从光栅块中提取特定的单元格值

Question

I have calculated the Wind Speed and Wind Direction from two Raster Bricks.

Now I want to extract the Maximum Wind Speed for each cell. I did that. Now the problem is that I also need the Wind Direction for that specific cell.

my code looks like this:

speed <- brick(speed)
direction <- brick(dir)
maxWindspeed <- max(speed, na.rm = TRUE) # this gives me a raster with the Max Wind Speed Values

Anyone has an idea how to get the specific Wind direction cell for the Max Wind Speed cell in the "maxWindspeed" layer?

Best Regards Max

Answer 1

I don't know if I have understood correctly what you want to do but maybe you can try this:

library(raster)
#simulate data
r <- s <- t <- raster()
r[] <- sample(1:10,ncell(s),replace = T)
s[] <- sample(2:11,ncell(s),replace = T)
t[] <- sample(3:13,ncell(s),replace = T)

speed <- brick(r,s,t)
direction <- brick(r*s,s/t,t-r)
#max values across layers in speed
maxWindspeed <- max(speed, na.rm = TRUE)
plot(maxWindspeed)
plot(direction)
#boolean raster of where maxWindspeed is max
masker <- maxWindspeed==max(maxWindspeed[])
#brick of values in direction where maxWindspeed is max
plot(maxdirection <- mask(direction,masker,maskvalue=0))
#max values across layers in maxdirection
maxdirectioncell <- max(maxdirection,na.rm = T)
plot(maxdirectioncell)

Answer 2

With raster you can use which.max and stackSelect . Using Elia's (slightly modified) example data

library(raster)
r <- s <- t <- raster(ncol=10, nrow=10, crs="+proj=utm +zone=1 +datum=WGS84")
r[] <- sample(1:10,ncell(s),replace = T)
s[] <- sample(2:11,ncell(s),replace = T)
t[] <- sample(3:13,ncell(s),replace = T)
speed <- stack(r,s,t)
direction <- stack(r*s,s/t,t-r)

mxspeed <- which.max(speed)
sdir <- stackSelect(direction, mxspeed)

With terra you can use selectRange

library(terra)
spd <- rast(speed)
dir <- rast(direction)

mxspd <- which.max(spd)
sd <- selectRange(dir, mxspd)