[Insight-users] Registration and Spacing : Bug

[Luis Ibanez]

Hi David,

Another possible suspect is the computation of Jacobians
in the transforms. However, the translation transform
used by Carolyn and Michael have a quite simple Jacobian,
which leaves few room for error.

In the case you mention, the VersorRigid3DTransform is used,
this transform has a rather complex Jacobian, which make it
a better candidate for failure.

It is not clear at this point if both effects of increasing
cost-function are originated from a single error.

Would you observe the same miss-behavior of the optimizer
if you replace the VersorRigid3DTransform with a simple
Translation  ?



Regards,



    Luis



---------------------
David Holmes wrote:
> Luis-
> 
> I am not sure that it is simply an issue with non-unit
> spacing.  I have had this problem for some time (refer
> to
> http://www . itk . org/pipermail/insight-users/2003-February/002637 . html).
>  To confirm the problem again, I used the
> ImageRegistration8.cxx example with a very simple
> dataset and show the same results (i.e. the cost value
>  increases).  In my case, the spacing is [1,1,1] for
> both fixed and moving.  I've fooled with parameters. 
> That is not the problem.  I've run both simple and
> multi-resolution registration.  That is not the
> problem.
> 
> thanks
> 
> david
> 
> 
> --- Luis Ibanez <luis . ibanez at kitware . com> 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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> 
> 
> 
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