Re: [eigen] Euler-angles and partial reductions API design

```And, now that I understand why you have an AngleAxis class, I also understand
why you naturally added EulerAngles as a pure convenience, even without
trying to make it as fast as possible. Now I agree it's always a good thing
to have.

Cheers,
Benoit

On Saturday 19 July 2008 01:08:35 Benoît Jacob wrote:
> Ah OK, I didn't realize that. Thanks for the explanation.
>
> Benoit
>
> On Saturday 19 July 2008 00:58:30 Gael Guennebaud wrote:
> > well, I would prefer to keep the AngleAxis class, for various reasons.
> > One of them is that we also have the Quaternion, so you create an
> > angle axis and it gets automatically converted to whatever you want:
> >
> > Quaternion q = AngleAxis(a,b);
> > Matrix m = AngleAxis(a,b);
> >
> > that is pretty nice IMO, and Matrix3f::Rotation(a,b)  will never be as
> > explicit as AngleAxis(a,b), isn't it ?
> >
> > I also have to say that since two angle-axis cannot be directly
> > composed, AngleAxis(a,b) * AngleAxis(c,d) must convert the two
> > operands to a quaternion or a matrix. In practice, converting them to
> > Quaternion is always faster even if at the end you want a matrix (and
> > even if you have special AngleAxis to rotation matrix conversion
> > functions for rotation around basis axes).
> >
> > gael.
> >
> > > one more remark,
> > >
> > > if we drop EulerAngles then we can also drop the AngleAxis class in
> > > favor of just "rotation" functions, not classes. so the above snippet
> > > becomes
> > >
> > > Matrix3f m2 = Matrix3f::rotation(a1, Vector3f(1,0,0))
> > >              * Matrix3f::rotation(a2, Vector3f(0,1,0))
> > >              * Matrix3f::rotation(a3, Vector3f(0,0,1));
> > >
> > > I think that's nicer!
> > >
> > > Cheers,
> > > Benoit

```

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