[GRASS-dev] [GRASS GIS] #3567: v.select: doubtful result with the default overlap operator selecting areas with lines

GRASS GIS trac at osgeo.org
Tue May 29 06:27:52 PDT 2018

#3567: v.select: doubtful result with the default overlap operator selecting areas
with lines
  Reporter:  mlennert     |      Owner:  grass-dev@…
      Type:  defect       |     Status:  closed
  Priority:  normal       |  Milestone:  7.4.2
 Component:  Vector       |    Version:  svn-trunk
Resolution:  fixed        |   Keywords:  v.select overlap
       CPU:  Unspecified  |   Platform:  Unspecified

Comment (by mmetz):

 Replying to [comment:4 mlennert]:
 > Replying to [comment:3 mmetz]:
 > > Replying to [ticket:3567 mlennert]:
 > > > Trying to select areas with lines, I get a result using the overlap
 operator that I don't really understand, and which I suspect being a bug.
 > > >
 > > > Using the following command in the attached location, test_vselect
 > > >
 > > > {{{
 > > > v.select ain=test_polys bin=test_line atype=area btype=line
 out=result_overlap op=overlap
 > > > }}}
 > > >
 > > > I get a result of only three areas selected (see attached map)
 where, IMHO, all 41 should be.
 > > >
 > > The problem was not the overlap operator of v.select, but instead that
 the vector test_line is 3D, and one of the underlying library functions
 did not ignore z as it should have done. This bug has been fixed in trunk
 and relbr74 with r72746,7.
 > Thanks a lot ! Sorry, should have noticed the 3D nature of the vector
 myself. I guess there must have been a message at import which I didn't
 > This obviously raises the question of whether v.select should always
 ignore 3D or whether a flag (-3) should allow enabling it so that if one
 wants to check spatial relation in 3D this is possible.

 This is not possible because `Vect_segment_intersection()` does not
 support 3D coordinates.

 Also note that 3D topology does not exist yet in GRASS, e.g. a purely
 vertical line can cause problems, because it is marked as degenerate at
 the corresponding nodes.

Ticket URL: <https://trac.osgeo.org/grass/ticket/3567#comment:5>
GRASS GIS <https://grass.osgeo.org>

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