Hi,
the code from makeRotate explains it best:
--8<--
void Quat::makeRotate( value_type angle, value_type x, value_type y,
value_type z )
{
const value_type epsilon = 0.0000001;
value_type length = sqrt( x*x + y*y + z*z );
if (length < epsilon)
{
// ~zero length axis, so reset rotation to zero.
*this = Quat();
return;
}
value_type inversenorm = 1.0/length;
value_type coshalfangle = cos( 0.5*angle );
value_type sinhalfangle = sin( 0.5*angle );
_v[0] = x * sinhalfangle * inversenorm;
_v[1] = y * sinhalfangle * inversenorm;
_v[2] = z * sinhalfangle * inversenorm;
_v[3] = coshalfangle;
}
--8<--
You can see that the length of the vector you use for rotation is
already accounted for, i.e. normalising the vector would not change
anything.
The only exception is for very small vectors, if length < epsilon you
will get a zero rotation. If you think your vector with length < epsilon
is a valid rotation vector, then normalising it before calling
makeRotate could make a difference.
I'd normally associate such a small rotation vector, if it is coming
from other code, to indicate a zero rotation anyways, but I don't know
your application.
regards
jp
Vincent Bourdier wrote:
> Hi
>
> First, yes it is the vector OF rotation, sorry for the mistake...
>
> And when I speak about normalizing, I'm just thinking of making a
> vector.normalize()... with that operation, length of the vector will be
> 1, even if the vector is close to 0 0 0...
>
> I just want to use this vector to set the rotation vector of the Quat...
>
> To be more clear : I have a Quat with a rotation vector which is very
> very little... I ask if normalizing this vector will make a difference ?
> and why ?
>
> Thanks,
>
> Regards,
> Vincent
>
> 2008/3/19, J.P. Delport <[EMAIL PROTECTED]
> <mailto:[EMAIL PROTECTED]>>:
>
> Hi,
>
> I'd like to help, but don't know what you are asking...
>
>
> Vincent Bourdier wrote:
> > Hi all,
> >
> > I just have a little question, because I'm not sure of something
> about
> > quat :
> >
> > I have to quat q1 and q2
> >
> > To pass form q1 to q2 I've made q = q1.inverse()*q2
> >
> > But even if the result angle looks correct... the vector or rotation
> > looks very little :
>
> Is this vector _of_ rotation? Where is this vector coming from?
>
>
> >
> > vec : 2.71051e-020, -2.71051e-020, 1.0842e-019
> >
> > Sometimes it is 0 0 0...
> >
> > Do I have to get the vector, normalize it and set it to the quat
> ? or is
> > the vector lenght important ?
>
> Normalising 0 0 0 (or something close to it) is bound to give you
> headaches. What do you want to use the vector for?
>
> Please provide more context.
>
> jp
>
> >
> > thanks,
> >
> > regards,
> > Vincent
> >
> >
> >
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