[GRASS-user] Re: QGIS GRASS plugin shadedrelief issue

Hamish hamish_b at yahoo.com
Sun Sep 19 16:26:48 EDT 2010

Sab wrote:
> There is a native QGIS plugins:
> http://spatialserver.net/pyqgis_1.0/contributed/shadedrelief.zip
> To activate it in QGIS:
> Fetch Plugins, a new window will pop up:
> Click on Repositories tab
> Add 3rd Party repository
> Click on Plugins
> Install DEM relief Shader
> You should be able to create relief shade as TIFF format
> from your dem.

note that (gdaldem/hillshade) is just based on repackaged GRASS
algorithms, so a problem in one might also be seen in the other.

-> see  http://grass.osgeo.org/wiki/Contour_lines_to_DEM

r.surf.contour is the right tool to use here, but the user should
pull off peak heights from the original topo map scan so that
above the top contour is not a flat mesa. also the trick shown
on that page should be used to multiply by a large number before
running it, and then divide afterwards, to avoid the terracing
effect which is caused by r.surf.contour only working with
integer heights so far.

I wonder if the black-spots are a color table problem? what does
r.univar say about the shaded relief map?

before running v.surf.rst (or any raster op.) be sure to run
g.region to set up the computational region as desired. maybe
your original topo map scan gives good values to match, although
you'll probably want the resolution to be a nice round number
(use the g.region res=.. -a flag).



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