[Insight-users] Registration and Spacing : Bug

[Stephan Moser]

Hi Luis

Thanks for your effort. Michael and I have studied the code today as
well and we are not sure whether the GradientFilter has its influence on
the problem, since at the moment it does not take into consideration the
spacing. We assume that the derivative is therefore calculated for a
unit spacing.

Using 40*40*40 sized images in one case with spacing 1.0
and in a second case with 2.0, we have not been able to scale the
registration process correctly so that it would yield the same result;
we would like to do this to obtain 'generally applicable' parameters for
registration of bone images.  Do you think it might be a good idea to
set the spacing of the images to 1.0 and always perform the registration
that way? We have the impression that registration can be done without
considering world coordinates, as long as the images are spaced the
same, or is there a fundamental mistake in our thought?

Thanks, Stephan


On Tue, 22 Jul 2003, Luis Ibanez wrote:

>
> Hi Michael, Carolyn
>
> We were finally able to duplicate the problem you both
> reported concerning the registration of image data with
> non-unit spacing.
>
> http://www . itk . org/pipermail/insight-users/2003-July/004215 . html
> http://www . itk . org/pipermail/insight-users/2003-July/004314 . html
>
> Using a simple registration case with translation transform,
> we found that a very small spacing causes the optimizer to
> become erratic.
>
> We are tracking this problem in order to find a fix.
>
> Our guess is that the spacing is not correctly considered
> when computing the metric derivatives in the registration
> method. A bug report has been filed in GNATS.
>
>
>   Thanks for pointing this out.
>
>
>      Luis
>
>
>
>
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