Curt quipped:

> If you want to use the same 3d model for multiple FDM configurations
> which choose  different reference points, then that makes life a lot
> harder.  I think that is what the JSBsim VRP is for.

I had to laugh when reading these two sentences together. It sort of read ( to me ) 
like:

"The JSBSim VRP is for making life a lot harder."

Ha!

Some might argue that that is exactly what the VRP does. I wrote up an article on the 
VRP
for the first JSBSim newsletter (on our site). [BTW, the second newsletter is 99% 
ready, I
just need to tie up some loose ends, but conference preps have got me busier than 
usual.]

Without the VRP, JSBSim would simply report the location of the CG to FlightGear. With 
the
VRP specified in the JSBSim config file, instead of reporting the CG, JSBSim will 
report
the lat/lon/alt (the position) of the VRP instead. By convention, we say that the nose 
of
the aircraft is what we want the VRP to represent. This can be advantageous (I think)
because everyone knows where the nose of the aircraft is. This should make 3D model
placement in the scene easy.

Note that I am always open to suggestions on a better way to do this. While I feel 
that it
should not be so confusing to people (i.e. maybe there is a better way), the simple 
fact
is that given the multiple FDMs that FlightGear supports, 3D models built by many
different people, etc. maybe we would be silly to expect the simulation to do all the
work - i.e. there is some thinking one has to do for all of this.

In the end, all the FDM can do is to report lat/lon/alt. What this represents can be
[re-]opened for discussion if need be.

Jon


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