How to get RGB raster image with UTM coordinates

Question

I have a three layer raster with red, green, and blue channel values in it. I can plot the image with raster::plotRGB, but I need to add axes with UTM coordinates. Coordinates can be added with axes=TRUE, but they are floating in space and look bad. I would like to get the coordinates as they show up in plots created with the raster plot method, or better yet as they appear when using rasterVis::levelplot.

Ultimately, I need to create a raster image with UTM coordinates, a scale bar, and north arrow. This needs to be done using the plotRGB function in the raster package of R, or something with a similar functionality, as I need to assign the colour of each pixel by hand (no colour ramps).

Supply a small example, with reproducible data, showing what you've got so far and what you don't like about it? — Josh O'Brien, Apr 18 '13 at 23:05
Could you provide us with more detail about the origin of your data and the file format? — Paulo E. Cardoso, Apr 19 '13 at 20:48
@klar, [this post](http://gis.stackexchange.com/questions/62740/raster-spplot-legend-how-to-add-a-title-beside-it) may be useful for you. — Paulo E. Cardoso, Feb 26 '14 at 22:42
[reproducible example](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) [reproducible example](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) — shekeine, Dec 13 '15 at 19:26

jbaums · Answer 1 · 2016-01-06T07:07:14.790

This is an ancient post, but it's a good question so I'll give it an answer.

I'll give an example of how this might be done with rasterVis::levelplot, using the 3-channel R logo raster data that comes with raster.

library(rasterVis)
b <- brick(system.file("external/rlogo.grd", package="raster"))

Plotting three-channel RGB rasters with levelplot

Create an empty raster with the same dimensions and extent as the brick.

r <- raster(b)

Calculate the hexadecimal colours corresponding to the values of the RGB channels, and coerce to factor.

cols <- factor(rgb(b[], maxColorValue=255))

Assign these factor values to the raster's cells.

r[] <- cols

Plot with levelplot, extracting the hexadecimal colours from the levels of cols and passing them to col.regions.

levelplot(r, col.regions=as.character(levels(cols)), colorkey=FALSE)

Adding north arrow and scale bar

For the north arrow and the scale bar, we will look to @OscarPerpiñán's docs.

levelplot(r, col.regions=as.character(levels(cols)), colorkey=FALSE) +
  layer(SpatialPolygonsRescale(layout.north.arrow(), offset = c(5, 10), scale = 10)) +
  layer({
    xs <- seq(5, 25, by=5)
    grid.rect(x=xs, y=5,
              width=5, height=2,
              gp=gpar(fill=rep(c('transparent', 'black'), 2)),
              default.units='native')
    grid.text(x=xs-2.5, y=8, seq(0, 400, by=100),
              gp=gpar(cex=0.7),
              default.units='native')
  })

I'll leave it up to you to calculate the true distance (passed to grid.text) associated with the width, in map units, of the rectangles.

How to get RGB raster image with UTM coordinates

1 Answers1

Plotting three-channel RGB rasters with levelplot

Adding north arrow and scale bar