[MINC-users] minctracc with mask: objective function startsat0.0: what to do?

[Andrew Janke]

Audette, Michel <Michel.Audette at medizin.uni-leipzig.de>:
> please remind me of the relationship between step-size, w_rotations, and w_translations?

There is no direct relationship?

The step size refers to the distance between the nodes of the 3D
lattice of points that is "overlaid" on the image. minctracc then only
takes data from these points during the registration of the images. Of
course if the input images are blurred then it will "get data" from
other voxels due to the effect of blurring.

The w_ parameters merely set the initial granularity of the simplex
function that is used during optimisation.  ie: if w_translations = 1
then one iteration of minctracc will shift an image relative to
another by approx 1mm. w_rotations is a tad more difficult as you must
remember that the rotation experienced at the centre of the image is a
lot less than at the edges.

Thus the default values for w_rotations give approx a 1mm movement at
the edge of a standard sized head when rotating about the Centre of
Mass.


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Andrew Janke   (a.janke at gmail.com || http://a.janke.googlepages.com/)
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