[GRASS-user] r.shade.relief: Results Not As Expected

[Glynn Clements]

Rich Shepard wrote:

> > Run r.slope.aspect on the interpolated map, and check for grid-like
> > artifacts.
> 
> Glynn,
> 
>    Did this. Yes, there is a grid-like appearance to the resulting map.
> 
> > How good is the underlying data? If it's noisy, it may need to be
> > filtered before interpolating.
> 
>    How do I check for noisy data? I have all the basic information about the
> source data and derived maps.

One trick is to create a filtered map with e.g. r.neighbors
method=average or r.mfilter.fp, and subtracting the original map from
the resulting map. This will help to highlight any artifacts
introduced by processing of the source data.

Any such processes should be performed at the map's native resolution,
to ensure that artifacts aren't introduced by nearest-neighbour
resampling.

One thing which can introduce grid-like artifacts is nearest-neighbour
resampling (including re-projection) at near-unity scale factors.

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