[GRASS-user] patching dems together

Markus Metz markus.metz.giswork at googlemail.com
Thu Jul 9 14:50:54 EDT 2009

stephen sefick wrote:
> I followed the directions all set to srtm, computation region set to
> resolution of the coarsest (they are all the same and 00:00:01).  The
> map is still coming out as 7 different solid color blocks.
You have set the region to include all tiles? You have zoomed to the
current region? The patched DEM still ranges from 0-296 only and not
from 9-800 (r.info -r)?

I've done that regularly with SRTM tiles and it worked, no problems
> On Thu, Jul 9, 2009 at 12:58 PM, Markus
> Metz<markus.metz.giswork at googlemail.com> wrote:
>> stephen sefick wrote:
>>> values range from ~-9 to ~800 there is a tile which has no elevation.
>>> The patched dem only ranges from 0-296.  This may be the problem.
>> It seems that the current computational region did not include all tiles.
>> Try setting the computational region to include all tiles with g.region
>> rast=<all your tiles>.
>> Check the resolution of each tile with r.info -s. If they are not all
>> the same, use the coarsest resolution to be safe.
>> Check the resolution of the computational region. It must be the same
>> like the coarsest resolution, if not, set it to that.
>> Set the same color rules for all tiles. Use srtm or etopo2 but not
>> elevation because elevation will be different for each tile.
>> Display all tiles, zoom to the computational region.
>> Patch all tiles.
>> Set the same color rules to the patched DEM like to the tiles.
>> Add the patched DEM to the display, it should look like the previous
>> display with all the tiles.
>> Good luck,
>> Markus M

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