Jon Berndt writes:
>>
> We all know that we can rotate the 3D model correctly, but the issue is
> the translation. JSBSim reports the location of the CG, which is NOT the
> translation for any point on the aircraft, but ONLY the CG.
>
> So, the solution is that JSBSim (and other FDMs) could report the location
> of the 3D model origin at every frame for rendering purposes. OR,
> FlightGear could derive it - given it may have more intimate knowledge of
> the 3D model AND the CG. True? Problem is, the FDM guys don't KNOW what
> point will be chosen for the 3D model origin. The FDM could report the
> position of any point in our own coordinate system. If we gave the
> location of the nose as a commonly known reference point, then I believe
> the rendering code could have that location to use as its "pivot point".
>
> I hope I understand the problem correctly, and that this isn't muddying
> the water.
I think that when we add colision detection into the mix the most
sensible reference point is the center of the bounding volume
collision includes wheel-runway contact points ect
we used the static center as a 'close enough kludge' historically
but if we are going to change the location IMHO we should do so
in a way that increases accuracy. ie the nose is further away from
the geometric center then the published static center
So to summarize the needed locations discussed so far
1:center of gravity
used by FDM
2) aerodynamic center
used by FDM
3) eye location
used to render the scene
4) geometric center
used by SSG and collision detection
Of these the one that corresponds to 'everday speak'
and common engineering usage is (4)
Norman
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