Re: [Flightgear-devel] JSBSIm and altitude-agl-ft

[Renk T. <tho...@jy...>]

> Was this issue caused by the JSBsim ground-handling change or something  
> else? I.e does it exist in 3.0 or only in Git versions?

I'm fairly sure it's not caused by the ground interaction code, but ground interactions would be switched to active if AGL goes close to zero - so then it starts computing _as if_ the plane would be on the ground. I could fly straight through the zone, but I couldn't turn (I suspect) because then one wing came low, and that triggered something which let the wing get stuck.

I suspect without crash detection code and ground interactions all that would happen to a JSBSim plane flying through such a zone is a weird radar altimeter reading (if it's equipped with one). But both crash detection and ground interactions would trigger once the AGL altitude is close to zero.

My guess is that there's something odd in the scenery mesh, giving no terrain level back to the sim, the agl computation defaults to zero if it can't know the value, and zero is problematic for the other systems mentioned above. 

The big question is why YaSim doesn't run into the same problems - I understand it may not default to zero if it can't get terrain, but it seems to be doing just fine with a correct reading. So it's not just the scenery having a discontinuity, there must be something specific for JSBSim.

My two cents...

* Thorsten