--- Andy Ross <[EMAIL PROTECTED]> wrote: > 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.
This is true of the subject 3D model reference point, but not of the JSBSim aero reference point. That point needs to be at least close to the same point used to produce the coefficients you have. > > 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 > > __________________________________________________ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
