[GRASS-dev] [GRASS GIS] #3319: v.overlay: incorrect results with "not" operator

[GRASS GIS]

#3319: v.overlay: incorrect results with "not" operator
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  Reporter:  sbl          |      Owner:  grass-dev@…
      Type:  defect       |     Status:  new
  Priority:  major        |  Milestone:  7.2.1
 Component:  Vector       |    Version:  svn-releasebranch72
Resolution:               |   Keywords:  v.overlay
       CPU:  Unspecified  |   Platform:  Unspecified
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Comment (by mmetz):

 Replying to [ticket:3319 sbl]:
 > In a project I want to clip away the sections from a river network that
 are within lakes.
 >
 > Unfortunately, some streams vanished from the result completely (which
 should not)...

 Please try v.overlay in trunk r70800.

 The problem lies with Vect_break_lines() and Vect_break_lines_list() which
 create new vertices that are sometimes too close to existing vertices
 (floating point representation error). Radim was aware of that problem in
 v.overlay. I (hopefully) fixed the symptom in v.overlay. The real fix
 would be to not use a fixed value for rethresh (Radim was also aware of
 that problem) in Vect_line_intersection() and Vect_line_intersection2(),
 but instead set rethresh to the smallest representable difference (ULP).

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Ticket URL: <https://trac.osgeo.org/grass/ticket/3319#comment:1>
GRASS GIS <https://grass.osgeo.org>