (one endpoint is already on
 the node), the other one gets his endpoint moved on the node too,
 introducing the crossing (with edge 4 in the picture below):

 [[Image(crossing.png)]]

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/3380#comment:7>
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