Mathias Fröhlich:

Mathias Fröhlich:

I have some small updates to the ground cache.

- Remove the usage of dynamic_cast where it is known that the result will be
  non null.
- Renormalize the surface normal in double precision.
- Place the groundcaches center at the point it was requested not at the
  scenery center. This fixes the problems with JSBSim's trimming together with
  the ground cache. Now I am ready to commit JSBSim's ground cache usage.