Stereo-camera calibration for large-scale DIC measurements with active phase targets and planar mirrors

We propose an easy-to-implement yet accurate calibration method for large-scale 3D measurements that makes use of a regular-sized phase target and two planar mirrors. Being insensitive to severe defocus, the phase target is placed as to span a large depth within the field of view (FOV) of each camera for accurate intrinsic calibration. Extrinsic calibration is achieved by placing the phase target in the FOV of a short-range virtual stereo-system generated by the mirrors. Results from 3D shape and deformation measurements demonstrate that the proposed method is capable to operate within a working volume of 3 m × 2 m × 1.8 m with an error < 0.1% of the FOV thus opening to new possibilities for large-scale measurements in mechanical and civil engineering applications.