Apparently simple questions often have the most difficult answers. This
one is a bit like computing the average location of San Francisco,
Melbourne, Chicago and Florence, but where the answer has to lie on the
Earth's surface. Actually, it is a bit more difficult than that - and
it would require some way of measuring distances to be defined (a
metric).
Probably the easiest approximation would be to use a Procrustes method,
or similar, in order to factorise out a global rigid body transform and
then average the rigid/affine transforms as described by eg Woods. The
displacements could be averaged by assuming a small deformation
framework, in which displacement fields can be added or subtracted.
A model whereby displacement fields can be added and subtracted is not
really correct, but doing it properly would need a load of maths.
Best regards,
-John
References:
http://en.wikipedia.org/wiki/Procrustes_analysis
Title: Characterizing volume and surface deformations in an atlas
framework: theory, applications, and implementation
Author(s): Woods, RP
Source: NEUROIMAGE Volume: 18 Issue: 3 Pages: 769-788 Published:
MAR 2003
On Tue, 2009-06-23 at 05:37 -0700, kamran kazemi wrote:
> Dear SPMers
> How one can calculate avrage deformation from deformation matrixes
> (*.nii fieles obtained from deformation toolbox)?
>
> Kind Regards
> Kamran
>
--
John Ashburner <[log in to unmask]>
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