[Insight-users] Assigning matrix and offset to VersorRigid3DTransform

[Vicente Grau]

Hi,

I am trying to initialize a VersorRigid3DTransform using a rotation 
matrix and an offset vector. The result I get is different, however, 
than if I initialize it using the 6 transform parameters. In the code 
below, I just initialize the transform once using matrix/offset, and 
then again with the corresponding versor parameters (using 
transform->SetParameters( transform->GetParameters() ); ), and the 
matrix I obtain is the inverse. This is the result:

Initial matrix: -0.1371 0.3683 0.9195
-0.2764 -0.9057 0.3216
0.9512 -0.2101 0.226
Initial offset: [-0.4294, -0.0078, 0.4992]
Initial parameters: [0.620983, 0.0370127, 0.753133, -0.4294, -0.0078, 
0.4992]

Final matrix: -0.13716 -0.276387 0.951208
0.368324 -0.90566 -0.210042
0.919524 0.321544 0.22602
Final offset: [-0.4294, -0.0078, 0.4992]
Final parameters: [0.620983, 0.0370127, 0.753133, -0.4294, -0.0078, 0.4992]

Is this normal? Am I doing anything wrong?

Thanks very much,

Vicente

***** CODE FOLLOWS *****

    typedef itk::VersorRigid3DTransform< double > TransformType;
    TransformType::MatrixType rotationMatrix;
    TransformType::OutputVectorType translation;
    rotationMatrix[0][0] = -0.1371;     rotationMatrix[0][1] = 0.3683; 
    rotationMatrix[0][2] = 0.9195;
    rotationMatrix[1][0] = -0.2764;     rotationMatrix[1][1]=-0.9057; 
    rotationMatrix[1][2] = 0.3216;
    rotationMatrix[2][0] = 0.9512;     rotationMatrix[2][1] = -0.2101; 
    rotationMatrix[2][2]=0.2260;
    translation[0] = -.4294;    translation[1] = -.0078; translation[2] 
= .4992;

    TransformType::Pointer  transform = TransformType::New();
    transform->SetMatrix( rotationMatrix );
    transform->SetOffset( translation );

    std::cout << "Initial matrix: " << transform->GetMatrix();
    std::cout << "Initial offset: " << transform->GetOffset() <<std::endl;
    std::cout << "Initial parameters: " << transform->GetParameters() 
<<std::endl<<std::endl;

    transform->SetParameters( transform->GetParameters() );

    std::cout << "Final matrix: " << transform->GetMatrix();
    std::cout << "Final offset: " << transform->GetOffset() <<std::endl;
    std::cout << "Final parameters: " << transform->GetParameters() 
<<std::endl<<std::endl;