[GRASS-user] interpolating images with coastal areas

Bulent Arikan bulent.arikan at gmail.com
Sun Mar 20 14:03:35 EDT 2011

Dear List,

I am working on interpolating 30m ASTER DEMs to 10m resolution. I am using
GRASS 6.4.1 svn on Mac OS 10.6.6. Since the imagery covers a large area, I
crop the 30m DEM into individual tiles in order to make the project more
manageable. The interpolation process (using v.surf.rst) has been working
fine and the values in resultant 10m DEMs have been quite accurate,
especially for inlands. However, I have some problems with interpolating
tiles where coastline is present. In these tiles, the range of values in 10m
DEMs go below zero. In some cases I have values such as -21 meters whereas
the original –30m– tiles have only zero. Obviously, I am concerned about the
accuracy of the end product.

Do I get high negative values because of the cells with zero value?

Should I zoom further in and avoid having zero-value cells? (which is a
problem with coastlines where they are not straight)

Does any one have a suggestion about how to deal with this problem?

* I sample the original imagery at 50% in r.random,

* I use the default parameter values in v.surf.rst (tension= 40.) and use
the 30m DEM as MASKMAP,

* I align region to resolution, using g.region.


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