[GRASS-user] Basin DEM advice needed

Ken Mankoff mankoff at gmail.com
Wed Oct 2 23:02:33 PDT 2019

Hi Rich,

On 2019-10-03 at 00:22 +02, Rich Shepard <rshepard at appl-ecosys.com> wrote...
> Attached are two maps using 1m LiDAR data. The annotated map,
> basin-elevations.png, was drawn by individually applying d.rast to each of
> the 70 maps covering the basin. Sharp breaks can be seen where the data
> cross quads or flights didn't match up smoothly.
> The un-annotated map, nehalem-dem-patched.png, displays the results of
> running r.patch on all 70 maps. Topographically it's quite different from
> the individual maps; almost flat when the north, east, and south edges
> should have elevations similar to the other map.

The two maps are showing the same data. d.rast scales each raster to (min,max) of the colorbar, which is why the tiles appear misaligned. The data is unchanged.

> I think I should apply r.resamp.stats to aggregate the 1m resolution
> to 5m. I'd like your thoughts on this.

I don't see how anyone can answer that without knowing the specifics of your project and goals.

> I assume that I should resample each individual map, then re-run
> r.patch on the coarser maps because r.slope.aspect and r.info need a
> single map as input.

I'd patch than resample to avoid possible edge effects, if your resample isn't perfectly aligned with each sub-raster.


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