Euclidean 3D reconstruction from stereo sequences with variable focal lengths

Abstract

A stereo rig can be calibrated using a calibration grid, but recent work demonstrated the possibility of auto-calibration. There remain two important limitations, however. First, the focal lengths of the cameras should remain fixed, thereby excluding zooming or focusing. Second, the stereo rig must not purely translate, which however is the most natural type of motion. This also implies that these methods collapse when the motion comes close to being a translation. The paper extends the literature to allow changes in focal lengths (these may be independent for both cameras) and purely translational motions of the stereo rig. First, the principal points of both cameras are retrieved. Changes in focal lengths are then dealt with through weak calibration. Each position of the rig yields a projective reconstruction. The projective transformation between them allows to first retrieve affine structure which subsequently is upgraded to metric structure, following the general outline described in [12]. Rather than posing a problem to the method, rig translation allows further simplifications and is advantageous for robustness.