Affine transforms - matrix algebra
Pavel Safrata
pavel.safrata at oracle.com
Tue Jul 17 08:56:58 PDT 2012
On 17.7.2012 17:03, Martin Desruisseaux wrote:
> 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 understanding.
Exactly, it seems to me that it would be tempting to interpret the 1 in
the bottom right corner as a z-axis translation..
>
> What about: AFFINE_2D (6 values), MATRIX_2D (9 values), AFFINE_3D (12
> values), MATRIX_3D (16 values)?
I think this looks better. The downside that it is probably unusable
without reading documentation ("what is the difference between matrix
and affine?")
What about MAT_2D_3x2, MAT_2D_3x3, MAT_3D_3x4, MAT_3D_4x4? Looks ugly,
doesn't it? :-(
Pavel
>
> Martin
>
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