[GRASS-user] interpolating with a covariate - v.vol.rst

[Dylan Beaudette]

On Wednesday 07 January 2009, Helena Mitasova wrote:
> On Jan 7, 2009, at 11:19 AM, Dylan Beaudette wrote:
> > On Tue, Jan 6, 2009 at 2:33 PM, Markus Neteler <neteler at osgeo.org>
> >
> > wrote:
> >> Dylan,
> >>
> >> On Tue, Jan 6, 2009 at 10:01 PM, Dylan Beaudette
> >>
> >> <debeaudette at ucdavis.edu> wrote:
> >>> Hi,
> >>>
> >>> For some crazy reason I was under the impression that it is
> >>> possible to do
> >>> interpolation with a covariate with v.vol.rst. Are there any
> >>> examples on how
> >>> to parameterize this module, when a 2D surface is requested,
> >>> rather than a 3D
> >>> volume. I noticed the 'cellinp' argument for a cross-section, but
> >>> this is not
> >>> quite what I am after. I am looking to do something very similar to
> >>> interpolation of rainfall data, taking into account the
> >>> orographic effect of
> >>> terrain.
> >>
> >> This was my main business (say, of our cluster) over the last
> >> months :)
> >> You can do that. I am using the elevation model as auxiliary
> >> variable:
> >>
> >> # something like this:
> >> v.vol.rst in=vectpoints cellinp=dem wcolumn=pointval cellout=rst2d
> >>
> >> cellout delivers the 2D map, extracted from the volume along the
> >> dem map.
> >>
> >> Hope this helps
> >> Markus
> >
> > Thanks Markus. One more question: have you found a good compromise in
> > the 3D region settings- i.e. some ratio of horizontal:vertical
> > resolution that gives good results and doesn't take too long to
> > compute?
>
> you need to set your vertical resolution based on the spatial
> variability you want to capture
> and then don't forget to use appropriate zmult that will stretch the
> vertical distances so that
> they are about the same magnitude as horizontal distances (e.g. if
> your horizontal res. is 10m
> and vertical is 0.1m you need zmult around 100, if you want
> anisotropic effects it may be less -
> see more on how to find the parameters here:
> http://skagit.meas.ncsu.edu/~helena/gmslab/papers/
> TGIS2002_Hofierka_et_al.pdf
>
> I hope this helps, Helena
>
> > Cheers,
> >
> > Dylan

Thanks for the tips Helena. I'll check on that paper, and report back with the 
results.

Dylan

-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341