[STATSGRASS] krigged dem lost detail

[Roger Bivand]

On Wed, 22 Mar 2006, Carlos "Guâno" Grohmann wrote:

> 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.
> 

If somebody else would like to join in, please do. Does anyone feel called 
to get the STRM of say spearfish at 30m and 90m and see how close we can 
get to the 30m interpolating from the 90m? That would give us a chance to 
see where things fall apart?

Roger


> 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
> +-----------------------------------------------------------+
> _________________
> "Good morning, doctors. I have taken the liberty of removing Windows
> 95 from my hard drive."
> --The winning entry in a "What were HAL's first words" contest judged
> by 2001: A SPACE ODYSSEY creator Arthur C. Clarke
> 

-- 
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