On Saturday 10 January 2004 02:35, Jim Wilson wrote: > Paul Surgeon <[EMAIL PROTECTED]> said: > > On Saturday, 10 January 2004 00:35, Erik Hofman wrote: > > > No, sorry. AC_EARORP is the published offset from CG to where the > > > forces act. For the F-16 that would be 35% chord (and CG is 25% chord). > > > > Just *maybe* I got it this time around. :) > > > > So any distance in the FDM is just an offset from (0,0,0)? > > > > If that is true I could offset all the distances in the FDM by an > > arbitrary value (let's say 1000 inches) and the FDM will still behave the > > same? I could pick a point 10 meters in front of the plane and measure > > everything from there too. > > In fact I could define all the distances using negative values as well > > (thinking in terms of 2nd Cartesian quadrant). > > > > The way I'm understanding all of this is that the nose of the aircraft > > CAN be used as the origin of the FDM but doesn't have to be. > > I could just as well work from the tail and just enter negative offsets. > > > > Correct? > > That is mostly correct. There is also a visual effect that occurs when you > render a 3D scene with the camera tracking an object. The point you are > tracking always appears stationary. Examples of this in FlightGear are the > "helicopter view" and the "tower view". If the origin is the nose of the > aircraft then the camera moves up and down with the nose. In the air or > from a distance this makes it look like the airplane is wagging like a > dog's tail from the nose, when it really is not. > > Take a look at the p51d as an example of an aircraft with 0,0,0 at the > nose. In the file p51d-yasim-set.xml there are several "target offset" > settings (one for each view) that represent the distance from the nose to a > very approximate center of gravity. If you want to see the effect, then > take those target offsets out. > > As you will see, this is a design weakness (my fault). The model > configuration will always need to be updated whenever more views are > configured. Note that this is a problem with the camera (the viewer code), > and not the model. It only needs to be defined per model because of the > different sizes aircraft come in. > > One solution would be to define this particular offset at a global viewer > level, and the other probably more useful solution would be to allow > parameters in the FDM config that defines the actual location where > lon/lat/alt is reported at as a distance on x/y/z axes from the aircraft's > nose. The 3D artist then only needs to know what those values are for > positioning the model and encoding the animations. > > Best, > > Jim
Heh - after just a little more thought on this: wouldn't it be nice if the origin could be made dynamic? i.e it could be changed in flight. I think the most difficult part would be deciding on how to control it - you'd probably have to change into a special mode to do it because all the input devices are already being used to control the a/c. LeeE _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
