[GRASS-user] High resolution dem

[Frank Broniewski]

Hi,

> Hamish:Feb 28, 2010; 03:15am Re: High resolution dem
> I am curious to know what the problem with r.surf.contour was. Usually
> it does a great job as long as you take a moment to work around the
> integer and NULL/0 issues.

Sorry that I quitted this discussion so silently, but I had to drop this 
and could not persue the issue further. Sometimes I really could use a 
48h day :-)
Of course my problems are still present. To take the thread up again, I 
want to answer to Hamish's question about my problems with 
r.surf.contour first:

DEM interpolation seems to work nice, but when you start deriving maps, 
especially the aspect map looks simply not right ;-)
I've uploaded some example images on our server, so that you can see 
what I mean:

http://www.gis-hosting.lu/static/img/grass/contours5m.png
http://www.gis-hosting.lu/static/img/grass/dtm5m.png
http://www.gis-hosting.lu/static/img/grass/dtm3d.png
http://www.gis-hosting.lu/static/img/grass/expo5m.png

The data source is a shape file with contour lines with 5 meters 
interval. Conversion to raster went well and the pixel values match the 
height values for the contours. Before using the raster map, I 
multiplied the map with 100000, just like it is mentioned in the wiki. 
Interpolation took approx. 5 minutes. The region is 10,000m * 10,000m 
wide and has a 5m resolution. Before deriving the aspect map, I divided 
the elevation map by 100000 to gain real height values again ...

Now I wonder what could cause the gaps in the aspect map - since the 
terrain model itself looks OK to me ...

Many thanks

Frank

-- 
Frank BRONIEWSKI

METRICO s.à r.l.
géomètres
technologies d'information géographique
rue des Romains 36
L-5433 NIEDERDONVEN

tél.: +352 26 74 94 - 28
fax.: +352 26 74 94 99
http://www.metrico.lu