> Short version: > > Here is the link to an updated patch which (a) corrects the > VRP precisely as Anders did with the F80C while removing the > somewhat incorrect Z offset in /Models and (b) adds several > contact points. It does not change any other pre-existing > gear, etc coordinates: > > http://139.78.95.188/flightgear/737-300/737-300.diff > > It seems that offsets specified for loading the 3D model and > the VRP accomplish the same thing. Which is the preferred > method of aligning the respective models? > -- > Reagan Thomas
Hi, Reagan: The VRP is supposed to be a way for the 3D modeler and the FDM modeler to agree on a way to make sure that the 3D model is placed exactly where it is supposed to be placed. Normally, the EOM (Equations of Motion) tracks the motion of the aircraft CG. However, the CG shifts over time, and if stores are dropped, etc., the CG can shift even more. So, if a known fixed point is reported by the FDM, the the scene generation routine knows how to place the 3D model. JSBSim uses a structural frame to determine locations of landing gear, engines, etc. for internal use - but the JSBSim modeler also knows where the nose of the aircraft is, for instance. So does the 3D modeler. So, the FDM modeler and the 3D modeler can use whatever frame they desire to. The FDM deesigner simply needs to define where the VRP is located, and the 3D modeler needs to adjust the offset value for the 3D model, so that the VRP lines up with the 3D model origin (after having been adjusted by the offset). Unfortunately, making the VRP correspond with the nose of the aircraft makes the camera look at that point, and the visual presentation of rotations looks funny - although it is correct. Now, I am thinking that perhaps a better placement of the VRP should be the initial (empty weight) CG of the aircraft, the quarter chord, or something like that. This is not a problem only with FlightGear. In particular, multi-body sims need a way to define in space exactly where the various components are located - often within a very small tolerance. I wrote an article on the VRP for an early issue of the JSBSim newsletter (see www.jsbsim.org/fsnewsletter.html). Jon ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
