Affine transforms - matrix algebra

Martin Desruisseaux martin.desruisseaux at
Tue Jul 17 08:03:10 PDT 2012

Le 17/07/12 16:50, Pavel Safrata a écrit :
> I've just realized that the 3x3 matrix is wrong (or at least more 
> confusing than useful). It would be good for representing a 3D 
> transform without translation (which we don't really need to do), but 
> not for the intended representation of 2D transform with translation. 
> So I'm taking back the addition of MAT_3x3.

I though that MAT_3x3 was just a convenience for MAT_2x3 with a [0 0 1] 
row added, like MAT_4x4 is a convenience for MAT_3x4 with [0 0 0 1] added?

Thinking more about it, maybe the original MAT_2D, MAT_3D, etc. names 
were less confusing after all, since MAT_3x3 may suggests "extract from 
the 4x4 matrix a sub-matrix of side 3x3", which is not quite my initial 

What about: AFFINE_2D (6 values), MATRIX_2D (9 values), AFFINE_3D (12 
values), MATRIX_3D (16 values)?


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