Cheap photogrammetry versus expensive reverse engineering techniques in 3d model acquisition and shape reconstruction

This paper aims at verifying a procedure both for the acquisition and the reconstruction of 3D CAD models by combining Photogrammetry and Reverse Engineering techniques. This procedure makes use of a passive optical system and a photogrammetry-based software. Reverse Engineering techniques allow to get the digital duplication of a real object starting from a point cloud acquired with a 3D scanner from a point cloud by means of CMM (Coordinates Measure Machine) or optical systems. The use of CMM can ensure result very accurate (≈ 1µm), but shows two drawbacks: 1) the digitizing phase is very slow, and due to the high number of points a powerful (fast) computer is needed, 2) the high cost of the CMM. Today, optical systems, like laser scanner 3D, are often used in RE applications. They allow to realize very fast acquisition with an acceptable smaller accuracy. Optical systems though less expensive than CMM, remains however too expensive. For this, the main target of the authors is to search a cheaper acquisition and 3D reconstruction process to get good results similar to results obtainable by means of common RE systems. The Photogrammetry methods allow to get the dimensions and the shape of a real object by means of three or more photos. In the literature there are very few studies on the applications of photogrammetry in industrial field, especially in the acquisition of small size parts of mechanical components. So, the innovative aspect of this paper is the analysis of the results obtainable in industrial applications (close-range photogrammetry of small components) by using cheaper technological resources, like a digital camera, and a software based on photogrammetry. This work moves along four steps: first there is a view of the photogrammetry and its applications, the system used and the analysis of a particular case study are presented. Last, results and conclusions on the procedure used are outlined.