[Insight-users] no. of iterations in 3D registration...

[Luis Ibanez]

Hi Shahab,

As long as you set up the optimizer to minimize, the metric should
never increase for more than one consecutive iteration. That is,
the metric can increase, but then it should decrease in the next
iteration.

There is a very very small chance that a metric can increase in
two consecutive iterations, but it requires a convoluted configuration
of the cost function.

Can you post a plot of the metric values versus iteration number,
just as it is done in the ITK Software Guide examples ?

     http://www.itk.org/ItkSoftwareGuide.pdf

How many iterations to use depends on what kind of optimizer you
are using and how large you define the step length (or its equivalent).

You may want to look at the tutorial on image registration:

at

       http://www.itk.org/HTML/Tutorials.htm

more specifically at


http://www.itk.org/CourseWare/Training/RegistrationMethodsOverview.pdf


The effect and step length versus number of iterations is also
discussed in the Image Registration chapter of the Software Guide.



Regards



    Luis



--------------------------
Shahabuddin Ansari wrote:
> Hello,
>  
> In 3D rigid registration, I am using versor transform, mean square 
> metric, and linear interpolator. The observation of the final parameters 
> shows that the metric value first decreases to a minimum and then start 
> back to increase. In my understanding, it should fluctuate around the 
> optimal value even the number of iterations are much higher (say 200) 
> then the required. Please commnets (say 50).
>  
> Thanks
> Shahab
>