code: private void calcReferenceVector() {
  		referenceVector = getReferenceAxisCylic();
  
  		if (referenceVector == null) {
  			logger.warn("no reference vector found. Using y-axis.");
  			referenceVector = new Vector3d(Y_AXIS);
  		}
  		// make sure reference vector is perpendicular principal roation vector
  		referenceVector = orthogonalize(principalRotationVector, referenceVector);
  	}
docs: Returns a vector perpendicular to the principal rotation vector
  for the alignment of structures in the xy-plane
  @return reference vector