Mathias Fröhlich:

Mathias Fröhlich:

I have prepared a patch that:
- Introduces a FGTileMgr::scenery_available method which asks the tilemanager
  if scenery for a given range around a lat/lon pair is already loaded and make
  use of that method at some -9999 meter checks.
- Introduces a FGScenery::get_elevation_m method which queries the altitude at
  a given position. In constrast to the groundcache functions this is the best
  choice if you ask for one *single* altitude value. Make use of that thing in
  AI/ATC classes and for the current views ground level. At the current views
  part the groundcache is reused if possible.
- The computation of the 'current groundlevel' is no longer done on the
  tilemanagers update since the required functions are now better seperated.

Alltogether it eliminates somehow redundant terrain level computations which
are now superseeded by that more finegrained functions and the existence of
the groundcache. Additionally it introduces an api to commonly required
functions which was very complex to do prevously.