[GRASS-dev] [GRASS GIS] #2648: v.concave.hull fails with small number of points

[GRASS GIS]

#2648: v.concave.hull fails with small number of points
--------------------------+--------------------------
  Reporter:  annakrat     |      Owner:  grass-dev@…
      Type:  defect       |     Status:  new
  Priority:  normal       |  Milestone:  7.0.1
 Component:  Addons       |    Version:  unspecified
Resolution:               |   Keywords:  concave hull
       CPU:  Unspecified  |   Platform:  All
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Comment (by annakrat):

 Replying to [comment:5 mlennert]:
 > Replying to [comment:3 mlennert]:
 > > Replying to [ticket:2648 annakrat]:
 > > > Tested with 3, 4, 5 points, v.concave.hull fails. Depends on
 threshold and point configuration, too.
 > > >
 > > > {{{
 > > > ERROR: Input vector map contains no boundaries.
 > > > ...
 > > >  ['v.centroids', '--q',
 'input=concave_hull_tmp_31390_delaunay_borders_select',
 'output=concave_hull_tmp_31390_delaunay_areas_select'] ended with error
 > > > }}}
 > >
 > > AFAICT, the algorithm cannot calculate the hull because the threshold
 is too high. For now I've added a fatal error in the script with a hint
 about the threshold (r65495).
 >
 > I've changed it again in r65496: the algorithm now automatically reduces
 the threshold if it is too high and only fatals out if even a threshold of
 0 wouldn't work.

 Thanks, this works for the case. But for some point configurations, the
 algorithm still doesn't produce what I would expect, for example these
 points where the concave and convex hull should be the same I think, but
 are not:

 {{{
  echo "638597|220531
 638838|220526
 638757|220237
 638606|220331
 638651|220576.08
 638735|220601.28
 638798|220578.18
 638856.8|220456.38
 638886.2|220292.58
 638644.7|220256.88
 638579.6|220437.48" | v.in.ascii in=- out=points --o
  v.concave.hull input=points out=hull --o
 }}}

 I don't know what could be done about it. Maybe we could consider this
 ticket as solved. Thank you

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2648#comment:6>
GRASS GIS <http://grass.osgeo.org>