[GRASS-user] interpolating images with coastal areas
Edgar Pimiento
e_pimiento at yahoo.com
Sun Mar 20 18:14:40 EDT 2011
Hi,
The problem is probably the data for the sea of the ASTER images. In some cases
I have seen negative values for sea areas and extremely high values, errors
also, in mountainous areas. For interpolating I think it is better to treat the
sea areas as no data values. Use the land area as mask in the interpolation. You
can also check the ASTER elevation data comparing with the corrected version of
90-m SRTM from http://srtm.csi.cgiar.org/
Best,
Edgar Pimiento Chamorro
e_pimiento at yahoo.com
________________________________
From: Bulent Arikan <bulent.arikan at gmail.com>
To: grass-user at lists.osgeo.org
Sent: Mon, March 21, 2011 3:03:35 AM
Subject: [GRASS-user] interpolating images with coastal areas
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.
Thanks!
--
BÜLENT
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