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rrasterlevelplotrastervis

Add arrows to levelplot

I would like to add some arrows to a categorical raster plot. Using Base R (on a non-ratified raster) as an example:

r <- raster(nrow=10, ncol=10, crs='+proj=utm +zone=1')
r[] = 1
r[51:100] = 3
r[3:6, 1:5] = 5

plot(r)

arrows(100, 50,
       0, 50, 
       length = 0.1, 
       lwd=2,
       col="red"
)

In levelplot you must first ratify your raster and add the appropriate levels:

r <- raster(nrow=10, ncol=10, crs='+proj=utm +zone=1')
r[] = 1
r[51:100] = 3
r[3:6, 1:5] = 5


r <- ratify(r)
rat <- levels(r)[[1]]
rat$landcover <- c('Pine', 'Oak', 'Meadow')
rat$class <- c('A1', 'B2', 'C3')
levels(r) <- rat

levelplot(r)

How can I add the red arrow (as shown in example 1) to the levelplot() shown in the second block of code?

Thanks.

Solution

  • You can solve it with layer and panel.arrows:

    levelplot(r) + 
   layer(panel.arrows(100, 50, 0, 50, 
                      col = 'white'))