[vtkusers] Re: Clarification: vtkImageReslice->reorienting a volume

[David Gobbi]

On Mon, 12 Jun 2000, Audrius Stundzia wrote:

> Hi David,
> 
> Thanks for your prompt reply. Much appreciated.
> 
> >If you just want to change the orientation, just use
> >SetResliceMatrix but not SetResliceTransform.
> >
> 
> Got it. Thanks.
> 
> >The 3x3 portion of the matrix should contain the direction cosines.
> 
> Got this too. However, a clarification of the man pages entry for
> void SetResliceAxes (vtkMatrix4x4 *)
> would be very helpful:
> o The standard (i,j) = (row,column) convention is being used?

Yes, as per vtkMatrix4x4.

> o The column vectors are those of the old axes? or the new axes?

The column vectors are the old axes.  The SetResliceTransform method
works in the same way, it is a transformation from the new coordinate
space to the old coordinate space.  The interpolation algorithm naturally
works in that direction.  

> Ie., x_p = Rx where R is the rotation matrix, are the column vectors the 
> axes associated with x or with x_p? Looking at Eqn (3-13) in the book, I 
> think column vectors are the "new, target" axes associated with x_p. 
> Correct?

Other way around.  But you should really try some simple test cases to
ensure that you're doing it the right way.

> Finally, I think vtkImageReslice is a most useful contribution to vtk.

Thanks.  It was my first VTK class, and I kind of let it grow out of
control.  It still doesn't do anti-aliasing though...

 - David