[GRASS-user] Elevation/bathymetry raster maps

GRASS GRASS user
1

Looking at the raster and raster addon modules I don't see one that will
allow more elevation/depth 'slices' for a given range. r.resample appears to
reduce the 'slices'; can it be used to also increase the number?

A related question is how GRASS sets the 'slice' range for assignment to a
color in the spectrum (elevation and water in these cases).

Specifically, I have a raster map with a range of depth/elevation altitudes
from -32.55505 to 595.1976 feet. Can I determine the number of 'slices'
within that range and use the water colors from minimum to zero and the
elevation colors from 1 to maximum? I want to display higher resolution in
the depths and the adjacent terrestrial elevations with a greater range of
colors to better communicate the channel and immediate river bank topology.

TIA,

Rich

2

One option always is to set colours manually.

Māris.

2021-09-29 19:12 GMT+03:00, Rich Shepard <rshepard@appl-ecosys.com>:

Looking at the raster and raster addon modules I don't see one that will
allow more elevation/depth 'slices' for a given range. r.resample appears
to
reduce the 'slices'; can it be used to also increase the number?

A related question is how GRASS sets the 'slice' range for assignment to a
color in the spectrum (elevation and water in these cases).

Specifically, I have a raster map with a range of depth/elevation altitudes
from -32.55505 to 595.1976 feet. Can I determine the number of 'slices'
within that range and use the water colors from minimum to zero and the
elevation colors from 1 to maximum? I want to display higher resolution in
the depths and the adjacent terrestrial elevations with a greater range of
colors to better communicate the channel and immediate river bank topology.

TIA,

Rich
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/grass-user

3

On Thu, 30 Sep 2021, Maris Nartiss wrote:

One option always is to set colours manually.

Māris,

That occurred to me: use r.mapcalc to define ranges of depth/elevation then
assign a color to each.

Thanks,

Rich

4

Am 30.09.2021 14:40 schrieb Rich Shepard:

On Thu, 30 Sep 2021, Maris Nartiss wrote:

One option always is to set colours manually.

Māris,

That occurred to me: use r.mapcalc to define ranges of depth/elevation then
assign a color to each.

No need for r.mapcalc if what you are looking for is coloring. Just define a color table definition file and feed it to r.colors.

This color table file can be quite flexible, e.g. to get more differentiated coloring between -5000 and -3000, you can use something like this:

-5000 0:0:0
- 4000 50:50:50
- 3000 100:100:100
0 175:175:175
100% 255:255:255

Check the r.colors man page for more details.

Moritz

5

On Thu, 30 Sep 2021, Moritz Lennert wrote:

No need for r.mapcalc if what you are looking for is coloring. Just define
a color table definition file and feed it to r.colors.

This color table file can be quite flexible, e.g. to get more differentiated coloring between -5000 and -3000, you can use something like this:

-5000 0:0:0
- 4000 50:50:50
- 3000 100:100:100
0 175:175:175
100% 255:255:255

Check the r.colors man page for more details.

Moritz,

Thank you. I will.

Regards,

Rich