This chapter discusses the strengths and weaknesses of techniques of 3D laser imaging based on time of flight and triangulation. Laser scanning by triangulation is a fully developed technology. Through this method, it is now possible to create faithful 3D datasets from a reasonable range of surface materials. However, laser scanning has some certain drawbacks, restricting their universal applicability. For surfaces with concavities or with intricate details, occlusion may occur due to the necessary separation of the viewpoint between the viewing camera and the laser projector. In addition, the data may be corrupted by false and poor returns caused by variable material reflectance. In the time of flight system, the distance is measured by measuring the time for a focused laser beam to impact on and return from the surface of interest. In this method, the distance is computed and a 3D image can be created if the laser beam is scanned across the target. Although, the time of flight method is a more attractive alternative as it eliminates occlusion, it has disadvantages as well. The time resolution necessary to measure the range to sub-millimetre accuracy is difficult to achieve and the measured time is also affected by the magnitude of the returned signal. In addition to reviewing the pros and cons of this current technology, the chapter also discusses the development of a new approach to time-of-flight laser imaging based on time-correlated single photon counting. This new method has various advantages compared to the old methods. It has the ability to make 3D measurements on distance, poorly reflecting or transparent surfaces.
Three-Dimensional Imaging via Time-Correlated Single-Photon Counting
