Calculating RMSE in Landmarks Registration

domP · November 3, 2022, 10:45am

Hi,
Could I ask if anyone has a code to calculate RMSE obtained from “Fiducial Registration Wizard” module?
I have read the repository’s code linked below:

github.com

SlicerIGT/SlicerIGT/blob/master/FiducialRegistrationWizard/Logic/vtkSlicerFiducialRegistrationWizardLogic.cxx#L480


      
          //------------------------------------------------------------------------------
          double vtkSlicerFiducialRegistrationWizardLogic::CalculateRegistrationError(vtkPoints* fromPoints, vtkPoints* toPoints, vtkAbstractTransform* transform)
          {
            // Transform the from points
            vtkSmartPointer<vtkPoints> transformedFromPoints = vtkSmartPointer<vtkPoints>::New();
            transform->TransformPoints(fromPoints, transformedFromPoints);
          
          
  // Calculate the RMS distance between the to points and the transformed from points
            double sumSquaredError = 0;
            for (int i = 0; i < toPoints->GetNumberOfPoints(); i++)
            {
              double currentToPoint[3] = { 0, 0, 0 };
              toPoints->GetPoint(i, currentToPoint);
              double currentTransformedFromPoint[3] = { 0, 0, 0 };
              transformedFromPoints->GetPoint(i, currentTransformedFromPoint);
          
          
    sumSquaredError += vtkMath::Distance2BetweenPoints(currentToPoint, currentTransformedFromPoint);
            }
          
          
  return sqrt(sumSquaredError / toPoints->GetNumberOfPoints());
          }

but when I have tried to replicate it on Matlab I have got the wrong result.

Below my data and results:
Fixed points: [61.8616132503630; 48.4552443635927; 42.4899670291801]
[29.4899390311330; 48.4552443635927; 23.5335812251265]
[77.9016320076391; 48.4552443635927; 35.1990494122364]

Moving points transformed: [61.9137516947608; 48.4552459716797; 43.5304726392767]
[27.5809622469604; 48.4552459716797; 22.7209879790148]
[79.7584735999537; 48.4552459716797; 34.9711363721714]

RMSE from Slicer: 1.7214
RMSE from Matlab: 0.8654

Fixed and moving points are expressed in RAS coordinates.

Below my Matlab code:

euclideanDistance= zeros(3,1);
for i= 1:3
euclideanDistance(i)= ((norm(points_moving{i} - points_fixed{i})));
end
RMSE= sqrt(mean(euclideanDistance));

lassoan · November 3, 2022, 3:56pm

You need compute the mean of the error^2 (vtkMath::Distance2BetweenPoints provides distance^2). In your matlab code you computed the mean of error instead.

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Calculating RMSE in Landmarks Registration

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