Dear fellow Remote Senseis,
Here is a code chunk that will help you speed up the processing time when you want to extract raster values at specific locations.
It uses the a package called snowfall which allows parallel processing.
As usual, please find here under a dummy example. As there is only 3 bands it the stack, you may not see the positive effect of parallel computing…try with a 100-layer stack and you’ll see.
install.packages("snowfall") library(snowfall) library(raster) ncpus <- 3 r <- (stack(system.file("external/rlogo.grd", package="raster"))) inSlist <- unstack(r) # convert to list of single raster layers rId <- subset(r,1) idPix <- which(rId>200) sfInit(parallel=TRUE,cpus=ncpus) sfLibrary(raster) sfLibrary(rgdal) a <- sfSapply(inSlist,extract,y=idPix) sfStop()