Unexpected behavior of raster "mask" function
Alex, Thanks for the clear example. I had not considered that case. I have added an argument 'updateNA' to the mask function (version 2.2-43) such that you can do: masked_image <- mask(img, msk, updatevalue=2, updateNA=TRUE) That is, if updateNA is TRUE, NA cells outside the mask are also updated. Robert On Fri, Jul 18, 2014 at 11:18 AM, Alex Zvoleff
<azvoleff at conservation.org> wrote:
I am using the mask function in the raster package (2.2-38) to mask out areas within an image that are outside an area of interest (AOI). There are NAs within this AOI that are meaningful - after masking the image I am using freq to tabulate these NAs along with the other values in my AOI. For this reason, I am using the "updatevalue" option in the mask function to recode all areas outside of my AOI to a value (say 99) so that I can ignore these areas in subsequent analysis, without having ignored areas share a value (NA) with areas inside my AOI. However, the mask function does not operate as I expected - areas in the image that should be masked but that are NA prior to masking are not set to "updatevalue". Is there an way to tell the mask function to recode all areas (regardless of their initial value) to updatevalue? The below example shows my problem: library(raster) # Setup an image with two NA values. Make one NA value inside # the AOI, and make the other outside the AOI img <- matrix(1, nrow=5, ncol=5) img[3, 2] <- NA # Inside AOI img[1, 2] <- NA # Outside AOI img <- raster(img) plot(img) # Setup a mask where only the 3x3 region in the center of img is retained msk <- matrix(1, nrow=5, ncol=5) msk[1,] <- NA msk[5,] <- NA msk[,1] <- NA msk[,5] <- NA msk <- raster(msk) plot(msk) # Apply mask masked_image <- mask(img, msk, updatevalue=2) # Notice that cell (1, 2) of masked_image is NA, instead of the updatevalue (2). # This cell was not affected by the mask because it was NA prior to calling mask. # Is there a way to tell the mask function to set all masked areas to updatevalue, # regardless of whether a cell is NA prior to masking? plot(masked_image) Thanks, Alex -- Alex Zvoleff Postdoctoral Associate Tropical Ecology Assessment and Monitoring (TEAM) Network Conservation International 2011 Crystal Dr. Suite 500, Arlington, Virginia 22202, USA Tel: +1-703-341-2749, Fax: +1-703-979-0953, Skype: azvoleff http://www.teamnetwork.org | http://www.conservation.org [[alternative HTML version deleted]]
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