Erik Hofman wrote: > Jon Berndt wrote: > > > Well, to rotate the aircraft realistically the refference point should > > > be known by the 3D modellers, but that aside. > > > > The rigid body rotates about the CG, not the aero ref. pt. > > Even when in motion? > It seems to me there would otherwise be no need for a refference point.
That's exactly the point. The reference point is a completely arbitrary choice; it could be 4 light years away (well, with infinite precision floating point) and the math would still work just fine. The FDMs do the dynamics for you; if you draw the aircraft where they tell you it is, then you will always be drawing physically correct rotations. It is true that there is an *illusion* that happens when you "look at" a point far from the aircraft's c.g. which makes the airplane look like it is not rotating correctly. But this is an illusion; what is really happening is that the *viewpoint* is moving. The aircraft motion is correct in all cases. The fix for this issue is either to pick an origin near the c.g. (hard to enforce between FDM(s) and 3D model) or to have the view code explicitly "look at" the c.g. point instead of the origin (my preference, although it does complicate things a little). Andy -- Andrew J. Ross NextBus Information Systems Senior Software Engineer Emeryville, CA [EMAIL PROTECTED] http://www.nextbus.com "Men go crazy in conflagrations. They only get better one by one." - Sting (misquoted) _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
