On Fri, 13 Feb 2004 16:52:12 -0700 Russell Suter <[EMAIL PROTECTED]> wrote:
Well, Jon, I think you already know the answer to that question. The
You probably answered that several times, but I didn't catch it in your email.
way you phrase it though implies that I somehow
believe that the modeler (aka. graphic artist) must know where the CG is. That is not the case. But, I do believe it is better
to match the model to the FDM, and not the other way around. I also
We are not really matching the FDM *to* anything. We can report any reference point with ease, and are just giving the location of the reference point that makes it easiest for agreeable placement of the 3D model.
Using the empty weight CG would not make the FDM's job any easier. Remember, the CG moves as time goes on and fuel burns off, stores are dropped, etc. It's conceivable that the fuel could be burned off of one wing tank only, which would really skew the CG. The view code will still have a 3D model with an origin at the original (empty) CG, but the FDM will be reporting a location that is perhaps several feet off to one side. So, the solution to that is that instead of the FDM calculating the offset to the VRP, the offset to the empty weight CG is calculated and reported to FlightGear instead. Very well. Yes, that would work.
However, it assumes that the 3D modeler is going to know where the empty weight CG is. Otherwise, how will the modeler know where to place the origin? You seem to say that it doesn't matter, that we will just use metadata to relate the CG (which the FDM designer knows about) to the 3D model origin (which the modeler knows about), but that will require that one or both people will need to know both things about a model. I don't see any advantage to your approach.
In this case we decided to use the VRP after debating it for a very looong time (and considering many of the same points you bring up here). In this case, the FDM designer only needs to know about what an FDM designer always knows about PLUS where the nose of the aircraft is. Easy. The 3D modeler only needs to know about what a 3D modeler knows about PLUS where the nose is. It's sort of like object-oriented design, with encapsulation. Or, like navigation: you and I don't know where each other are, but we could both meet in Chicago.
As for using an A4 FDM with a 747 model or whatever, that's a red herring.
Jon
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