[GRASS-user] r.shaded.relief Output Question

[Daniel Lee]

Hi Rich,

I can't imagine that resampling would reverse the DEM values though. A
glance at r.info would give you the answer to that - if the values are
mostly negative, it should be a pretty good sign that you're either in
Death Valley or inverted :P

One thing to note with r.shaded.relief though is that it doesn't use the
GRASS convention for solar azimuths. NOAA, for example, tells azimuths in
degrees clockwise from north, but GRASS normally uses degrees
counterclockwise from east. r.shaded.relief follows the NOAA system, but
either way, 235° would be in just around the same place for both systems
(as odd as that is). The sun would be coming from the southwest. When I
look at your map (wish the resolution was a bit higher) it looks like the
sun very well could be coming from that direction (I'm just using the
rivers as orientation for relative height). Have you tried another angle,
like taking a look at what the map looks like if the sun's shining from
180° (due south)?

Best,
Daniel

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Am 23. März 2012 17:12 schrieb Rich Shepard <rshepard at appl-ecosys.com>:

>  Running r.shaded.relief on a 10m DEM with alt=30, azimuth=235 (the basins
> are near the US-Canadian border), and zmult=2, the output looks reversed to
> me (see attached .pdf). The stream channels appear to run along ridge lines
> rather than valley floors, and the basin boundaries seem to be in the
> valleys.
>
>  The source map was resampled to 30 US Feet cell resolution from the
> original 1 US Foot cell resolution using r.resamp.stats after 'g.region
> res=30 -ap'. Might I inadvertently inverted the elevations when I coarsened
> the resolution?
>
>  Suggestions and recommendations, please.
>
> Rich
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