Active 3d Sensing * Active 3d Sensing for Heritage Applications

Permission is granted to quote short excerpts and to reproduce figures and tables from this report, provided that the source of such material is fully acknowledged. Abstract Active three-dimensional vision is concerned with extracting information from the geometry and the texture of the visible surfaces in a scene, reasoning about the data and finally, communicating the results. In order to take full advantage of these vision systems, one must understand not only their advantages but also their limitations. This paper covers some issues that must be addressed before embarking in a 3D scanning project. 1 Introduction In the last twenty years, many advances have been made in the field of solid-state electronics, photonics, computer vision and computer graphics. Non-contact three-dimensional (3D) measurement techniques like those based on structured light and passive stereo are examples of fields that have benefited from all of these developments (Handbook 1999). These non-contact measurement techniques have found widespread use in heritage, environment modeling, virtual reality, and many industrial fields. Figure 1 shows a classification of non-contact measurement strategies that rely on light waves. In the case of passive techniques (that use ambient light), only visible features with discernable texture gradients like on intensity edges are measured. Laser-based systems are used to structure the environment in order to acquire dense range maps from visible surfaces that are rather featureless to the naked eye or a video camera. Hence, the 3D information becomes relatively insensitive to background illumination and surface texture. This paper reviews the basic principles that underline the majority of