extracting and manipulating a RasterStack
Hi Sara, The following is slightly different from what you are trying to do, but should give you an area value for cells of a given value, without having to stack your rasters: r <- raster(ncol = 10, nrow = 10) res(r) <- 10 # Giving it a square grid cell, which remakes raster into 18 rows & 36 columns r[] <- 1:ncell(r) plot(r) z <- ((r == 50) | (r == 75)) * 1 # Binary raster plot(z) # The following would give you area in hectares for the selected cells, # assuming that your actual raster is projected in units of meters # (e.g. UTM, Albers) unlike the dummy raster here (sum(getValues(z)) * res(r)[1]^2) / 10000 [1] 0.02 I hope that is somewhat on the mark. Interestingly, I get the following error when I try to use area:
t <- area(r)
# Error in b - a : 'b' is missing Cheers, Lyndon
On Mon, Aug 8, 2011 at 6:07 PM, Sara Maxwell <smaxwell at ucsc.edu> wrote:
I have been struggling with something seemingly straightforward for several days now, and am hoping for some assistance. I have calculated the area for cells within a raster, and now want to extract the area for specific cells and sum the area of those cells together. ?I have tried a number of functions such as stackSelect, but think I have had trouble using the proper syntax in my logical statements. I am new to the raster package, however, so this may be my issue. For example, if I have data that looks like this: require(raster) r <- raster(ncol=10, nrow=10) r[]=1:ncell(r) t <- area(r) s <- stack(r, t) for all values in first layer of s (equivalent to the raster r) with the values 50 and 75, I want to take the corresponding values in the second layer (equivalent to t), create a new raster (call it 'z') where the remaining cells are given a value of 0 (or NA) and finally sum the values of the z. Any suggestions appreciated. Thank you, Sara ? ? ? ?[[alternative HTML version deleted]]
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