Error using LandmarkBasedTransformInitializer with BSpline transform

[ctorti]

Hello,

I am aware of sitk.BSplineTransformInitializer(image1, transformDomainMeshSize, order) for performing BSpline registrations, but I am trying to initialize the registration using LandmarkBasedTransformInitializer.

Following is how I attempt to obtain a landmark-based transform for a 'rigid', 'affine' or 'bspline' transform:

def GetLandmarkTx(FixIm, MovIm, FixPts, MovPts, 
                  Transform='rigid', NumControlPts=8):
    import SimpleITK as sitk
    
    if Transform == 'rigid':
        SitkTransform = sitk.VersorRigid3DTransform()
    elif Transform == 'affine':
        SitkTransform = sitk.AffineTransform(FixIm.GetDimension())
    elif Transform == 'bspline':
        SitkTransform = sitk.BSplineTransform(FixIm.GetDimension())
    else:
        msg = "Transform must be either 'rigid', 'affine' or 'bspline'."
        raise Exception(msg)
    
    if Transform == 'bspline':
        LandmarkTx =sitk.LandmarkBasedTransformInitializer(transform=SitkTransform, 
                                                           fixedLandmarks=FixPts, 
                                                           movingLandmarks=MovPts,
                                                           referenceImage=FixIm,
                                                           numberOfControlPoints=NumControlPts)
    else:
        LandmarkTx = sitk.LandmarkBasedTransformInitializer(transform=SitkTransform, 
                                                           fixedLandmarks=FixPts, 
                                                           movingLandmarks=MovPts,
                                                           referenceImage=FixIm)

    return LandmarkTx

The above works fine for 'rigid' and 'affine', but the following error occurs for 'bspline':

Exception thrown in SimpleITK LandmarkBasedTransformInitializer: C:...\ITK\Modules\Core\Common\src\itkMultiThreader.cxx:395:
itk::ERROR: MultiThreader(0000025C4E20D020): Exception occurred during SingleMethodExecute

Any advice would be much appreciated.

[blowekamp]

Question addressed on ITK discourse: https://discourse.itk.org/t/using-landmarkbasedtransforminitializer-for-bspline-registrations/4096