On 23/03/2011 17:18, Bulent Arikan wrote:
Dear List, If you're starting with an ASTER DEM (GTiff?) then don't you want to be using r.resamp.rst to interpolate to a higher resolution ?? This module creates, on the way, slope, aspect, curves, etc. Also, one additional point the bears mentioning. If you simply change the resolution to 10m then use r.mapcalc to make a new copy of the original DEM, it will have the newer resolution. This method doesn't do any sophisticated interpolation, just calculates new values for higher res cells by (I think) nearest neighbor. But since you're dealing from the start with the ASTER data, which might have anomalies anyway, maybe this approach might be good enough. It will certainly be *much* faster to run r.mapcalc at higher res than to do an interpolation. Might be worth to cut out a small mountainous region and try both r.mapcalc and r.resamp.rst then compare them... Please post whatever you decide to do in the end. additional maps such as slope, aspect, prof curv, etc. I will try describing my problem below and I will appreciate any suggestions/ideas. Since the original 30m res. image covers a large area, I cropped it into several tiles using 'r.mapcalc'. Each tile has about 12 million cells in 30m res. and 115 million cells in 10m res. and takes an average of 4 hrs to complete one run of v.surf.rst. I sample each tile using 'r.random' at 50%. Then I change the region settings in 'g.region': I align region to resolution and set the resolution to 10m before running v.surf.rst. I ran the module at different tension settings (55., 40., 25. and 10.) while keeping smoothing parameter (.1) and other parameters at default settings. When I add legend to my 10m DEM from the toolbar in Map Display, the elevation range is usually a couple meters above or below the original map. After each run, I set my region resolution back to 30m, and using r.mapcalc, I prepare a "difference" map [ (30m DEM) - (10m DEM) ]. In this map, I get extremely high and low values (i.e., the range in the difference map can be -70 to 183 suggesting to me that there is both over- and undershooting), which seem to be limited to mountain tops and some canyons. When I run 'r.report', I can see that actually these "extreme" values are limited to very few cells (about 3-5% of 12 million cells) and the main variation for 95% of cells is within more reasonable range such as +/- 3 meters. I recently became aware of some accuracy issues related to ASTER DEMs especially in mountainous areas however, I have the same issue for flat parts of this landscape as well. --
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