[Insight-users] initialize VersorRigid3DTransform

[Dean Inglis]

how can I initialize a VersorRigid3DTransform for a point set
to image registration problem using the following information:
1) center of the moving points, c
2) principal axes of the moving points, e1, e2, e3
3) center of the image calculated using the ImageMomentsCalculator, cofg
4) principal axes of the image calculated using the ImageMomentsCalculator, 
p1, p2, p3

where all variables above are double arrays of size 3?  Bascally, I would 
like
 to be able to initialize the transform:
    ParametersType parameters( transform->GetNumberOfParameters() );

  //  Versor type
    typedef    TransformType::VersorType      VersorType;
    VersorType versor;

    parameters[0] = versor.GetX();   // Rotations
    parameters[1] = versor.GetY();
    parameters[2] = versor.GetZ();
    parameters[3] = 0.0;             // Translations
    parameters[4] = 0.0;
    parameters[5] = 0.0;


    transform->SetParameters( parameters );

but I dont know how the rotations should be initialized.  I could calculate 
a 3x3 rotation
matrix :
A = e * p
where e = {e1,e2,e3} and p = {p1,p2,p3} but how could that be used to 
initialize the
transform?

Dean