[GRASS-user] Some questions about DEMs

[David Townshend]

Hi

I have a couple of questions about DEMs, and how they work in GRASS. My
application is hydrological and hydraulic analysis, and at the moment I'm
investigating using r.sim.water to generate floodlines.

Usually, for this sort of analysis, I would have 5m contours for the
catchment and a detailed survey (i.e. spot heights, sometimes with
triangles) for sections of river. So my first question is, what is the best
way to generate a DEM from this information? I know that I can use
r.surf.contour to create a DEM from the contours, and I'd assume that
something like v.surf.rst would be best for the points, but I need a single
DEM for the analysis.

The second problem is that I don't need a highly detailed DEM for the
catchment, I only need detail along the watercourses - i.e. where I have the
detailed survey. If I create two DEMs at different resolutions, can I patch
them without losing detail?

My third question is about creating a mask. If I'm working along the coast,
or if I'm creating a detailed DEM along the watercourse, I only want raster
data where there is base data (i.e. contours or points). Is there a way to
quickly generate a mask for this?

Regards
David
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