[Insight-developers] Re: have you tested itkOrientedImage

[Leila Baghdadi]

well, I have exchanged e-mails with Bill as well,

I think we are talking about difference of definitions and how direction
cosines are used in different image formats!

I can just make sure that my start values are converted to world
(according to our definition) before I pass it to ITK,

Thanks

Leila

On Fri, 2006-10-03 at 15:13 -0600, Kent Williams wrote:
> I'm forwarding this e-mail to the ITK developers list, as I'm not sure 
> what the answer is. If you are right -- and what you've written sounds 
> plausible -- there's a problem with precedence in how the physical 
> coordinates are derived from the index.  Yet others are using 
> itk::OrientedImage without complaints.
> 
> Either your assumptions are incorrect, or the code is incorrect, and I'm 
> hoping the more informed among the developers will set us straight!
> 
> Leila Baghdadi wrote:
> 
> >Hello Kent,
> >
> >sorry again, I was just doing some testing and I see that (at least
> >according to my understanding) even though itkOrientedImage does take
> >direction cosines into account, it actually does not calculate 
> >voxel --> world correctly! I have attached my formula as well,
> >
> >can you please tell me what I am doing wrong!
> >Thanks very much
> >Leila
> >
> >for instance, 
> >
> >suppose for one of the dimensions of my image say Z
> >
> >Z --> 
> >start -2.2 
> >space 0.06
> >direction cosine 0 0 0.9
> >index 63
> >
> >so my calculation manually and from my visualization says
> >
> >(-2.2 + (0.06 * 63)) * 0.9 = 1.42
> >
> >now in itkOrientedImage.h the first thing is calculation of spacing
> >multiplied by direction cosines so matrix(2,2) = 0.054 or 0.9 * 0.06
> >which is fine but it "leaves" the multiplication of start by direction
> >cosines (i.e, -2.2 * 0.9) behind!
> >which results in
> >-2.2 + (0.06 * 63) * 0.9 = 1.202
> >
> >which is what I see printed from my itk test and I also printed values
> >from itkImageTransformHelper!!
> >
> >and I have confirmation for the other two dimensions in my image
> >  
> >
> >
> > ------------------------------------------------------------------------
> >