How to augment the second image? Recovery of the translation scale in image to image registration

In this paper, we present an automatic pose estimation (6 DoF) technique to augment images using keyframes pre-registered to a CAD model. State of the art techniques recover the essential matrix (5 DoF) in an automatic manner, but include a manual step to align the image with the CAD reference system because the essential matrix does not provide the scale of the translation. We propose using planar structures to recover this scale automatically and to offer immediate augmentation. These techniques have been implemented in our augmented reality software. Qualitative tests are performed in an industrial environment.