[GRASS-user] Generating DEM from bare ground LIDAR data: v.surf.idw or v.surf.bspline ?

[Hamish]

Stephen wrote:
> I have a multitude of DEMs to generate at 1m resolution.  Are there
> any references that compare v.surf.idw and v.surf.bspline?

a place to start:
  http://grass.osgeo.org/wiki/LIDAR#Surface_generation

some other options there, e.g. v.surf.rst or r.in.xyz+r.surf.nnbathy.

> Any advice or experience with either of these two modules would be
> helpful. Which one of these modules creates the most accurate
> representation of the surface.

I think it really depends on what you want to do with the DEM. Some methods
are better for hydrologic analysis, others for slope analysis, but fail
at sharp changes like the bottom of cliffs, others will chop off mountain
peaks, etc.

not valid for LIDAR input, but fyi here's a similar look at contour line
to DEM generation:
  http://grass.osgeo.org/wiki/Contour_lines_to_DEM

it would be nice to have something like that for point input as well.
see also v.surf.rst's cross-validation procedure.

FWIW v.surf.bspline was written with LIDAR in mind.

> This will be with NC data- in fact the same 2001 data that is included
> in the new GRASS dataset.  I am working on a project in NC if this
> helps.

You might talk to Doug Newcomb, I believe he's already processed the
entire state.

> Thank you for all of your help, and I will provide any information that
> you may need.  Also, if I use v.surf.bspline is the 1.5*point average
> point spacing still the rule of thumb (the point spacing is found with
> running v.surf.bspline with the -e flag?).

(no idea)

> Thank you so much for all of your help.


regards,
Hamish