code: public double getProjectedDistance(Atom point) {
  		Atom projected = getProjectedPoint(point);
  		if( projected == null) {
  			// translation only
  			return Double.NaN;
  		}
  
  
  		return Calc.getDistance(point, projected);
  
  	}
docs: Get the distance from a point to the axis of rotation
  @param point
  @return The distance to the axis, or NaN if the RotationAxis is purely translational