Matrix Math wiki question

[computersarecool]

Hi,

In the documentation for the Geometry COMP it says:

if we use the ‘multiply vector on the right’ (column vector) convention, a transform order of Scale, Rotate, Translate would be written as translate * rotate * scale * vector.

This makes sense to me.

However, in the documentation for the pre-Transform page it says that:

In terms of matrix math, if we use the ‘multiply vector on the right’ (column vector) convention, the equation would be preXForm * xform * vector.

For the preXform isn’t this backwards? Shouldn’t the preXform first be multiplied by the vector?

[malcolm]

The equation is correct. The naming of it can be a little strange depending on how you look at it. It’s applying this transformation to the COMP before the COMP’s regular transform. It’s not applying it to the vector before the COMP’s regular transform.

[computersarecool]

I usually think of transformation matrices in terms of “original coordinates” so the word “vector” may be confusing me here.

For the transform tab, when it says “a transform order of Scale, Rotate, Translate would be written as translate * rotate * scale * vector.” does vector mean the original vertex information? (I.e. how the geometry inside would be moved)

In this case if we wanted to pre-transform the geometry by scaling it up by 2 and rotating it 90 degrees, wouldn’t we have to do that to the original vertex information (i.e. vector), then apply the regular transform to this new value?