some matrix math help

[mattd]

Hello,

It's not really a houdini specific question, more of a matrices in general question, so I hope it is not a problem posting here.

I have a program that outputs a transformation that I need to apply to a 2d image. I am trying to understand how to convert the format it outputs to a transformation I can use in a COP. Here is the description of the output of the program that I am looking for:

Affine: (AffineTransform) An affine transformation is defined as:

Tμ(x) = A(x − c) + t + c,

where the matrix A has no restrictions. This means that the image can be translated,

rotated, scaled, and sheared. The parameter vector μ is formed by the matrix

elements aij and the translation vector. In 2D, this gives a vector of length 6:

μ = (a11, a12, a21, a22, tx, ty)T .

So I need to figure out how that 2x2 matrix and the tx and tx can get converted into values usable in a transform COP. I know that the explodematrix expression does what I need, but how do you work with the values I am getting?

oh, and I need to do all of this with expressions, I can't use a VOP.

Thanks for any help.

MD

[mattd]

nevermind, I figured it out, I think

it's

[a11 a12 0]

[a21 a22 0]

[tx ty 1]

I keep answering my own posts, but hey, it helps to formulate the question to solve it.

Thanks

MD