[GRASS-dev] Re: [GRASS GIS] #994: v.buffer creating wrong buffer around polygon edges.

[GRASS GIS]

#994: v.buffer creating wrong buffer around polygon edges.
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  Reporter:  mlechner  |       Owner:  grass-dev at lists.osgeo.org
      Type:  defect    |      Status:  new                      
  Priority:  major     |   Milestone:  6.4.0                    
 Component:  Vector    |     Version:  6.4.0 RCs                
Resolution:            |    Keywords:  v.buffer                 
  Platform:  Linux     |         Cpu:  Unspecified              
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Comment (by hamish):

 > but I'm not sure about the example at the end of the old report.

 that's another thin-area one which was fixed by the v.buffer2 replacement.


 taking a hint from RT# 2765 I tried v.build.polylines on rstrct_areas and
 reran the test. interestingly the buffer comes out completely empty! (ah
 that is because cats are *completely* lost from centroids in that
 process!?.

 moving the centroids of the 2 small NW polygons into their respective
 middles with v.digit didn't help. after assigning centroids in the
 v.build.polylines output map it still breaks but a bit differently. this
 time the big area looks ok.

 we can simplify it back to a single 4 sided rectangle:
 {{{
 v.extract in=rstrct_areas out=rstrct_areas_cat4 list=4
 v.buffer in=rstrct_areas_cat4 out=rstrct_areas_cat4_buf1000 dist=1000
 }}}

 which is:
 {{{
 B  5
  598239.59422707 4917334.78591833
  598255.01958824 4916224.77709862
  599657.47540894 4916247.27752886
  599645.08933166 4917345.07553359
  598239.59422707 4917334.78591833
 C  1 1
  598825.31    4916714.37
  1     4
 }}}

 that NW corner fails even with distance=20, which makes me posture that it
 is an acute angle thing and not to do with the centroid.


 Hamish

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Ticket URL: <https://trac.osgeo.org/grass/ticket/994#comment:2>
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