High resolution laser radar for 3D imaging in artwork cataloguing, reproduction and restoration

摘要

A high resolution Amplitude Modulated Laser Radar (AM-LR) sensor has recently been developed, aimed at accurately reconstructing 3D digital models of real targets, either single objects or complex scenes. The sensor sounding beam can be swept linearly across the object or circularly around it, by placing the object on a controlled rotating platform, enabling to obtain respectively linear and cylindrical range maps. Both amplitude and phase shift of the modulating wave of back-scattered light are collected and processed, providing respectively a shade-free, high resolution, photographic-like picture and accurate range data in the form of a range image. The resolution of range measurements depends mainly on the laser modulation frequency, provided that the power of the backscattered light reaching the detector is at least a few nW (current best performances are ～100 μm). The complete object surface can be reconstructed from the sampled points by using specifically developed software tools. The system has been successfully applied to scan different types of real surfaces (stone, wood, alloys, bones), with relevant applications in different fields, ranging from industrial machining to medical diagnostics, to vision in hostile environments. Examples of artwork reconstructed models (pottery, marble statues) are presented and the relevance of this technology for reverse engineering applied to cultural heritage conservation and restoration are discussed. Final 3D models can be passed to numeric control machines for rapid-prototyping, exported in standard formats for CAD/CAM purposes and made available on the Internet by adopting a virtual museum paradigm, thus possibly enabling specialists to perform remote inspections on high resolution digital reproductions of hardly accessible masterpieces.