[GRASS-user] Polar projection

[Markus Neteler]

Hi Ken,

On Thu, Dec 31, 2020 at 3:06 AM Ken Mankoff <mankoff at gmail.com> wrote:
>
> Dear GRASS List,
>
> Can someone suggest what setup to use (EPSG code? proj4 code?) to have the projection centered on the N. pole? I'm looking to create a graphic similar to this image in the Raster Gallery: https://grass.osgeo.org//images/gallery/raster/day_on_earth_N.png
>
> If I set up a polar projection based on https://spatialreference.org/ref/sr-org/8243/ using:
>
> grass -c ./G
> g.proj -c proj4="+proj=stere +lat_0=90 +lat_ts=45 +lon_0=-170 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs"
>
> Things mostly work, but
>
> d.grid -g 1:0 color=red
>
> does not show latitude lines on most of the graphic (see attached).

I managed to generate it with

Preparation of a 10 degree grid:

# EPSG:4326
GRASS :~ > g.region -dp
projection: 3 (Latitude-Longitude)
zone:       0
datum:      wgs84
ellipsoid:  wgs84
north:      90N
south:      90S
west:       180W
east:       180E
nsres:      1
ewres:      1
rows:       180
cols:       360
cells:      64800
GRASS :~ > v.mkgrid grid=36,18 map=grid_10deg
# download "Natural Earth I with Shaded Relief, Water, and Drainages"
from http://www.naturalearthdata.com/downloads/10m-raster-data/10m-natural-earth-1/
GRASS :~ > r.import in=NE1_HR_LC_SR_W_DR.tif
output=natural_earth_global_landcover
GRASS :~ > g.region raster=natural_earth_global_landcover.1
GRASS :~ > r.composite r=natural_earth_global_landcover.1
g=natural_earth_global_landcover.2 b=natural_earth_global_landcover.3
out=natural_earth_global_landcover.rgb
GRASS :~ > exit

# WGS 84 / Arctic Polar Stereographic https://epsg.io/3995
grass78 -c epsg:3995 ~/grassdata/arctic_polar_stereographic
GRASS :~ > g.proj -w
PROJCS["WGS 84 / Arctic Polar Stereographic",
    GEOGCS["WGS 84",
        DATUM["WGS_1984",
            SPHEROID["WGS 84",6378137,298.257223563,
                AUTHORITY["EPSG","7030"]],
            AUTHORITY["EPSG","6326"]],
        PRIMEM["Greenwich",0,
            AUTHORITY["EPSG","8901"]],
        UNIT["degree",0.0174532925199433,
            AUTHORITY["EPSG","9122"]],
        AUTHORITY["EPSG","4326"]],
    PROJECTION["Polar_Stereographic"],
    PARAMETER["latitude_of_origin",71],
    PARAMETER["central_meridian",0],
    PARAMETER["false_easting",0],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AXIS["Easting",SOUTH],
    AXIS["Northing",SOUTH],
    AUTHORITY["EPSG","3995"]]

GRASS :~ > g.region n=2930000 s=-2500000 w=-4250000 e=4310000
nsres=10000 ewres=10000 -p
GRASS :~ > v.proj location=latlong_wgs84 mapset=PERMANENT input=grid_10deg
GRASS :~ > r.proj location=latlong_wgs84 mapset=PERMANENT
input=natural_earth_global_landcover.rgb
GRASS :~ > d.mon wx0
GRASS :~ > d.rast natural_earth_global_landcover.rgb
GRASS :~ > d.vect grid_10deg type=boundary

The resulting map looks as attached (hope I didn't forget to copy a
command here).
Indeed, d.grid doesn't looks as expected

GRASS :~ > d.grid 10 -w
.. is incomplete. Worth a bug report, IMO.

Cheers,
Markus

-- 
Markus Neteler, PhD
https://www.mundialis.de - free data with free software
https://grass.osgeo.org
https://courses.neteler.org/blog
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