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Ashburner John (PSYCHOLOGY) wrote: > The Q-form is a bit limited. In SPM, I usually set it to be as close as > possible to the S-form, and usually only the S-form is used by > spm_get_space. Anyone who has worked with CT data will notice that > shears would be desirable for representing the voxel-to-world mappings. > Many CT images are skewed. Ah, so then Ged's point (what's the use of the Q-form in the 1st place) is a very good one. There are no specifications as to what the Q-form and S-form should be used for, respectively. But was there a rationale for having 2 separate forms and making 1 more limited? Things that I would think it could be handy for would be: coronal or saggital slices instead of axial. Those positionings are rigid-body transformations, and by using the Q-form for those, you keep your S-form free for more demanding alignments. best Alle Meije