given is a raster as well as a SpatialPolygonsDataframe. In order to retrieve the highest value of the raster within the area of a polygon, raster::extract can be used. It works fine.
How to get additionally the coordinates of the extracted highest value of the raster within the area of a polygon?
# create raster
r <- raster(ncol=36, nrow=18)
r[] <- runif(ncell(r))
# create SpatialPolygons from GridTopology
grd <- GridTopology(c(-150, -50), c(40, 40), c(8, 3))
Spol <- as(grd, "SpatialPolygons")
# create SpatialPolygonsDataFrame
centroids <- coordinates(Spol)
x <- centroids[,1]
y <- centroids[,2]
SPDF <- SpatialPolygonsDataFrame(Spol, data=data.frame(x=x, y=y, row.names=row.names(Spol)))
# extract max value of raster for each SpatialPolygon
ext <- raster::extract(r, SPDF, fun=max)
*example code is taken from R-documentation
You can use the cellnumbers=TRUE
argument in extract
, followed by a sapply
to get the cell number:
ext <- raster::extract(r, SPDF, cellnumbers=TRUE)
v <- t(sapply(ext, function(i) i[which.max(i[,2]), ] ))
# cell value
# [1,] 185 0.9303460
# [2,] 188 0.9821190
# [3,] 154 0.9926290
# [4,] 232 0.8907819
# [5,] 234 0.9998510
To get the coordinates:
xyFromCell(r, v[,1])
# x y
# [1,] -135 35
# [2,] -105 35
# [3,] -85 45
# [4,] -25 25
# [5,] -5 25
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