On Saturday 10 January 2004 03:09, Jon Berndt wrote: > Paul: > > The root of the problem - though it is not really a "problem" - is that the > FDM cares about modeling where the aircraft "is" in the world based on the > aircraft CG, and the 3D model wants to be in the correct spot in the world, > too, but how does one decide where to place it? Can one simply take the > FDM-reported CG and place the aircraft (0,0,0) point there? No, because the > various aircraft modelers can use any point they see fit to create their > aircraft model. There is no universal convention for that. > > We discussed here in the group some time ago a convention. The result was > that the forward most center portion of the aircraft would be the MODEL > REFERENCE POINT ("MRP" hereafter, not to be confused with the AERODYNAMIC > REFERENCE POINT). If the FDM can report the position of the MRP (and it > can), the scene code on the FlightGear side can place the aircraft very > nicely where it is supposed to be. > > This is a slight problem for the FDM, though. The FDM has to make sure that > it knows where the MRP is IN RELATION TO THE CG. This is very important to > remember that the FDM reports the lat/lon/alt of the aircraft CG. As fuel > burns off the aircraft CG moves. So, the vector to the MRP will change with > time. It's not a big problem, just a little work for the FDM - a little > work that JSBSim does not currently do. > > I hope this clears things up more. Most of this thread will find it's way > into some documentation I am writing! > > Jon > > -- > > Project Coordinator > JSBSim Flight Dynamics Model > http://www.jsbsim.org
Perhaps some published 'Standards' might be a good idea - I remember the earlier discussions about the model origin but didn't realise that a standard had been established, and so in ignorance, I haven't been following it:( Personally, I think some published standards would be a good idea and cut down on the number of problems that occur, but I realise that it's more work to be done... LeeE _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel