bwtr think of GeoControl as a helper tool for Carrara you dont need it but it is a good companion tool, Carrara is very powerful and has a great landscape editor GeoControl works a little different.

This program lets me generate landscapes and then tweek it to what I need without having to spend a lot of time learning a new system. It's easy or complex depends on how you want to use the program.

I havn't used Ground Control but I dont think it has a landscape editor, I could be wrong but I thought it was a converter.