Hi Stamatis - no, the 4th dimension is not time. This is called a
homogeneous transformation.
It allows you to represent rotations, translations, skews, scales etc. in
a single matrix, which is not possible in only 3D.
So
[X'] [X]
[Y'] = A [Y]
[Z'] [Z]
[1] [1]
where A is your homogeneous transformation matrix.
For details about this, just stick
"homogeneous transformation" into google
e.g,
http://prt.fernuni-hagen.de/lehre/KURSE/PRT001/course_main/node13.html
Tim
On Sun, 3 Oct 2004, Stamatis Sotiropoulos wrote:
> On Fri, 1 Oct 2004 20:59:55 +0100, Tim Behrens <[log in to unmask]>
> wrote:
>
> >Hi -
> >
> >I would have to go back and check the paper to be sure about what matrix
> >Danny is referring to, but the .mat file is the transformation matrix
> >between the original and transformed space, and yes it is an affine
> >transformation matrix.
> >
> >Cheers
> >
> >Tim
> >
>
> Hi Tim,
> the .mat file produced by FLIRT contains a 4x4 matrix. What is the 4th
> dimension of this matrix? Time?
>
> Thank you in advamce,
> Stamatis
>
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Tim Behrens
Centre for Functional MRI of the Brain
The John Radcliffe Hospital
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