Accurate Scale Factor Estimation in 3D Reconstruction

A well-known ambiguity in monocular structure from motion estimation is that 3D reconstruction is possible up to a similarity transformation, i.e. an isometry composed with isotropic scaling. To raise this ambiguity, it is commonly suggested to manually measure an absolute distance in the environment and then use it to scale a reconstruction accordingly. In practice, however, it is often the case that such a measurement cannot be performed with sufficient accuracy, compromising certain uses of a 3D reconstruction that require the acquisition of true Euclidean measurements. This paper studies three alternative techniques for obtaining estimates of the scale pertaining to a reconstruction and compares them experimentally with the aid of real and synthetic data.