Abstract. We analyze the noise sensitivity of the focal length computation, the principle point estimation, and the orthogonality enforcement for single-view 3-D reconstruction based on vanishing points and orthogonality. We first point out that due to the nonlinearity of the computation the standard optimal computation is not actually optimal. We then present a practical compromise between preventing the computational failure and maintaining the accuracy and demonstrate that our method can produce a consistent 3-D shape in the presence of however large noise. 1