Container integrity verification using laser triangulation

We present a system for verifying the integrity of storage containers using a laser triangulation scanner, with applications in nuclear security. Any intrusion into the container shell and subsequent reconstruction of the surface inevitably leaves slight changes to the three-dimensional surface structure which the proposed system can detect. The setup consists of a laser line scanner, mounted on a rotation stage. We propose an auto-calibration procedure for this system which − from several scans of a planar calibration target acquired from different viewpoints − automatically determines the position and orientation of the rotation axis with respect to the scanner coordinate frame. We further present an algorithm for the automatic registration of two 3D scans of a cylindrical surface, not requiring any user interaction such as the identification of corresponding point pairs. We show that the algorithm accurately aligns two scans of the same object, acquired from different viewpoints. The accuracy of the overall system is dominated by the measurement uncertainty of the 3D scanner; residual errors resulting from the calibration and registration are subordinate. The system can reliably detect changes in the surface shape resulting from tampering.