Dear Else, I've read your message twice, but I am still not sure what exactly you want to run: (1) which prediction technique, (2) for which purpose (validation only?).
Using the krige.cv method, you can also run the cross validation for inverse distance interpolation (note: you only need to omit the variogram): > idw.zn.cv <- krige.cv(zinc~1, meuse, nfold=2) [inverse distance weighted interpolation] ... This is all explained in Edzer's paper on gstat: Pebesma, E.J. 2004. Multivariable geostatistics in S: The gstat package. Computers and Geosciences 30: 683–91. http://dx.doi.org/10.1016/j.cageo.2004.03.012 see also pages 222-226 in Bivand et al. (2008) code available at: http://www.asdar-book.org/book/geos_mod.R here are some similar simple examples: http://spatial-analyst.net/wiki/index.php?title=Spatial_prediction_of_soil_moisture HTH Tom Hengl -----Original Message----- From: r-sig-geo-boun...@stat.math.ethz.ch [mailto:r-sig-geo-boun...@stat.math.ethz.ch] On Behalf Of Els Verfaillie Sent: Tuesday, March 24, 2009 3:00 PM To: r-sig-geo@stat.math.ethz.ch Subject: [R-sig-Geo] residuals by subtracting point values from grid values Hi list, I've splitted my dataset (e.g. the meuse dataset) into random 2 parts (2/3 for prediction and 1/3 for validation). I've done an interpolation (e.g. IDW, but I also want to do it with different kriging techniques) based on the prediction dataset. Now I want to subtract the "zinc" values from the validation dataset (i.e. a SpatialPointsDataFrame with 52 points) from the "var1.pred" values from the interpolation (i.e. a SpatialPointsDataFrame with 3103 points) to obtain the residuals. This of course only on the location of the 52 points from the validation dataset. Then I want to calculate validation indices. This is my code: #Validation and prediction dataset permid <- sample(155) idportion <- 1:round(2*155/3) meuse.pred <- meuse[permid[idportion], ] meuse.val <- meuse[permid[-idportion], ] #idw based on meuse.pred idw.pred.zn <- idw(zinc ~ 1, meuse.pred, meuse.grid) I know that I could use the "krige.cv" to do an n-fold cross-validation, but I would like to do it based on the above method. Any suggestions? Thanks a lot! Els ______________________________________________ Dr. Els Verfaillie Carto-GIS cluster Ghent University (UGent) - Department of Geography Krijgslaan 281 - S8 B- 9000 Gent Belgium ______________________________________________ [[alternative HTML version deleted]] _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo