[Insight-users] point to point registration - itkMatrix to vtkMatrix, AffineRegistration

[Boettcher, Dr. Peter]

Hello

 

I would like to fit a cylinder on to the medial condyle of the femur reconstructed based on CT images within vtk. For that purpose I pick several points on the surface of the condyle within vtk and pass them as the fixed point cloud to a point to point registration like the one in example\patented\ iterativerClosestPoint2 or 3. Second I generate a cylinder 3D-object in vtk (vtkCylinderSource) and extract its points. They a passed to the registration as the moving point cloud. In contrast to the examples in the itk-book I use AffineTransformation, because I need scaling in addition to translation and rotation of the cylinder. 

 

Here comes my first question: is it possible using AffineTransformation without shearing? I am only interested in translation, rotation and scaling. I woul prefer using AffineTransformatino because its output is more familiar to me than the other transformer.

 

At the end of the registration (at the moment with shearing) I extract the transformation matrix and translate it to vtk:

 

vtkMatrix4x4 *matrixVTK = vtkMatrix4x4::New();

  

  TransformType::MatrixType matrixITK =  transform->GetMatrix();

  TransformType::OffsetType offset = transform->GetOffset();

 

            matrixVTK->SetElement(0,0,*matrixITK[0,0]);

            matrixVTK->SetElement(0,1,*matrixITK[0,1]);

            matrixVTK->SetElement(0,2,*matrixITK[0,2]);

            matrixVTK->SetElement(0,3,offset[0]);

            matrixVTK->SetElement(1,0,*matrixITK[1,0]);

            matrixVTK->SetElement(1,1,*matrixITK[1,1]);

            matrixVTK->SetElement(1,2,*matrixITK[1,2]);

            matrixVTK->SetElement(1,3,offset[1]);

            matrixVTK->SetElement(2,0,*matrixITK[2,0]);

            matrixVTK->SetElement(2,1,*matrixITK[2,1]);

            matrixVTK->SetElement(2,2,*matrixITK[2,2]);

            matrixVTK->SetElement(2,3,offset[2]);

            matrixVTK->SetElement(3,0,0);

            matrixVTK->SetElement(3,1,0);

            matrixVTK->SetElement(3,2,0);

            matrixVTK->SetElement(3,3,1);

 

Using 

m_actorCylinder->SetUserMatrix(matrixVTK);

m_renWin->Render();

 

shows the result in 3D (vtk).

 

The script runs well, but the results are not what I expected. Especially the scaling factors are well too small. Moreover I doubt that the conversion from the itk-matrix to the vtk-matrix is

right the way I did. It seems for example, that the matrixVTK[0,1] does not correspond to the matrixITK[0,1]. To translate the moving 3D object onto the fixed 3D object in vtk do I have to invert the transformation I got in the itk?

 

Last but not least I implemented a registration observer and its class to monitor  the registration process in 3D by updating the vtk-pipeline - but the observer is not invoked during the registration process:

            // Observer

            CommandIterationUpdate::Pointer observer = CommandIterationUpdate::New();

            optimizer->AddObserver( itk::IterationEvent(), observer );

 

I would deeply appreciate any help or comment

 

Peter.

 
------------------------------------
P. Böttcher, Dr med vet, DipECVS
European Veterinary Specialist in Surgery
Klinik für Kleintiere 
Universität Leipzig 
An den Tierkliniken 23 
D-04103 Leipzig (Germany)
Tel: +49-341-9738700 
Fax: +49-341-9738799
email: boettcher at kleintierklinik.uni-leipzig.de

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