Alan wrote: > Note this fact. If you have the CG point as the reference, then scale > matters very little to the motions of flying. Only the point reference makes > the models match reasonably well. You still need a distance measurement to know > the scale and work out CG shifts, where the nose, wheel, and tail really are, > etc though. Even the control forces off. But the motion point is not, for both > rotation and translation.
<sigh> The simulation world seldom works out like a hand in glove. There are always tradeoffs. We designed the current system to handle these *facts*: 1) The 3D modeler will not know or care about where the CG is. We often may inherit a visual model from another project. 2) The FDM designer knows (or must find out) the location of the CG on the aircraft frame (empty weight), the location of the gear bogies, the pilot eyepoint, etc. 3) The 3D modeler and the FDM designer must agree on something. A known fixed point would be a good thing to agree on. Since the CG shifts during flight, the nose tip is a good compromise. 4) As engineers, physicists, etc. (which are among our cadre of developers), we know about rotations, offsets, etc. 5) We're about ready to try this fix. We'll see how well it works. > You aren't just using the nose point. No matter how much you trick > yourselves into saying that you're only using the nose, and just > 'fixing it', you are really providing a distance reference back to another > point. We're not tricking ourselves into anything. Like we have mentioned numerous times before: We are providing the 3D model with a location in space where a known point should be co-located with. We still do (and always have) provide phi, theta, and psi, which are the same regardless of the point of reference. We know at all times the aircraft body-frame vector from the CG to the VRP (visual reference point). We know the body-to-local frame conversion matrix at any time. Thus, we know the real world location where the 3D model VRP should be placed so that the motion calculated by the FDM is properly reflected in the motion of the 3D model. Jon > It takes one point with full orientation, and another point to completely > match two reference frames. There is no way to get around that fact. What > you are really doing is having the nose point and a difference reference, and > then working everything out from that bringing everything into alignment. > That includes most importantly for visual motion to FDM motion match the CG. _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
