[GRASS-user] advice on interpolation

[Bulent Arikan]

Hi,

I have an ASTER GDEM (Latlong, 30 m resolution, from NASA web site) imagery.
I want to produce 10m res DEM from it. Here is what I have done and what my
problem is. I really appreciate suggestions.

- I reprojected the imagery into a UTM location (using the 'nearest'
method),
- Using 'g.region', I set my region to match the original DEM
- I set my computational extents from the display,
- then, I sampled 50% of the original imagery (in r.random) and created a
vector map (it took long time to do this and it has around 5 million points
in it),
- I set the resolution to 10 meters using 'g.region',
- then, using 'v.surf.rst', I tried to make a new DEM -10m resol- from the
sampled vector map and masking the operation with the original -30m- DEM. I
do not change the default settings and I use a smoothing parameter of '.1'
and i use the "value" column from the vector map for approximation in the
process.

I get a lot of error messages during interpolation, like;

G_ludcmp() failed! n=0
taking too long to find points for interpolation--please change the region
to area where your points are. Continuing calculations...


I am not sure but may be my region settings is wrong (i.e., too wide)
although I used the imagery to set them. I never waited for interpolation to
run completely.

Thank you for suggestions!


-- 
BÜLENT ARIKAN
School of Human Evolution and Social Change
Arizona State University
Tempe - AZ
85287-2402
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