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I downloaded a 'Google Map' terrain map using dismo::gmap. The raster comes with a Mercator projection. I tried to re-project it to UTM but in doing so, all the colors are lost and the raster is not displayed the same way (add scale + coordinates). Could you explain me how to retain the original colors ?

library(dismo)
library(raster)

area  <- extent(678815, 709272, 5004393, 5028388)
proj4 <- "+proj=utm +zone=17 +datum=NAD83 +units=m +no_defs +ellps=GRS80 +towgs84=0,0,0"

r <- raster()
extent(r) <- area
proj4string(r) <- proj4

gm  <- gmap(x = r, type = "terrain", scale = 1)
gm2 <- projectRaster(gm, crs = proj4)


plot(gm)
plot(gm2)

the two output

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1 Answer 1

7

I finally found the way with the option rgb = TRUE and the function plotRGB. It makes a lot of sense once you have the anwser.

library(dismo)
library(raster)

area  <- extent(678815, 709272, 5004393, 5028388)
proj4 <- "+proj=utm +zone=17 +datum=NAD83 +units=m +no_defs +ellps=GRS80 +towgs84=0,0,0"

r <- raster()
extent(r) <- area
proj4string(r) <- proj4

gm  <- gmap(x = r, type = "terrain", scale = 1, rgb = TRUE)
gm2 <- projectRaster(gm, crs = proj4)


plotRGB(gm)
plotRGB(gm2)
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  • 1
    (It's primarily because the default return is a palette image, that can be unpicked as well by applying the raster values as an index into the colour table. Here's an example I've had, I use it for rgl texture mapping gist.github.com/mdsumner/7af4606fcbec6e110233b280974aba8f) Didn't know about the rgb argument, thanks!
    – mdsumner
    Commented Sep 10, 2017 at 10:24
  • @mdsumner you should post as an answer with a bit more explanation :)
    – GISHuman
    Commented Sep 10, 2017 at 18:50

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