[GRASS-dev] [GRASS GIS] #3860: GRASS GIS producing different slope than GDAL

[GRASS GIS]

#3860: GRASS GIS producing different slope than GDAL
------------------------+-------------------------
  Reporter:  mazingaro  |      Owner:  grass-dev@…
      Type:  defect     |     Status:  new
  Priority:  major      |  Milestone:  7.6.2
 Component:  Raster     |    Version:  unspecified
Resolution:             |   Keywords:  slope
       CPU:  x86-64     |   Platform:  Linux
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Comment (by mankoff):

 I think the issue is related to the region.

 The `r.slope.aspect` documentation in the NOTES section implies that the
 region is adjusted to the raster. I do not find that to be the case.
 Specifically in the NC test data, I've created the following slope
 rasters, and then looked at their univariate statistics:

 {{{
 g.region raster=elevation
 r.slope.aspect elevation=elevation slope=slope_0
 r.slope.aspect -a elevation=elevation slope=slope_1
 g.region res=30 -pa
 r.slope.aspect elevation=elevation slope=slope_2
 r.slope.aspect -a elevation=elevation slope=slope_3

 for i in $(seq 0 3); do
   (echo -n "slope_${i} "; r.univar slope_${i} | grep range) | tr '\n' ' '
 done
 }}}

 Results are:

 {{{
 slope_0 range: 36.3347
 slope_1 range: 36.3347
 slope_2 range: 13.7754
 slope_3 range: 25.3968
 }}}

-- 
Ticket URL: <https://trac.osgeo.org/grass/ticket/3860#comment:9>
GRASS GIS <https://grass.osgeo.org>