Stefan, your data are definitely not on a grid, so either you transform them back to the grid on which they were, or alternatively you could interpolate them to a new grid, e.g. by
library(sp) link <- "http://z107.de/uni/example16092010.RData"; load(url(link)) coordinates(data) <- c("lon","lat") diff(sort(unique(coordinates(data)[,2]))) diff(sort(unique(coordinates(data)[,2]))) bb = bbox(data) gt = GridTopology(c(bb[1,1],bb[2,1]), c(.18,.18), round(c(diff(bb[1,]), diff(bb[2,]))/.18) + 1) plot(data) plot(SpatialGrid(gt),col='red',add=T) sp = SpatialGrid(gt) fullgrid(sp)=F spx = SpatialPixelsDataFrame(sp, data.frame(x = rep(NA, 44*16))) library(gstat) #proj4string(data)="+proj=longlat" #proj4string(spx)="+proj=longlat" sp2 = idw(Therm.Eignung~1,data,spx) image(sp2,axes=T) spplot(sp2[1], col.regions=bpy.colors()) On 09/16/2010 08:31 PM, Stefan Muthers wrote: > Hello, > > this is probably a beginners question, but I found no solution on the > web. > > If am using data from a climate model with the cell positions given in > geographic coordinates. Unfortunatly the distance between the cells is > uneven (due to runding errors and maybe the projection) and the > "gridded" command fails to determine the correct cell size. > > > Consider the following example: > > > library(fields) > library(sp) > > link <- "http://z107.de/uni/example16092010.RData"; > load(url(link)) > > coordinates(data) <- c("lon","lat") > gridded(data) <- TRUE > # Warnmeldungen: > #1: In points2grid(points, tolerance, round, fuzz.tol) : > # grid has empty column/rows in dimension 1 > #2: In points2grid(points, tolerance, round, fuzz.tol) : > # grid has empty column/rows in dimension 2 > > data_sp <- as(data, "SpatialGridDataFrame") > g_plot <- as.image.SpatialGridDataFrame(data_sp["Therm.Eignung"]) > image.plot(g_plot) > > > > The resulting map contains only small stripes and much empty space. > summary(data) reveals, that the cellsize if much to small (cell should > be quadratic with a cellsize of ~ .16) and to many cells were found in > the y-direction. > > When I replace the lat and lon values with simple x and y coordinates, > everything works fine, but then it is not possible to overlay a shape > file, that displays the country borders. > > Any ideas, why the cellsize-estimation is so different from the real > value and what I can do, to create a raster map with this data? > > > thank you and best regards, > > stefan > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@stat.math.ethz.ch > https://stat.ethz.ch/mailman/listinfo/r-sig-geo -- Edzer Pebesma Institute for Geoinformatics (ifgi), University of Münster Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251 8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de http://www.52north.org/geostatistics e.pebe...@wwu.de _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
