From a given position vis-à-vis the object to be digitized, the scanner projects a low-power, non-damaging laser light upon a section of the object’s surface. Each point of the surface touched by the laser light is captured by a CCD camera integrated into the scanner, and both the X, Y, Z coordinates and the laser light intensity of each of these points are recorded in the memory of the computer controlling the scanner. This operation is repeated thousands of times each second and generates a file containing a large amount of point data of the scanned surface. This file, displayed on the computer screen, shows the 3D shape of the scanned surface.
Thus, the operation of creating sequential overlapping images from multiple points of view on the surface of the object is carried out until the entire surface of the object is covered. Individual 3D digital images thus captured are then aligned together with appropriate software using overlapping sections of the images to create an accurate 3D digital model of the object. The software makes it possible to eliminate redundant points in overlapping sections in order to generate a homogenous density of 3D points throughout the model.
Some scanners capture the color directly with laser scanning - in this case, RGB values (Red, Green, Blue) are recorded along with the X, Y, Z coordinates - or indirectly by mapping a color photograph taken while scanning the 3D digital image. In the latter case, lighting conditions will have an effect on color quality.
Here, the term ’’object’’ refers to small, medium and large objects (ranging from a few millimeters to a few meters in length and width) as well as buildings and large sites (ranging from many square meters to a few square kilometers in surface area). According to the object or site to be scanned, the 3D scanning process is carried out by moving the object in front of the scanner or by moving the equipment around the object or inside and around the site.
Today, we can find a wide range of 3D scanning systems available on the market. The following main characteristics differentiate these systems:
- Operating mode;
- Capacity to capture a given color;
- Accuracy of measurement;
- Resolution (planar resolution and depth resolution);
- Need to install or not control targets in the scene to be digitized;
- Portability; and
- Operation range (distance between the scanner and the surface to be scanned).
While operating methods with a 3D scanner are typically quite similar, we will not use the same 3D scanning system to digitize a small statue, the interior or exterior of a building, or a human body. The choice of the right system is dictated by the needs and specifications of the project itself. Thus, a single system will not be suitable for all types of projects.