[GRASS-user] High resolution dem

[John Tate]

On Sunday 28 February 2010 02:15:45 Hamish wrote:
> John Tate wrote:
> > and then patched (r.patch) them all together. The patching should
> > average out any differences.
> 
> r.patch doesn't average, it uses the cell from the first-listed raster
> map which contains a non-NULL cell. Later-listed rasters fill in the gaps
> until there are no more gaps or no more maps. r.series will merge
> overlapping maps using an average though.

Yeah, my mistake, again! Keep confusing those two.
 
> > I then cropped out each 1km tile (1000x1000).
> > This was done so that the 1km tiles could be combined for specific
> > areas by different people (e.g. only a 4kmsq area for academic 'a' or a
> > 6kmsq area 2km away for academic 'b').
> 
> why not just use g.region for that?

Interoperability. So they can be used in ArcGIS, MapInfo, IDRISI and TAS by 
various people (after export as ESRI Grid).

> Nick Cahill wrote:
> > I was never able to get the parameters right in *.surf.rst, and
> > processing times were very long.
> 
> True & true. "auto-tune" has been a wish for a while. it probably would
> take a while to run though. maybe the tips on the RST Spline Surfaces
> wiki page along with the ones on the main help page can be useful?
> The results can be very nice once you get it tuned right though.

Nice script here for cross validation:
http://lists.osgeo.org/pipermail/grass-user/2007-May/039530.html
I used a smaller area, e.g. 100x100 cell area, that is representative of the 
terrain to speed things up.

John