[Insight-users] fix registration parameters

[Luis Ibanez]

Hi Carmen,

That's an interesting option to consider.

It will probably make harder to keep track
of the Jacobian though. At first sight
it seems to be better to have a variety
of transforms, and select from them. Maybe
we could have both fixed centered and
non-fixed centered transforms...

As far as we have seen, the optimization
of the center of rotation doesn't add much
value to the registration. The important
contribution is to relocate the center,
even if the location is not perfect.

Note that right now you can do the equivalent
of FixParameter by selecting appropriate values
for the optimizerScales. However that will not
result in any performance (computing time)
improvement since the optimizer will keep running
in a parametric space with the total number of
dimensions.



Regards,


   Luis



--------------------------
Carmen Olmos wrote:

> Thank you for your answer Luis.
> 
> About the ongoing proposal for removing the center of rotation, what 
> about adding a method FixParameter(parameter[]) to have the option of 
> center or not center optimization - for example - without the need of 
> reimplementing the registration function?
>  
> Regards,
> Carmen
> 
> 
> */Luis Ibanez <luis.ibanez at kitware.com>/* wrote:
> 
> 
>     Hi Carmen
> 
>     You can do this by copying the code of the itkCenteredRigid2Dtransform
>     into another file, renaming the class and modifying the following
>     methods:
> 
>     SetParameters()
>     GetParameters()
>     GetJacobian()
> 
>     In SetParameters() and GetParameters() remove the insertion of the
>     center of rotation coordinates as part of the parameter array.
> 
>     In GetJacobian() remove lines 276 to 282. and renumber the
>     indexes of the Jacobian in lines 285 to 291 to be 1 and 2
>     instead of 3 and 4.
> 
>     Also in the header file replace
> 
>     itkStaticConstMacro(ParametersDimension, unsigned int, 5);
> 
>     with
> 
>     itkStaticConstMacro(ParametersDimension, unsigned int, 3);
> 
>     since now you will only have : angle, trans-X, trans-Y.
> 
>     Please let us know if you find any problem performing
>     this changes,
> 
> 
>     ---
> 
> 
>     FYI: There is an ong oing proposal for removing the center
>     of rotation from the parameter list of all the transforms.
>     In that case, most transforms will have the option of
>     a center of rotation but the coordinates of this center
>     will not participate in the optimization process.
> 
> 
>     Luis
> 
> 
> 
>     --------------------
>     Carmen Olmos wrote:
>      > Hello,
>      >
>      > I would like to perform a centered 2d registration fixing the
>     center to
>      > its initialization value (*to reduce the number of parameters to
>      > optimize*) Is there a way to fix parameters?
>      >
>      > Thanks,
>      > Carmen
>      >
>      >
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