[GRASS-user] r.contour fails to create contours on large dataset

GRASS GRASS user
1

Hi all,

I'm working on a Grass 7 python module to create a local relief model
from lidar derived DTMs. I've tested the module on small and medium
size rasters with less than 200 million cells, and the script returns
results (whether or not the results are correct is another matter).
However, when I try to run the script on an entire county with 2.5
billion cells, all of the steps up to extracting the contours from the
difference between the DTM and the low pass filter work correctly, but
the resulting contours vector is empty, causing the remainder of the
script to fail.

I know I'm short on technical details, but any input into why this
might be happening would be appreciated. The full script is located
here: http://pastebin.com/DudYK0Se

The command used to run r.contours:
grass.run_command("r.contour", input=lp_subtract, output=LP_contour,
minlevel=0, maxlevel=0, step=10)

Thanks,
Eric

2

Eric wrote:

The command used to run r.contours:
grass.run_command("r.contour", input=lp_subtract,
output=LP_contour, minlevel=0, maxlevel=0, step=10)

minlevel and maxlevel are the same?

Hamish

3

Yes, only the zero contours are needed. They represent the macro topography which are later reinterpolated and subtracted from the original DTM.

It works when testing in a smaller region, so I don’t think that is the issue…

On Mar 8, 2013 4:43 PM, “Hamish” <hamish_b@yahoo.com> wrote:

Eric wrote:

The command used to run r.contours:
grass.run_command(“r.contour”, input=lp_subtract,
output=LP_contour, minlevel=0, maxlevel=0, step=10)

minlevel and maxlevel are the same?

Hamish