[GRASS-user] Reprojecting to x,y grid

[Moritz Lennert]

On 18/11/20 15:01, Ken Mankoff wrote:
> Hello,
> 
> On 2020-11-17 at 10:06 -08, Ken Mankoff <mankoff at gmail.com> wrote...
>> I've successfully worked in rotated pole coordinates (e.g., [1]) but
>> because I don't know what (x,y) coord contains the pole, I haven't
>> figured out how to adapt this to the rotated pole situation as in [1].
>> Anyway, this isn't a rotated pole...
> 
> I was incorrect - this is a rotated pole coordinate system.
> 
> When I run the following code on GRASS 7.4, I get the attached graphic. The key part here is that the rotated pole is at (lon,lat) = (-200,18).
> 
> 
> 
> grass -c EPSG:4326 Gnorm
> 
> # Import something into the normal location
> v.import input=~/data/Zwally_2012/sectors output=Z
> 
> cat << EOF > ./Gnorm/PERMANENT/PROJ_INFO
> name: General Oblique Transformation
> datum: wgs84
> towgs84: 0.000,0.000,0.000
> proj: ob_tran
> o_proj: latlon
> ellps: wgs84
> a: 6378137.0000000000
> es: 0.0066943800
> f: 298.2572235630
> lat_0: 0.0000000000
> lon_0: 180.0000000000
> o_lat_p: 18.0
> o_lon_p: -200.0
> EOF
> 
> # rotated_pole:grid_north_pole_latitude = 18. ;
> # rotated_pole:grid_north_pole_longitude = -200.
> 
> cat << EOF > ./Gnorm/PERMANENT/PROJ_UNITS
> unit: degree
> units: degrees
> meters: .0174532925
> EOF
> 
> grass -e -c EPSG:4326 Grot
> grass ./Grot/PERMANENT
> 
> v.proj location=Gnorm input=Z
> g.region vector=Z
> 
> d.mon start=wx0
> d.vect Z
> d.grid 1:0:0
> 
> 
> The above code run in GRASS 7.4.0 on a clean Ubuntu 18.04 VM produces the attached graphic. However, when I run the exact same code in GRASS 7.8.4 it does not work. The reproject/rotate does not occur, and Greenland remains at 62-82 N, and 22-72 W.
> 
> The contents of the "Gnorm" folders is appears identical. The md5sum of DEFAULT_WIND, MYNAME, PROJ_EPSG, PROJ_INFO, and PROJ_UNITS are all the same.
> 
> I can do the work in GRASS 7.4 in a VM but I'd prefer to do it on the main development machine in the latest GRASS. Does anyone have any idea why this feature stopped working?

Maybe because of changes linked to proj6 support ? Markus Metz will know.

Moritz



Moritz