[ODE] Simulator explodes on zero Quaternion normalisation

[GARY VANSICKLE]

> Tracing the error back in the debugger it appears that the call to
> dNormalize4 is being made from within moveAndRotateBody and is being
> done so to normalise the quaternion associated with the body.  Now at
> this point the trail goes dead for me as I don't really understand what
> a quaternion is,

A quaternion, in this context, is a 4-dimensional vector with length == 1
which represents an orientation in 3-dimensional space.

> why it should not be zero and why,

Only quaternions with length == 1 represent valid orientations.

> crucially, it is
> zero in this context.
> 

Here I can't help you, sorry.

-- 
Gary R. Van Sickle