[STATSGRASS] krigged dem lost detail
Carlos "Guâno" Grohmann
carlos.grohmann at gmail.com
Wed Mar 22 13:50:33 EST 2006
OK Roger. There are some files at:
http://www.igc.usp.br/pessoais/guano/karst.html
There is a TIFF (and TFW) of the karstic region.
There are 3 region files I've been using, one for the original srtm
resolution, one subset I used to calculate the variogram and one with
the same extents as the first, but with 30m resolution.
And there is a ZIP with all of the above.
Carlos
On 3/17/06, Roger Bivand <Roger.Bivand at nhh.no> wrote:
> On Wed, 15 Mar 2006, Markus Neteler wrote:
>
> > Carlos,
> >
> > I didn't follow this thread in details (although very interesting).
> > There is cross validation for optimizing tension and smoothing,
> > did you make use of that (sorry, if already written...)?
>
> I think that Hamish and Markus are right: both rst and kriging have
> parameters which may lead to this result if set in particular ways. Maybe
> cross validation is a way of comparing their leave-one-out prediction
> performance for (for example) a subscene of the STRM data you've been
> using.
>
> You'd have to try a bit to find out which parameters might be the critical
> ones. I have compared gstat kriging using CV with Tps in the fields
> package, I have a presentation with the gory details (it was actually
> comparing with GeoStatistical Analyst on the Meuse Bank data, gstat with
> the flood frequency factor in R came out best).
>
> Because upgrading 90m data is likely to be something a lot of people want
> to do, it would be worth trying to find out what is going on here. Can you
> post a suitable subscene and its location metadata - say as a geotiff?
>
> Roger
>
>
>
> >
> > I received a script from Jaro to automate the parametrization.
> > Let me know if you need it (maybe it should go into the Wiki,
> > so that you/others could document the procedure)
> >
> > Markus
> >
> > On Wed, Mar 15, 2006 at 07:16:11PM +1300, Hamish wrote:
> > > > I am comparing the results we get when re-interpolating a DEM to a
> > > > higher resolution. I did it with krigging (in R, with gstat) and with
> > > > RST. In the final result it looks like the krigged DEM has lost
> > > > detail, while the RST DEM kept those.
> > > > see it:
> > > > http://www.igc.usp.br/pessoais/guano/tempo/krigging.jpg
> > > > http://www.igc.usp.br/pessoais/guano/tempo/rst.jpg
> > > >
> > > > I don't know why this happens, since they were interpolated wit the
> > > > same resolution, based on the same dataset.
> > >
> > >
> > > be careful you haven't added detail that isn't really there due to
> > > spline artifacts. Perhaps resample known DEM at lower resoution and then
> > > re-interpolate at original resolution to compare which does a better
> > > job recreating the original DEM?
> > >
> > > r.resamp.rst
> > >
> > >
> > >
> > > Hamish
> > >
> > > _______________________________________________
> > > statsgrass mailing list
> > > statsgrass at grass.itc.it
> > > http://grass.itc.it/mailman/listinfo/statsgrass
> >
> >
>
> --
> Roger Bivand
> Economic Geography Section, Department of Economics, Norwegian School of
> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
> e-mail: Roger.Bivand at nhh.no
>
>
--
+-----------------------------------------------------------+
Carlos Henrique Grohmann - Guano
Geologist M.Sc - Doctorate Student at IGc-USP - Brazil
Linux User #89721 - carlos dot grohmann at gmail dot com
+-----------------------------------------------------------+
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