[GRASS-user] r.shaded.relief visual banding

[Patrick Dolan]

Dylan, I appreciate the advice and the examples. I've succeeded in 
removing the "banding" but only though converting the a small subsection 
of the DEM into a point vector (with r.to.vect) and then back to a dem 
(with r.surf.rst).

It's a working, though suboptimal solution as it takes my Gen 1 MacBook 
(2 GB of DDR2 SDRAM and 2 Ghz Core) several hours to create the vector 
and then recreate a 1 by 1 degree DEM (the SRTM 90 tiles are 5 by 5 
degrees-which I subdivide or suffer GRASS' code 12 error).

Cheers,
Patrick

On 10-11-17 10:48 AM, Dylan Beaudette wrote:
> On Wednesday, November 17, 2010, Patrick Dolan wrote:
>> Hello all,
>> Are there known issues with "banding" in the output of the
>> r.shaded.relief command? When I say banding, I mean the generation of
>> regularly occurring, narrow vertical and horizontal lines. I've just
>> created a large shaded relief map of the northern Pacific coasts of the
>> USA and Canada from the STRM 90m v.4 Arc/Ascii files. At ~380 m
>> intervals, ~30 m bands have been generated that crisscross the output.
>> I'd like to know if this is a consequence of the STRM 90 data set
>> (notably 3DEM appears to have no similar trouble with the same data), or
>> an artifact of the shaded relief command in GRASS. I can attach an image
>> if this would help the diagnosis.
>>
>> Much appreciated,
>> Patrick Dolan
> Hi Patrick,
>
> I haven't used the SRTM data, but I have seen this happen when working with
> the USGS 10m NED. It seems like it has something to do with the projection, as
> illustrated in this somewhat dated demonstration I put together in order to
> figure out what was going on:
>
> http://169.237.35.250/~dylan/gdalwarp/image_matrix.html
>
> Here are some related messages from many years ago:
> http://www.osgeo.org/pipermail/grass-user/2006-May/034257.html
>
> I should probably update the original analysis based on some of Maciek's
> comments in that thread, and changes that have taken place since 2006.
>
> Cheers,
> Dylan
>
> --
> Dylan Beaudette
> Soil Resource Laboratory
> http://casoilresource.lawr.ucdavis.edu/
> University of California at Davis
> 530.754.7341
>