3D Laser Scanning Services and the Use of Non-Contact Laser Scanners
There are two basic types of laser scanners: contact scanners and non-contact scanners. Contact scanners, as their name suggests, gather the spatial data of an object by physically probing it. In most cases, contact scanners are used in the manufacturing process to probe smaller objects for one of two purposes: to produce replicas of a certain object or to further refine the dimensions of an object that exists in model form. Non-contact laser scanners, on the other hand, do not probe their subject matter and are generally used to record the spatial data of larger objects, including buildings, building systems, sculptures, terrains and specific spaces. In most cases, companies and organizations that use non-contact laser scanning services to scan subjects like those mentioned above use either a time-of-flight 3D laser scanner or a triangulation 3D laser scanner, and sometimes use them in tandem. Below, we give an overview of time-of-flight and triangulation scanners along with their common benefits.
Time-of-flight scanners use a laser to probe their subject, which operates through the provision of a laser rangefinder. The rangefinder determines the distance between the scanner and the subject by measuring the round trip time of a pulse of light. The laser emits the pulse of light and the time between its emission and its reflection toward a detector is timed. Because the laser rangefinder only detects the distance of the single point within its direction of view, laser surveyors typically readjust time-of-light scanners multiple times when surveying the same object. Readjustments cab be made by either rotating the laser rangefinder or using a rotating mirrors system, with the latter being the most popular because it offers greater accuracy and can be done in less time. The greatest benefit of time-of-flight scanners is their ability to measure over long distances, making them the optimal choice for scanning the structure of buildings, large monuments and expansive terrains. However, when the surveying of buildings and large objects requires the scanning of minute details as well, laser scanning services providers often use triangulation scanners.
Like time-of-flight scanners, triangulation scanners use a laser to probe their subject. However, instead of using a detector to measure the reflection time of the laser, a triangulation scanner uses a camera to look for the location of the laser dot on the subject. The laser dot appears at different places in the camera’s field of view, depending on how far away it registers on a surface. Triangulation scanners receive their name because the camera, the laser emitter and the laser dot are arranged in a triangle formation. Both the distance between the laser emitter and the camera and the angle of the laser emitter corner are known, while the angle of the camera corner can be measured by observing the laser dot’s location within the camera’s field of view. These three measurements determine the triangle’s size and shape and identify the location of the triangle’s laser dot corner. Unlike time of flight scanners, triangulation scanners typically sweep a laser stripe across an object to speed up the data surveying process. An example of triangulation 3D laser imaging used to record the details of a larger object can be found in the 2005 3D laser surveying of the Plastico di Roma Antica by Gabriele Guidi, et al.