[GRASS-user] creating high-resolution DMT

[Benjamin Ducke]

On 21/03/17 10:12, Blumentrath, Stefan wrote:
> Hei Martin,
> 
> Same experience here. For larger datasets from LiDAR I rather use IDW
> for interpolation.

I just realized that I have never committed "r.fill.gaps"
to the add-ins repo.

I have just done that now:

http://grasswiki.osgeo.org/wiki/AddOns/GRASS_6#r.fill.gaps

Its purpose is filling small gaps in otherwise dense
data using IDW with a pre-computed weights matrix.
It works on rasterized data, so you simply use v.to.rast
on your vector points first. Make sure to set the
cell size small enough so that you don't get many
vector points falling into the same cell. The result
will be an oversampled raster with a lot of small
"no data" cells. That's exactly the intended input for
r.fill.gaps!

This is not multi-core code, (parallelizing
interpolation algorithms is hard, because you need to
segment the data and then you need to deal with the
seams between the segments), but it is very, very fast,
as long as you keep the IDW radius small.

The code is optimized to death, which makes it very
hard to read. Another drawback is that it was written
for GRASS 6 (but converting it to GRASS 7 should not
be hard, since it uses only the basic raster API).

r.fill.gaps is not useful for filling large gaps, both
in terms of performance (for large IDW radii) and
interpolation quality (it's IDW -- enough said).

Best,

Ben

> 
> The "per hole filling" in r.fillnulls is not utilizing multiple cores
> and if you have a lot of holes that can slow down the whole process
> significantly. Not sure if a mask can help to avoid filling no data
> areas around your data.
> 
> For r.fillnulls there is an enhancement ticket (with a patch) for
> speedup of the patching of the maps at the end... 
> https://trac.osgeo.org/grass/ticket/1938 However, it does not tackle
> parallel filling of holes...
> 
> Cheers Stefan
> 
> _______________________________________________ grass-user mailing
> list grass-user at lists.osgeo.org 
> https://lists.osgeo.org/mailman/listinfo/grass-user
> 



-- 
Dr. Benjamin Ducke
{*} Geospatial Consultant
{*} GIS Developer

Spatial technology for the masses, not the classes:
experience free and open source GIS at http://gvsigce.org