The DEM Earth Geo Reference Tag is used to keep images aligned to DEM Earth Surface.
Images are projected onto the surface, and this tag manages that projection process, so that when you change the DEM Earth location, or zoom level, the material/image scales and moves correctly with DEM Earth in geographic space.
You an use any image with the geo ref tag. it does not have to be something you downloaded. it can link to and use any texture, or shader.
The Tag must be placed on a DEM Earth object. One will be created each time you download a texture via DEM Earth. It has a link to a texture tag and the coordinates of that texture tag are controlled/driven by the georef tag.
The georef tag has 3 modes.
1. World File Transform Factors
These are auto filled if you have a world file which defines the geographic bounds of your image.
2. Image Boundary
You define a box n,s,e,w, which your image fits into.
3. Image Center
You define the center if the image, then its size in geographic meters.
There are a couple of buttons to grab the boundary of from the DEM Earth parent, or transfer the boundary to the DEM Earth parent.
Starting with R4, there is a field for controlling multiple Texture tags, from one georef tag. This is useful for driving shaders that combine multiple materials, so you don't have to duplicate georef tags.
There are also option to fine tune the location.
tips:
if you have a world file and image, you can drag drop it into c4d, and DEM Earth will set everything up for you from that file.
you can use any imagery, from any source. The tag simply controls the projection. you decide what it projects, and where it should project it to.