[Insight-developers] [GDCM] ITK Origin and coordinate system

[Mathieu Malaterre]

Bill,

	We are having a discussion with Gordon about a problem regarding the 
Origin of an itkImage read from a DICOM file. A while ago you put this 
code into itkGDCMImageIO(*). After discussion with Luis we came to the 
conclusion that the Origin is a fixed point. If you want to compute a 
point then yes you need to use the direction cosine and refer to the 
origin. But the origin should not change, right ?

Comments welcome,
Mathieu


(*)
   // DICOM specifies its origin in LPS coordinate, regardless of how
   // the data is acquired. itk's origin must be in the same
   // coordinate system as the data. This code transforms the DICOM
   // origin into the itk origin. The itk origin is computed by
   // multiplying the inverse(transpose) of the direction cosine times
   // the dicom origin.
   vnl_vector<double> itkOrigin(3), dicomOrigin(3);
   vnl_matrix<double> dicomDirection(3,3);
   dicomOrigin[0] = header.GetXOrigin();
   dicomOrigin[1] = header.GetYOrigin();
   dicomOrigin[2] = header.GetZOrigin();
   for (unsigned int ii = 0; ii < 3; ii++)
     {
     dicomDirection[0][ii] = rowDirection[ii];
     dicomDirection[1][ii] = columnDirection[ii];
     dicomDirection[2][ii] = sliceDirection[ii];
     }
   itkOrigin = dicomDirection * dicomOrigin;
   m_Origin[0] = itkOrigin[0];
   m_Origin[1] = itkOrigin[1];
   m_Origin[2] = itkOrigin[2];