Applying same color gradient for three SpatRaster maps with terra::plot in R

Question

I have a SpatRaster created with the terra package in R, and I have two groupings of points within the larger SpatRaster, which I then separate into groups to observe the groupings with more detail. I use terra::plot to plot the larger SpatRaster and the individual groups, but I want to keep the gradient scale the same for all of the plots. The issue is that the range of values for each of the plots differs, and I haven't been able to figure out how to set the lower and upper limits for the color gradient of each terra::plot to be the same so the colors are consistent.

The ggplot2 package did not work for this data because it is SpatRaster data, thus scale_color_gradient does not work, I have tried a combination of the col argument in terra::plot, such as

plot(DTM_50570, main = "DTM", col = data.frame(from = 0, to = 2000, (terra.pal = terrain.colors(255))))

plot(DTM_50570, main = "DTM", col = data.frame(from = c(0, 1000), to = c(1000, 2000), col = terrain.colors(255)))

plot(DTM_50570, main = "DTM", col = data.frame(from = c(0:10:2550), to = c(0:10:2550), col = terrain.colors(255)))

to no avail.

The data that I am using is in this link: https://tinitaly.pi.ingv.it/Download_Area1_1.html, section W50570.

Here is the code I use for plotting and separating the groups:

library(terra)

DTM_50570_32632 <- rast(paste0("Downloads/w50570_s10/w50570_s10/w50570_s10.tif"))
DTM_50570 <- project(x = DTM_50570_32632, "EPSG:4326")

DTM_longitude <- c(11.80111, 11.80222, 11.80333, 11.95111, 11.95222, 11.95333)
DTM_latitude <-c(45.98333, 45.98777, 45.98555, 45.94111, 45.94888, 45.94333)

group_1_extent <- ext(11.80, 11.81, 45.98, 45.99)
DTM_group_1 <- crop(DTM_50570, group_1_extent)

group_2_extent <- ext(11.95, 11.96, 45.94, 45.95)
DTM_group_2 <- crop(DTM_50570, group_2_extent)

DTM_longitude_group_1 <- c(11.80111, 11.80222, 11.80333)
DTM_latitude_group_1 <-c(45.98333, 45.98777, 45.98555)

DTM_longitude_group_2 <- c(11.95111, 11.95222, 11.95333)
DTM_latitude_group_2 <-c(45.94111, 45.94888, 45.94333)

par(mfrow = c(1, 3))
plot(DTM_50570, main = "DTM")
points(DTM_longitude, DTM_latitude, pch = 20)

plot(DTM_group_1, main = "DTM group 1")
points(DTM_longitude_group_1, DTM_latitude_group_1, pch = 20)

plot(DTM_group_2, main = "DTM group 2")
points(DTM_longitude_group_2, DTM_latitude_group_2, pch = 20)

And the resulting plots (that all have different color gradient scales)

It may be that this can be resolved by looking at ?terra::plot range argument, as the colors above are the same, but given the slices of DTM1, DTM2, neither of which have the DTM 1500+ value peak...Well, what I would try as first measure, as overall it seems you want same numbers on each legend. — Chris
– Chris, Commented Apr 15 at 13:29

Robert Hijmans · Accepted Answer · 2025-04-15 14:32:34Z

4

You can use argument "range". If the rasters have the same geometry, you can also use panel instead of plot.

library(terra)
f <- system.file("ex/elev.tif", package="terra")
r <- rast(f)
x <- c(r/2, r, r*2)
names(x) <- c("A", "B", "C")

plot(x, range=c(70, 1100))
# or plot(x, range=range(minmax(x)))

panel(x, nr=1)

answered Apr 15 at 14:32

Robert Hijmans

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