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Well, you could get this matrix for both images, an then matrix-divide
them I guess?
 
V1=spm_vol('file1.nii')
V2=spm_vol('file2.nii')
 
V2.mat/V1.mat
 
When I remember the math well this matrix should map file1 to file2 in
worldspace, if that is what you are after.
 
check 'help mrdivide' and 'help mldivide' to be sure, I just do this
math from the head right now.
 
But when you want to map one image to another, why dont you use
coregister > estimate in SPM, which is the normal way? You would not
have to bother with matrix algebra altogether ...
 
Good luck,
 
Bas
--------------------------------------------------
Dr. S.F.W. Neggers
Division of Brain Research
Rudolf Magnus Institute for Neuroscience
Utrecht University Medical Center
Visiting : Heidelberglaan 100, 3584 CX Utrecht
              Room B.01.1.03
Mail     : Huispost B.01.206, P.O. Box 85500
             3508 GA Utrecht, the Netherlands
Tel       : +31 (0)88 7559609
Fax      : +31 (0)88 7555443
E-mail  : [log in to unmask]
Web    : http://www.neuromri.nl/people/bas-neggers
             http://www.neuralnavigator.com
<http://www.neuralnavigator.com/> 
--------------------------------------------------

 


________________________________

	Van: [log in to unmask]
[mailto:[log in to unmask]] Namens Dan Golding
	Verzonden: vrijdag 21 mei 2010 15:13
	Aan: Neggers, S.F.W.
	Onderwerp: Re: [SPM] Finding affine transformation parameters
	
	
	Thanks, but would you mind explaining this in a bit more detail?
	
	I'm don't quite see the difference in loading an image using
spm_vol(spm_select) and using spm_vol('filename.nii') which is how I
have been doing it. The .mat field gives information about the
individual images, but not about how to transform one image to another
which is what I am looking for. Unless I have misunderstood?
	
	If you could please explain to me how I can coregister one nifti
image to another, and get the affine transformation matrix describing
that transformation, I would greatly appreciate it.
	
	Thanks
	Dan
	
	
	On Fri, May 21, 2010 at 2:54 PM, Neggers, S.F.W.
<[log in to unmask]> wrote:
	

		V=spm_vol(spm_select);
		
		V.mat
		
		
		--------------------------------------------------
		Dr. S.F.W. Neggers
		Division of Brain Research
		Rudolf Magnus Institute for Neuroscience
		Utrecht University Medical Center
		Visiting : Heidelberglaan 100, 3584 CX Utrecht
		             Room B.01.1.03
		Mail     : Huispost B.01.206, P.O. Box 85500
		            3508 GA Utrecht, the Netherlands
		Tel       : +31 (0)88 7559609
		Fax      : +31 (0)88 7555443
		E-mail  : [log in to unmask]
		Web    : http://www.neuromri.nl/people/bas-neggers
		            http://www.neuralnavigator.com
		--------------------------------------------------
		
		
		
		> -----Oorspronkelijk bericht-----
		> Van: SPM (Statistical Parametric Mapping)
		> [mailto:[log in to unmask]] Namens Dan Golding
		> Verzonden: vrijdag 21 mei 2010 14:43
		> Aan: [log in to unmask]
		> Onderwerp: [SPM] Finding affine transformation
parameters
		
		>
		> Hi,
		>
		> I would like to find the 12 parameters for an affine
		> transformation between two nifti images. I have been
looking
		> into using spm_coreg and spm_matrix but I couldn't
quite
		> understand how to use them form their help. spm_coreg
outputs
		> 6 parameters, I'm not sure what these 6 are?
		>
		> Also is there a function that does the reverse of
spm_matrix,
		> i.e. one that can take an affine transformation matrix
and
		> split it into 3 rotations, 3 scalings etc...?
		>
		> Thanks
		> Dan
		>
		
		
	
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