[Insight-users] Re: Regarding One of the Application

[Luis Ibanez]

Hi Shekhar


1) This application is unfortunately quite missleading.
   (we should probably remove it from the repository).

   It is only illustrating how to put together all the
   components of the registration framework.  They are
   not fine tunned for working together, so it will be
   useless to attempt to perform a real registration
   with this application.

   If you are looking for an application to try, please
   look at

    LandmarkInitializedMutualInformationRegistration


2) When you change the tolerance in the RegularStepGradient
    descent optimizer you may force the optimizer to look
    for a more stable solution, and this can take more
    iterations.  It doesn't necessarily means that you
    are going to get a different answer, it simply means
    that the precision of the answer has been verified
    further.

    Note that this optimizer returs the criteria that
    triggered the process to stop. Please call
    GetStopCondition() just after the registration finish.
    That will tell you if you used all the iteration or
    stopped due to the step length size, or due to the
    magnitude of the derivative.


3) If you want to write you own optimizer, please take
    a look at the superclasses of the RegularStepGradient
    descent. There are a number of standard methods that
    you may have to implement. In general the optimizer
    receives an array of parameters (this is the parametric
    space for the optimization), and has access to a cost
    function (that in image registration is the image
    metric). You should decide if your optimizer requires
    the metric to compute derivatives or not.

    Make sure that you invoke IterationEvents at each
    iteration of your optimizer, that will allow you to
    connect an observer and follow the progression of your
    optimizer at run time.




   Regards,


      Luis



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Dwivedi, Shekhar (Research, Non-ge) wrote:

> Hi luis ,
> 
> I have a question regarding one of the example in InsightApplications directory.
> 
> 1- 
> In the directory InsightApplications/ImageRegistration
> 
> There is a interface in which there is a choice to select any one of the optimizer among
> Regular Step , Gradient Descent , Conjugate Gradient.
> 
> I am wondering whether this functionality is implemented or not.As I have seen the code where the optimizers is
> selected from the file liImageRegistrationConsoleBase.cxx , there is no parameter setting for any of the optimizers.
> I have checked other files as well ,  please clarify the doubt that if the optimizers are selected then where is the 
> exact location of setting up of the parameters for the corresponding optimizer.
> 
> 2-
> 
> I have one more question regarding the Regular Step Gradient Descent optimizer.
> 
> I tried to include the tolerance factor also for this optimizer for my 3D image registration , but the output was same as 
> without tolerance factor and it took more time for the registration , what may be the likely reason for this.
> 
> Finally can u tell me which all parameters of Conjugate Descent optimizer are required to be called for image registration.
> 
> 3- 
> 
> If I plan about writing my own optimizer(specific to image registration) then what all things I must consider beside the
> implementation.
> 
> Yours,
> Shekhar. 
>