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

[Glynn Clements]

Patrick Dolan wrote:

> 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.

First, ensure that the region matches the map. nearest-neighbour
resampling will introduce artifacts in anything which calculates
derivatives.

Second, ensure that the source data is good. The simplest way to do
this is to run r.slope.aspect on the map and visually examine the
resulting slope map.

-- 
Glynn Clements <glynn at gclements.plus.com>