Hi Frank, Not sure this will help, as I am slightly unsure what you are attempting, but you may be able to apply what I did to create a DEM from tiles.
I interpolated my 70 1km tiles with v.surf.rst by interpolating a 1050x1050 cell area (1.05kmsq). I cropped with g.region and r.mapcalc to 1020X1020 (incase of any artefacts - trees are bad for that), and then patched (r.patch) them all together. The patching should average out any differences. I then cropped out each 1km tile (1000x1000). This was done so that the 1km tiles could be combined for specific areas by different people (e.g. only a 4kmsq area for academic 'a' or a 6kmsq area 2km away for academic 'b'). Anyway, from what I understand of your scenario, a hole in a DEM to insert another DEM, create at least a 20 cell overlap for both datasets and r.patch. Hope this helps John On Thursday 25 February 2010 08:45:37 Frank Broniewski wrote: > Hello, > > I am trying to create a high resolution dem from contour lines Until now > all my tries where not successful. At first I tried r.surf.contour, but > since my interpolation region is not rectangular and the contours are not > evenly distributed (rough terrain), the result was unfortunately not > usable ( but it took around 7 days to compute, that alone was already > impressive ;) ) > > My contour map is a combinatin of a national contour line map (5m vert. > resolution) and contours from SRTM with 20m vert. resolution. I created a > "hole" in the srtm contours for the national contour map and patched both > together to avoid large gaps with no height values (mostly for > r.surf.contour) > > My region is 17.000 x 13.000 cells wide (5m horiz. resolution). So my > current approach is to use small regions (2000 x 2000) to calculate small > subsets of the dem. Because of the algo used by v.surf.rst to create the > dem the neighboring tiles do have different height values calculated at > the borders. So it was not possible to just create the tiles and patch > them together. > > My next approach used an overlapping of 20 cells for each tile and a moving > window average to calculate the mean of the overlapping tiles. The result > was quite good, but the moving window approach resulted in null values > where one tile ended and the other started (similar to the slope and > aspect maps, where there is a 1 cell null border around the map in > comparison to the input dem). > Unfortunately I was not able to remove the null values satisfactorily. > r.fillnulls fails because of the large region, and r.resamp.rst does the > job not very well. The stripes are still visible, though filled with > values. When calculating a derivate from the dem, like aspect, the errors > from filling null values are quite obvious. > > So to make my long text short: Is there a technique to combine two or more > raster dem with (or without overlapping) with good transition/intersection > (don't know the correct word) between two tiles? > If necessary I can illustrate my efforts by creating a web page or similar > ... > > Many thanks for tipps > > Frank > > Frank Broniewski > > Metrico s.àr.l. ( http://www.metrico.lu ) > 36, rue des Romains > L-5433 Niederdonven > Luxembourg > > Fon: +352 26 74 94 28 > Fax: +352 26 74 94 99 > > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
