[Insight-users] Re: [Insight-developers] bug report on DeformableModelSimplexMesh application

[Defeng WANG]

Hi, Leila,

Thanks for your reply. It seems that the parameters in the UI of
DeformableModelSimplexMesh are not related to the gradient calculation. I
read the source code involved in DeformableModelSimplexMesh. As for the
gradient calculation, three filters are used successively as follows,

  m_GradientMagnitude->SetInput(m_CastImage->GetOutput() );
  m_GradientMagnitude->SetSigma(0.5);

  m_SigmoidImage->SetInput( m_GradientMagnitude->GetOutput());
  m_SigmoidImage->SetOutputMinimum(0);
  m_SigmoidImage->SetOutputMaximum(1);
  m_SigmoidImage->SetAlpha(230);
  m_SigmoidImage->SetBeta(1300);

  m_GradientFilter->SetInput( m_SigmoidImage->GetOutput());
  m_GradientFilter->SetSigma( 0.5);


I have taken a look at the final gradent image. It seems that it is good 
enough to describe the
edge or boundary of a sphere. So what do you think of this problem existing
in this simple example?


Look forard to your response.

Best wishes,
Defeng

----- Original Message ----- 
From: "Leila Baghdadi" <baghdadi at phenogenomics.ca>
To: "Defeng WANG" <dfwang at cse.cuhk.edu.hk>
Cc: <insight-developers at itk.org>; <insight-users at itk.org>
Sent: Thursday, January 31, 2008 10:54 PM
Subject: Re: [Insight-developers] bug report on DeformableModelSimplexMesh 
application


> Hi Defeng,
>
> Yes I have used that code many a times. I am not sure if I understand
> what you mean by "it does not converge".
>
> My understanding of deformable models is
>
> 1. you must make sure your gradient image is created properly. Use
> paraview to look at the vector image
>
> 2. you must play with the parameters to get the model to converge,
>
> This is a specific type of deformable models which uses simplex mesh.
> I suggest you read about this algorithm first. This is developed based
> on the paper by Herve Delingette of INRIA france.
>
>
> Leila
>
> On Thu, 2008-31-01 at 22:29 +0800, Defeng WANG wrote:
>> Hello, ITK users and developers,
>>
>> I found that DeformableModelSimplexMesh, provided in
>> InsightApplications-3.4.0, does not converge. It seems that the
>> deformable mesh will not stop near the boundary of one object to be
>> segmented. I tried a very simple volume data set containing a sphere
>> only. The initial mesh I used is a spherical simplex mesh inside it.
>> However, by increasing the number of iterations, the mesh will
>> continue to expand until it reaches outside of the image and the
>> program reports error.
>>
>> Is there anybody tried this program successfully before? Or anybody
>> knows how to adjust the parameters properly to get right segmentation?
>>
>> Best wishes,
>> Defeng
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