XGlobe currently has all the features I wanted. That doesn't mean 
it couldn't be improved:

- orbit as positions specifier as in xearth
- "don't show markers on dark side"-option
- rewrite the ugly map-interpolation code
- XGlobe uses quite a lot of memory: Supporting 8-bit maps directly
  would help
- use autoconf and automake for an easier setup process
- use qImageIO library (should work, but I didn't test it yet)

- get cloud data from the internet and overlay it onto the globe
  (this would be an absolutely cool feature)
