Dear R-sig-geo users, I have a question about extracting information from a raster file after I read it in using rgdal package, and I would be infinitely grateful if someone could help me. The summary of raster file looks like this:
#summary of raster file > summary(xxx) Object of class SpatialGridDataFrame Coordinates: min max x -180 180 y -90 90 Is projected: FALSE proj4string : [+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0] Number of points: 2 Grid attributes: cellcentre.offset cellsize cells.dim x -179.10 1.8 200 y -89.55 0.9 200 Data attributes: Min. 1st Qu. Median Mean 3rd Qu. Max. NA's 0.000 0.000 0.000 47.010 3.264 13540.000 26563.000 I would like to write a code that extracts the value of associated cell given a specific location in latitude and longitude. I've noticed that [EMAIL PROTECTED] contains the values as 40000 x 1 matrix. I've wrote the following code assuming that the values are stored as in C programing (column wise seperation): #initiate values [EMAIL PROTECTED]@cellsize[1] [EMAIL PROTECTED]@cellsize[2] [EMAIL PROTECTED]@cellcentre.offset[1] [EMAIL PROTECTED]@cellcentre.offset[2] [EMAIL PROTECTED]@cells.dim[1] [EMAIL PROTECTED]@cells.dim[2] #given coordinate x=26 y=45 #find the index index=floor((x-x_start)/x_inc)*y_dim + floor( (y-y_start)/y_inc ) [EMAIL PROTECTED],1] The result does not seem to match what I should get. Could anybody explain to me how the data is stored in SpatialGridDataFrame? Your help would be much much appreciated. Thank you and have a good night Harry _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo