> There is no choice in the matter. The center of the aircraft is the center > of the aircraft and is the simplest point of agreement between the visual and > the FDM, and simplest point of calculations for both. You can use the nose as a > reference point, but you still better make very sure your nose is > the same distance visually from POS as it is calculated in the FDM if you > want them to match.
Alan: I appreciate your thoughtful inputs, but I suspect you are missing the point, which has a long history here. Initially, we had very large problems and obvious errors in placing the 3D model of the aircraft because the FDM was tracking the CG and the 3D modelers were creating their models based on all sorts of different frames of reference. Then FlightGear was placing the 3D models in the scene with the 3D model origin (0,0,0) at the FDM-reported CG. If the aircraft was oriented at PRY = (0,0,0) there was only a translational error. If the aircraft had any nonzero rotational component, things were magnified. When the aircraft *flight* modelers create a flight model for an aircraft, there is a prerequisite for having intimate knowledge of the aircraft layout. Usually, that means we have a 3-View drawing and oftentimes we have coordinate points of specific items on the aircraft in the manufacturers structural frame (X positive out the back, Y positive out the right side, origin often near the nose or just ahead of it). The aircraft modeler is free to choose their model origin, but the axes must line up with the structural frame. The 3D modeler has no clue about (and probably doesn't care to know about) where the CG is - and that's fine. The FDM and the 3D model, though, *do* need to agree on a common MRP (Model Reference Point) that the FDM can supply to the FlightGear scene code for proper placement of an aircraft. Once that point is agreed upon, it's not a big problem at all for the FDM to send to FlightGear the exact location in world space of the MRP. No matter what the orientation of the aircraft, the 3D model will always have its CG in the correct place if the FDM properly reports to FlightGear the real-world location of the MRP. We (FDM) can do this because, as I've said before, we know where the CG is, and we know where the MRP is in reference to the CG. Jon _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
