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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] geometry module...
- From: Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>
- Date: Fri, 19 Mar 2010 20:01:43 +0100
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On Fri, Mar 19, 2010 at 7:44 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
>> - make UniformScale * Translation return a Translation
>
> I don't understand that. UniformScale * Translation should return the
> composite transformation, that consists in first translating and then
> scaling. This is not a translation!
Well, maybe the bigger problem is that we do not yet have expressions
in the transformation chain. A translation is not even a
transformation but it behaves as such since
Vector = Translation * Vector
is a valid operation - i.e. translations behaves like a transformation
matrices. And given
Vector = Scaling * Translation * Vector
which can be written as
Vector = (Scaling * Translation) * Vector = OtherTranslation * Vector
I considered returning a translation - in particular since
Translation * Vector
is way more efficient than
ProjectiveTransformation * Vector.
Maybe now I managed to maximize confusion but I agree that such a
trivial fix is not really a fix and thus I will leave it alone for the
moment.
- Hauke