[ITK] [ITK-users] Inverse of Versor Rigid Transform and RIRE

Mon Apr 6 22:24:08 EDT 2015

Hello everyone again, hope you are well!

I am use RIRE project, specifically  CT (movig) and MR_PD (fixed) images.
Basically, I hava a set of point (in millimeters) of the CT image to which
apply the trasform result of the registration and updaload this results in
the web for the evaluation. Example of set of points and his "ground truth"
:

Point      x          y          z        new_x       new_y       new_z

  1       0.0000     0.0000     0.0000   -7.5731    -41.2534    -27.3093
  2     333.9870     0.0000     0.0000  324.8722    -72.8159    -32.9063
  3       0.0000   333.9870     0.0000   24.1607    291.0393    -16.2727
  4     333.9870   333.9870     0.0000  356.6060    259.4768    -21.8697
  5       0.0000     0.0000   112.0000   -6.0554    -45.1157     84.6137
  6     333.9870     0.0000   112.0000  326.3899    -76.6782     79.0168
  7       0.0000   333.9870   112.0000   25.6784    287.1769     95.6503
  8     333.9870   333.9870   112.0000  358.1237    255.6145     90.0534 

So, the first I need is the transformation to apply, for that I do the
following : 

   //get the inverse transform
   TransformType::Pointer inverseTransform = TransformType::New();
   inverseTransform->SetCenter( finalTransform->GetCenter() );
   bool response = finalTransform->GetInverse(inverseTransform);

It makes sense to use the same center in the inverse transform?. A
"quaternion" define an "axis" (right part) of rotation and an angle to use
for rotate the image about this axis...why use a center of rotation...? 

Second, apply this transform...as follows: 

NewPoint = RotationMatrix * OriginalPoint + Offset

The rotation matrix and the offset are obtained from the inverse transforme
objetc. Found something wrong? something that is not taking into account ?
The results do not appear to be correct...the calculated error is too big
and does not correspond with the visual result.

Thanks in advance ...

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