[GRASS-user] Re: advice on interpolation

madi diregola at gmail.com
Wed Mar 31 04:35:27 EDT 2010

Hi Bulent,
First of all, what OS are you using? What grass version?
You can try with a smaller percentage of points in r.random and/or in 
v.surf.rst try increasing dmin (it's the distance of points to take into 
account in the interpolation).


> 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!

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