[GRASS-user] Problem with g.region in lat-lon projection

[Moritz Lennert]

On 28/11/11 13:23, John A Stevenson wrote:
> Hi,
>
> I am trying to set up a grid with a specified resolution using
> g.region. The information about the grid that came with the data that
> I want to plot is: X grid origin: 0.2812500 Y grid origin: -89.81250
> X grid size: 640 Y grid size: 480 X grid resolution: 0.5625000 Y grid
> resolution: 0.3750000
>
> I set up the grid with the following command:
>
> GRASS 6.4.1 (global_ll_wgs84):~/NAME/G2011 > g.region w=0.2812500
> s=-89.81250 cols=640 rows=480 ewres=0.562500 nsres=0.3750000
>
> I would expect this grid to cover the whole globe (e.g.
> 640*0.5625=360), but instead it just generates a thin strip, and the
> ewres is too small.
>

If you have existing settings for e and n, it will keep those. You have
to use g.region -d to reset to default values (assuming your default 
values are -180 - 180 & -90 - 90).

However, I think that g.region maxes out at 180E and 90N. When I use
your settings, I get the following:

GRASS 6.4.1 (LLWGS84):~ > g.region -d w=0.2812500 s=-89.81250 cols=640
rows=480 ewres=0.562500 nsres=0.3750000 -p
projection: 3 (Latitude-Longitude)
zone:       0
datum:      wgs84
ellipsoid:  wgs84
north:      90N
south:      89:48:45S
west:       0:16:52.5E
east:       180E
nsres:      0:22:28.59375
ewres:      0:16:50.917969
rows:       480
cols:       640
cells:      307200

or by aligning to resolution:

GRASS 6.4.1 (LLWGS84):~ > g.region -d w=0.2812500 s=-89.81250 cols=640
rows=480 ewres=0.562500 nsres=0.3750000 -pa
projection: 3 (Latitude-Longitude)
zone:       0
datum:      wgs84
ellipsoid:  wgs84
north:      90N
south:      90S
west:       0
east:       180E
nsres:      0:22:30
ewres:      0:16:52.5
rows:       480
cols:       640
cells:      307200

i.e. it adapts the resolution in order to get 640 columns between 0W and 
180E.

Moritz