[Insight-developers] question regarding direction cosines

[Leila baghdadi]

Hi Kent

Thanks very much for your answer, I just got your e-mail now not sure
why,

will look through and let you know

Leila

On Thu, 2005-11-10 at 08:54 -0600, Kent Williams wrote:
> Well, the definition of the direction cosines is that they define 3 
> vectors, which define a coordinate system. The first vector corresponds 
> to the fastest moving dimension in the image, the second to the next 
> fastest, and the third to the slowest.
> 
> In other words, the direction cosines define a relationship between 
> patient space and the indices into the image data array.
> 
> I suppose it would be possible to have a file with more than 3 
> dimensions, with an organization such that the dimensions are ordered 
> T,U,X,V,Z,Y (fastest moving index to slowest) or something like that. 
> But I would worry about getting the most common case right, and work up 
> from there.
> 
> I've written an article that will be in the Insight Journal, and here is 
> a preliminary copy:
> 
> http://cornwarning.com/xfer/OrientationArticle.pdf
> 
> I hope that helps somewhat. Any more questions, feel free to ask.
> 
> Leila baghdadi wrote:
> 
> >Hi Kent
> >
> >that sounds like a good solution, the only problem with this is what if
> >the spatial dimensions with meaningful directions are *not* the first 3
> >dimensions,
> >
> >The way I envisioned this, the image could have dimensions of any order
> >
> >i.e, the three spatial dimensions can show up in any order, so that
> >would make the upper left 3x3 of an NxN not meaningful
> >
> >will work on your solution plus correct ordering, I am sure once I
> >commit the code I hear complaints about it
> >
> >
> >Thanks again
> >
> >Leila
> >On Tue, 2005-11-08 at 17:11 -0600, Kent Williams wrote:
> >  
> >
> >>Direction Matrix is NxN where N is the number of dimensions in the 
> >>image.  In general, only the first 3 directions have any spatial 
> >>meaning, and 3D images are the most common by far.
> >>
> >>I'd suggest setting the direction matrix to identity, and then filling 
> >>in the X,Y,Z (0,1,2) columns with the direction cosines representing the 
> >>3D orientation -- basically the upper left 3x3 of the matrix.  Anyone 
> >>else have a suggestion?
> >>
> >>Leila baghdadi wrote:
> >>
> >>    
> >>
> >>>Hi guys
> >>>
> >>>I am writing ImageIO classes for our specific file format (minc2) which
> >>>is like itk N-dimensional,
> >>>
> >>>I am a bit confused about how to create a correct matrix for direction
> >>>cosines,
> >>>
> >>>suppose I have an image with the following
> >>>
> >>>u,x,r,y,w,z
> >>>
> >>>so direction cosines are only for x,y,z
> >>>
> >>>the question is what is the correct way to create m_Direction of
> >>>itkImageIOBase.*
> >>>
> >>>do I create a matrix (6x3) where I have (0,0,0) (1,0,0) (0,0,0) 
> >>>
> >>>or basically how do you carry the correct index for the spatial
> >>>dimensions,
> >>>
> >>>Hopefully my question is clear if not please let me know
> >>>
> >>>Thanks
> >>>
> >>>Leila
> >>>
> >>>
> >>>_______________________________________________
> >>>Insight-developers mailing list
> >>>Insight-developers at itk.org
> >>>http://www.itk.org/mailman/listinfo/insight-developers
> >>>
> >>> 
> >>>
> >>>      
> >>>
-- 
Leila baghdadi <baghdadi at sickkids.ca>