My purpose is to make a graphical representation using the command "persp" of a digital terrain model. I have to start form these points: -a digital terrain model (computed on 25 meters) -the same digital terrain model, this time computed on 5 meters These data are easily available as .txt files on the website. Once I get these files, i turned them into matrices (using the following script: data25<-read.csv('Cortina25.txt') z<-data z<-as.matrix(z) data5<-read.csv('Cortina5.txt') k<-data k<-as.matrix(k) Now the thing I have to do this step: -I need to extract a submatrix from k in such a way that at the end I should get the graph of the dtm 25 with the small portion of the dtm5 superposed on it that corresponds to the submatrix of k. I hope I've been clear. Thank you for your help -- Chiara Odorisio [[alternative HTML version deleted]]