 It is also possible to start with unprimed image coordinates and obtain primed 3D coordinates, which finally can be transformed into unprimed 3D coordinates.Again, in the ideal case the result should be equal to the above expressions, but in practice they may deviate.A final remark relates to the fact that if the essential matrix is determined from corresponding image coordinate, which often is the case when 3D points are determined in this way, the translation vector formula_25 is known only up to an unknown positive scaling.