[R-sig-Geo] Aligning an image with a map

[Barry Rowlingson]

On Thu, Jul 5, 2012 at 9:36 AM, Cave, Mark R. <mrca at bgs.ac.uk> wrote:
> I have a jpeg image which I wish to overlay on a map. What is the best approach?
>

 If you know its bounds and the coordinate system of its bounds then
create a world file (.jpgw) and then it should be usable to the gdal
library, and hence read in with the raster package...

FYI:

http://en.wikipedia.org/wiki/World_file

If you don't know the bounds then you need to georeference it -
assigning known points on the image (the summit of a hill, the
junction of a road etc) to true coordinates, and then working out the
transformation.

 Quantum GIS has a handy georeferencing feature where you click on
points on your image and then click on corresponding points on your
Qgis project, so you can load in a background layer (say, from
OpenStreetMap) and then register features in your image to those on
OpenStreetMap. Then once you've added enough references, Qgis will
compute the necessary transformation.

Barry