[GRASS-dev] [GRASS GIS] #2101: Different results from m.proj in different locations

[GRASS GIS]

#2101: Different results from m.proj in different locations
---------------------------------+---------------------------------
  Reporter:  wenzeslaus          |      Owner:  grass-dev@…
      Type:  defect              |     Status:  new
  Priority:  normal              |  Milestone:  7.4.0
 Component:  Projections/Datums  |    Version:  svn-trunk
Resolution:                      |   Keywords:  m.proj, projections
       CPU:  Unspecified         |   Platform:  Unspecified
---------------------------------+---------------------------------

Comment (by mmetz):

 Replying to [comment:4 neteler]:
 > I just made a new test here:
 >
 > {{{
 > # part 1:
 > GRASS 7.4.0svn (nc_spm_08_grass7):~/grassdata > eval $(r.info
 map=elevation -g)
 > GRASS 7.4.0svn (nc_spm_08_grass7):~/grassdata > m.proj -o -d input=-
 separator=space <<EOF
 > > $east $north
 > > $west $south
 > > EOF
 > -78.60830318 35.80918894 0.00000000
 > -78.77462049 35.68792712 0.00000000
 >
 > g.version -reg
 > version=7.4.0svn
 > date=2018
 > revision=r72020
 > build_date=2018-01-04
 > build_platform=x86_64-pc-linux-gnu
 > build_off_t_size=8
 > libgis_revision=70829
 > libgis_date="2017-04-04 09:43:02 +0200 (Tue, 04 Apr 2017) "
 > proj4=4.9.3
 > gdal=2.1.3
 > geos=3.6.1
 > sqlite=3.20.1
 > }}}
 >
 > Then:
 >
 > {{{
 > # part 2:
 > GRASS 7.4.0svn (TEST):~/grassdata > g.proj -w
 > PROJCS["WGS 84 / Pseudo-Mercator",
 >     GEOGCS["unnamed",
 >         DATUM["unknown",
 >             SPHEROID["unnamed",6378137,"inf"]],
 >         PRIMEM["Greenwich",0],
 >         UNIT["degree",0.0174532925199433]],
 >     PROJECTION["Mercator_2SP"],
 >     PARAMETER["standard_parallel_1",0],
 >     PARAMETER["central_meridian",0],
 >     PARAMETER["false_easting",0],
 >     PARAMETER["false_northing",0],
 >     UNIT["Meter",1]]
 >
 > eval $(r.proj -g input=elevation location=nc_spm_08_grass7
 mapset=PERMANENT)
 >
 > m.proj -o -d input=- separator=space <<EOF
 > > $e $n
 > > $w $s
 > > EOF
 > -78.60830318 35.80960938 0.00000000
 > -78.77462049 35.68750730 0.00000000
 >
 > # expected (?)
 > -78.60830318 35.80918894 0.00000000
 > -78.77462049 35.68792712 0.00000000
 > }}}

 No, not expected: first you reproject the upper-right corner and the
 lower-left corner with `m.proj`. Then you run `r.proj -g` which reprojects
 all outer corners of all border cells to figure out the new extents. This
 test assumes that a rectangle stays a rectangle after reprojection and
 that north of the upper-left and upper-right corner are the same after
 reprojection (not to mention northing of points in between the upper-left
 and upper-right corner). This assumption is wrong.

 EPSG:3857 (WGS 84 Pseudo-Mercator) is now handled reasonably well in 7.4
 and 7.5, as long as the location is newly created to get correct
 projection information.

--
Ticket URL: <https://trac.osgeo.org/grass/ticket/2101#comment:5>
GRASS GIS <https://grass.osgeo.org>