Re: Ground limit and 3D model

On 5/21/05, Erik Hofman <[email protected]> wrote:
> Sam Heyman wrote:
> > I have now nearly finished implementing our project UAV "Manta" in
> > Flightgear and am very satisfied with the result.
> >
> > There is one thing though which I am not quite sure about and that is
> > the position of the 3D model. It seems to be positioned correctly and
> > flies pretty accurately. The problem, however, is when I start the
> > flight on the runway the aircraft is placed right on the edge, rather
> > than on the zebra-crossing...
> > It also has a tendency of going "underground" easily.
> >
> > Should a correctly placed 3D model stay above ground at all times?
> > Does this mean that my 3D model is offset from the FDM coordinates? (the
> > model is only 2.2m span, so is much closer to the runway).
> 
> This sounds as if you have the X and Y offset switched somewhere,
> causing the aircraft to be modeled th the right instead of forward.
> 
> If the gear contact points are defined (which they should be since it
> does stay on the runway) then these contact points clip the plane to the
> ground.

Is there any way of telling whether the aircraft is correctly
positioned? My 3D model is centred in the middle of the screen and
when I zoom it remains in the centre.
However, it sometimes flips-over and lies on its back, underground...
which seems to hint something isn't quite right.

> 
>  > Where is the center of the FDM coordinates placed when you start the
>  > flight on the  runway?
> 
> In case of JSBSim there is on imaginary center (0,0,0) which could be
> placed at one of the known locations of the aircraft.
> 

Yes I understand this point and my FDM origin is at the tip of the
nose. What I mean is when the aircraft is loaded on the runway, where
is it placed? Is the origin of the FDM placed on the zebra-crossing?

My main problem is that I want to be absolutely sure my 3D model is
correctly centred, and this I am finding quite tricky. Is there for
exemple a way of localising the FDM origin?

Thanks, Sam

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