Re: Instancing geometry

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Angus Dorbie (dorbie++at++sgi.com)
Mon, 07 Jun 1999 10:35:42 -0700

It is obvious that any instance of an object must have some unique
transformation above it in the graph to displace it from the other
instances. So, at the very least each wheel will require a unique
translation to the correct position on the vehicle.

The only remaining question is do you rotate the wheels as part of the
'instance', or do you rotate them as part of the translation. Currently
you do the latter and that means that to rotate the wheels you must
modify 4 matrices.

To have 1 matrix for rotation just make the translates for the wheels in
four SCS' and add the same DCS->wheel as a child to each SCS.

Cheers,Angus.

Andrew Bailey wrote:
>
> Hi,
>
> I have modelled a car in MultiGen and have nearly got the wheels
> rotating. Originally the wheels were all just raw geometry, so the
> centre of rotation was not at the centre of each wheel, hence when the
> DCS for the wheels was altered the 4 wheels rotated about the origin,
> not about the wheel centre (generating some very humorous results!).
>
> What I would like to do is model the wheels as multiple instances of a
> wheel modelled at the origin, so that I can just apply the rotation to
> that wheel and the instances will all rotate as well. This should
> eliminate the need to move the centre of rotation for the DCS each time.
> I do not think this is possible though. Can the loader for MultiGen
> flight files correctly interpret instanced beads?
>
> I have tried this approach, by having one wheel at the centre of the car
> model rotating accurately, however the instances are stationary, or
> still rotating about the wrong point. I do not really want to have to
> move the centre of rotation for each wheel.
>
> Any ideas?
> thanks,
> Andrew
>
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