[MINC-users] Affine transformation matrix

[Claude LEPAGE]

Andrew,

Why not do a -lsq12 transform while disabling scales via the
-w_scales parameter to minctracc?

Claude


>
> Hi Aaryani,
>
> You are asking a pretty loaded question here. If the scaling is small
> (say 1.001) then I wouldn't expect removing it will make much
> difference, of course there will still be a difference but it probably
> will be tolerable.
>
> Remember also that an .xfm is really just an affine transformation
> matrix that can be expressed in a many different combinations of
> rotations, translations, scales and shears. xfm2param just gives you
> one of these solutions based upon a set of assumptions (rotations all
> less than 90deg, etc).
>
> As for changing the rotations and translations accordingly, the answer
> is definitely yes, but the matrix algebra involved in this is going to
> get pretty ugly pretty quick and in any case will not be the same as
> the original transformation once the scaling is removed. My suggestion
> if you really want to do this is to recover the transformation type
> you want using minctracc from the outset. In your case this would be
> done via the -lsq6 argument, or perhaps lsq7.
>
> a
>
>
>
> On Wed, Jun 22, 2011 at 10:22, Aaryani Tipirneni <atipirne at stanford.edu> wr=
> ote:
> > =A0I have a basic question - As we know, If we do affine registration usi=
> ng mritotal to the atlas, we will get a .xfm file with the translations, ro=
> tations, scaling and shearing. If I now want to remove the scaling from the=
>  .xfm matrix so that the coregistered data has the same scaling as the orig=
> inal data (to avoid stretching and shrinking), do you expect to still coreg=
> ister well? Do I have to change even the rotations and translations accordi=
> ngly?
> _______________________________________________
> MINC-users at bic.mni.mcgill.ca
> http://www.bic.mni.mcgill.ca/mailman/listinfo/minc-users
>