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 _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
