3D-Registration

Using a three-dimensional point set requires the registration to be changed so that it contains a three-dimensional transform, optimizer, and image. I first tried to use the itkRigid3DTransform but found that it was also a base class for more specific transforms. itkVersorRigid3DTransform was one of the transforms derived from itkRigid3DTransform and allowed rotation along with translation. The transform had its own tailored optimizer called itkVersorRigid3DTransformOptimizer that would work over the six parameter in the transform. After inserting the optimizer and transform into the registration process I needed to change all the instances of point sets in the registration and visualization into three-dimension ones. The initial parameters in the transform and the scales in the optimizer needed to be augmented to take into account there now being six parameters.

Once the registration was up and running I started to play around with different coordinates to see whether it was working properly. I started by enabling just translation in the x and y-direction by scaling out all the other parameters. Thus the registration was basically two-dimensional over a slice of the three-dimensional image. But the metric value remained extremely small. Throughout the extant of the process there were not any drastic or significant changes. This could be the result of the image not being read correctly into ITK or the point set being in the incorrect position relative to the image.