[GRASS-user] interpolating images with coastal areas

[Edgar Pimiento]

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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