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I have a problem with my DEM again. I decided to use ASTER GDEM2 (for different reasons). ASTER GDEM2 have its problems, I know, and I dont want to discuss that again. I have to use it, because SRTM (USGS, CSI; Viewfinder) is not usable for my purpose.

So, there are 2 bad areas in my ASTER DEM: enter image description here

These areas a nearly okay in CSI so I could fill these errors of the ASTER GDEM2 with it. But I guess, the result wont be as good as I want to (the mountain in fact is 500m from ground! SRTM say 350m). I also have a topographic map, a very old one, but the contours seems to be more accurate then SRTM and ASTER.

How can I correct the ASTER GDEM with SRTM or analog contours from my map?


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1 Answer 1

The interpolation modules in GRASS can work with a line vector, such as contour lines, to create a DEM raster. So you could create a DEM raster from your contour lines, then "correct" the ASTER GDEM with this data. The catch will be in matching elevations from the contour-based raster to the ASTER GDEM, to avoid a terrace effect at the edge. The procedure might be:

# Import the contour lines, 
# clipping to include only the area you want to correct, then:  
v.in.ogr dsn=contour.shp out=contour type=line spatial=xmin,ymin,xmax,ymax
# Set the region to match this new vector, 
# and choose resolution suitable for the size of the area
g.region -p vect=contour res=10
# Now interpolate contour-based dem
v.surf.rst in=contour elev=ctour_dem
# Import your ASTER tile and set region to that map
r.in.gdal in=aster.tif out=aster_dem
g.region -p rast=aster_dem
# Finally, patch the two rasters such that 
# pixels from the correct dem replace the aster_dem
# r.patch users the first raster in the list, 
# then fills in null cells from the second
r.patch in=ctour_dem,aster_dem out=correct_dem

That might help

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...trying it this way, thanks so far! –  MAP Jun 24 '12 at 7:51
You must be aware of the vertical differences of the two models, because of 3D different ellipsoids (but these differences do not go over 50 m). –  Niculita Mihai Jan 31 '13 at 12:05
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