Package for automatic interpolation
Hi Thomas, The automatic fitting procedure checks a range of possible variogram models, including Spherical, Exponential, Gaussian and Matern models. Each of these models could lead to a singular model fit. The fitting function in gstat (fit.variogram) says the following on singular model fits: """On singular model fits: If your variogram turns out to be a flat, horizontal or sloping line, then fitting a three parameter model such as the exponential or spherical with nugget is a bit heavy: there's an infinite number of possible combinations of sill and range (both very large) to fit to a sloping line. In this case, the returned, singular model may still be useful: just try and plot it. Gstat converges when the parameter values stabilize, and this may not be the case. Another case of singular model fits happens when a model that reaches the sill (such as the spherical) is fit with a nugget, and the range parameter starts, or converges to a value smaller than the distance of the second sample variogram estimate. In this case, again, an infinite number of possibilities occur essentially for fitting a line through a single (first sample variogram) point. In both cases, fixing one or more of the variogram model parameters may help you out. """' regards, Paul Thomas Adams schreef:
Paul, This is outstanding; thank you very much! BTW, I noticed that when I run your example that I get: Warning: singular model in variogram fit ?actually, 2 such warnings with the OK example, and 1 with the UK example. Are you seeing these too? Otherwise, the results look fine? Thanks again for your contribution! Regards, Tom Paul Hiemstra wrote:
Dear r-sig-geo, In the course of my PhD I have written a R package that performs automatic interpolation (kriging) and might be interesting for other people. I work on real-time automatic interpolation of radioactivity levels. It depends heavily on the gstat pacakge written by Edzer (Pebesma, he is my supervisor). If people are interested in this package, it can be downloaded from http://intamap.geo.uu.nl/~paul/Downloads.html. If you have any comments, complaints or suggestions please do not hesitate to e-mail me. Some sample code: library(automap) data(meuse) coordinates(meuse) = ~x+y data(meuse.grid) gridded(meuse.grid) = ~x+y kr.ok = autoKrige(log(zinc)~1, meuse, meuse.grid) plot(kr.ok) kr.uk = autoKrige(log(zinc)~sqrt(dist), meuse, meuse.grid) plot(kr.uk) cheers, Paul
Drs. Paul Hiemstra Department of Physical Geography Faculty of Geosciences University of Utrecht Heidelberglaan 2 P.O. Box 80.115 3508 TC Utrecht Phone: +31302535773 Fax: +31302531145 http://intamap.geo.uu.nl/~paul