[GRASS-dev] [GRASS GIS] #3680: [PATCH] r.object.geometry: add output of mean coordinates of objects - difference to r.mapcalc/r.univar output

[GRASS GIS]

#3680: [PATCH] r.object.geometry: add output of mean coordinates of objects -
difference to r.mapcalc/r.univar output
------------------------------------------------+-------------------------
 Reporter:  mlennert                            |      Owner:  grass-dev@…
     Type:  enhancement                         |     Status:  new
 Priority:  normal                              |  Milestone:
Component:  Addons                              |    Version:  unspecified
 Keywords:  r.object.geometry cell coordinates  |        CPU:  Unspecified
 Platform:  Unspecified                         |
------------------------------------------------+-------------------------
 For some applications it can be useful to obtain the mean coordinates of
 raster objects. I would like to add this functionality to
 r.object.geometry. For this I use the attached patch.

 However, when I use this to calculate mean coordinates of objects, I get
 one unit of resolution difference between these results and the results of
 the following r.mapcalc/r.univar call:


 {{{
 g.region rast=MyMap
 r.mapcalc "x = x()"
 r.univar -t x zones=MyMap
 }}}

 Here's some output for comparison:


 {{{
 r.mapcalc/r.univar      r.object.geometry

 zone|mean               cat|mean_x
 1|270347.103514056      1|270347.353514
 2|270355.499712833      2|270355.749713
 3|270243.128030303      3|270243.378030
 4|270270.053380443      4|270270.303380
 5|270280.90239726       5|270281.152397
 6|270277.778301887      6|270278.028302
 }}}

 The result of r.object.geometry is always shifted one resolution (0.25) to
 the East.

 However, y values are not:


 {{{
 r.mapcalc/r.univar      r.object.geometry

 zone|mean               cat|mean_x
 1|154056.164959839      1|154056.164960
 2|153996.903084224      2|153996.903084
 3|154041.199242424      3|154041.199242
 4|154016.742456073      4|154016.742456
 5|154017.476598174      5|154017.476598
 6|154017.057193396      6|154017.057193
 }}}

 Is the error in my patch, or maybe in the r.mapcalc x() function ?

 Any objections to applying this patch ? It changes the output of the
 module, but it add the additional values at the end, so unless some
 scripts rely on fd being the last value, this should not cause too much
 trouble.

 Moritz

-- 
Ticket URL: <https://trac.osgeo.org/grass/ticket/3680>
GRASS GIS <https://grass.osgeo.org>