This partially depends on which nine parameters you want to use. Isotropic
scaling followed by rotation - or rotation followed by isotropic scaling?
If you want a parameterisation that can be encoded using the qform part of
the NIFTI headers, then I would maybe suggest taking a look at
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This code factors out the zooms and then uses SVD to take out any shears.
On Monday 14 July 2008 22:17, MCLAREN, Donald wrote:
> Is there anyway to perform a 9-parameter transformation in SPM? Basically,
> I'm wanting a transformation matrix with no shear components.
> I've tried working through different options of spm_affreg, but the
> matrices are all vastly different from the affine procedure done through
> Also, a rigid-body transform which eliminates the shear components, doesn't
> allow for any zoom components.
> Any thoughts would be appreciated.