Hi, I'm happy to say that I think I was able to perform the IDW interpolation. I was able (thanks to Minti) to import the file in asc format I made in qgis to use as the grid (newdata). And it worked. Because I know that there are more people struggeling with IDW, I post hereunder what I did, so maybe I can help them. I'm not sure that this is a good way but it looks like it's working fine for me.
I still have a question. I'm looking for a function (or the package) with which I can extract values out of my IDW output file. I have a file with several sampling points (several coordinates) for which I want to know the precipitation which I interpolated between my rain gauges. I was thinking about the function extract but this one isn't working because: Error in function (classes, fdef, mtable) : unable to find an inherited method for function "extract", for signature "SpatialPixelsDataFrame", "SpatialPointsDataFrame" I think it only works for a raster, but I don't know how to transform my IDW output to a raster... If somebody knows how I can extract the values for my dataframe with coordinates, preferably all at the same time. Is there a default number that most often is used as idp number? I'm still looking which one could be most appropriated. Kind regards, Nerak The script I used now: ###Inverse distance weighted interpolation rm(list = ls(all = TRUE)) library(gstat) library(rgdal) library(raster) library(spatstat) data<-read.table("D:\\... filecoordinatesandprecipiation.txt",header=TRUE) coordinates(data) <- c("x", "y") r2 <- raster("D:\\... IDWrasterfileqgis.asc") r2 <- as(r2, "SpatialPixelsDataFrame") gridded(r2) <- TRUE projection(data) <- "+proj=utm +zone=35 +datum=WGS84" projection(r2) <- "+proj=utm +zone=35 +datum=WGS84" idw.out <- idw(X27_5_2002 ~ 1, data, r2, idp = 2.5) spplot(idw.out, "var1.pred") -- View this message in context: http://r-sig-geo.2731867.n2.nabble.com/performing-IDW-interpolations-tp7580956p7580962.html Sent from the R-sig-geo mailing list archive at Nabble.com. _______________________________________________ R-sig-Geo mailing list R-sig-Geo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo