We have a 1-meter LIDAR DEM from a city.
A small subset can be downloaded from this link:
This screenshot shows raw DEM with gray palette (darker belts are streets, and greyish and whitish rectangles are blocks):
This correspond to a place in Santo Domingo city, which can be seen in this Google screenshot:
On average, blocks are "uplifted" ca. 2 meters from streets, which is not true. We want to have a clean DEM to generate stream network and topographic wetness index (TWI). With the DEM supplied (we don't have the original bands from laser scanner), the hydrgraphic network seemed to follow a rectangular layout, and TWI resulted in blocks pattern. These pictures show the results:
This is the stream network result, generated with
And this is TWI result, generated with
We tried some procedures to solve this inaccuracy without success:
1) Denoising tool. We applied
r.denoise tool in
Grass GIS, but got some problems with the module installation. We ran it again with a shell in Windows, and received an insufficient memory message.
2) Filters. We ran different types of filters (low-pass, median, mean, etc.), with different windows sizes, and trying to put weight in the direction of the streets (
3) Geostatistics. We generated points cloud strictly over streets (tried 1000 and 2000 points), generated a variogram model and then ran an ordinary krigging to fill blocks. Variogram modelling, and ordinary krigging, was done in
R, using different packages. We got a linear variogram, so we wouldn't rely on kriging results.
4) Other tools. Installed
ALDPAT tool, but couldn't get it to work because the program couldn't read the DEM.
In all cases, results in terms of the drainage network wasn't good, because we couldn't avoid the rectangular stream network; also, TWI still resulted in a blocks pattern.
In particular, with OK interpolated result, we got a point-like pattern DEM that affected the network result. However, the effect of the blocks pattern was diminished.
Also, we took a look at this question and answers...
...which redirected us to
Whitebox Geospatial Analysis Tools, but couldn't convert our DEM to
LAS format. Also, we were not sure about the effectiveness of
Bare-Earth DEM tool for us, because it's designed for removing semi-transparent objects, not blocks incorrectly "uplifted", which is our case.
We still want to generate a high quality DEM to make our hydrographic analysis, but don't know what else can we try.