How to load Georeferenced Scanned Maps in R

Question

I have a geo-referenced scanned Map in GeoTiff format, which I would like to load into R. My intention is to plot some vector data (points and polygons) over this map using maptools package.

Is there any way to do this in R?

I have tried the raster and rgdal packages, however they give a gridded raster file, rather than the original image. I would like to load the map as an image itself and not a gridded raster file to plot the vector data.

Answer 1

Assuming a 3-band RGB image:

With rgdal see ?SGDF2PCT, or with raster see ?plotRGB - both require a 3-band gridded data set, the raster pathway is simplest.

For example, note that we use brick to ensure multiple-bands are read:

library(raster)
x <- brick('somefile.tif')
plotRGB(x)

And here's a concrete example from the manual:

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

Now you can overplot other data, but note that there is no auto-reprojection in this process, the vector data need to share the coordinate system of the first plot to make sense:

plot(vecdata, add = TRUE)

Any more details really needs some more information from you about your data. There are fairly simple methods to plot palette images as well.