Laser scanning

Laser scanning is a 3D scanning method in which the surface of an object is captured with a laser beam or laser line and the position of points is determined by triangulation or by measuring distance. The term covers two distinct groups of devices: scanners for machine parts and machines, and long-range scanners for factory halls, buildings and terrain.

Triangulation scanners project one or more laser lines onto the surface, and a camera views them from a known angle. This group includes handheld scanners, laser probes on portable measuring arms and scanners mounted on robots or coordinate measuring machines. Handheld scanners with a blue laser and a few to several dozen crossing lines determine their position from reference targets stuck onto the object, or are tracked by an external optical system. Typical accuracy is around 0.02 to 0.05 mm and degrades by roughly a few hundredths of a millimeter per meter of object size.

Long-range scanners (LiDAR), whether terrestrial on a tripod, mobile or carried by a drone, measure distance from the time of flight or the phase shift of the reflected beam. From a single station, a rotating head captures the surroundings within a range of tens to hundreds of meters in a few minutes. Point accuracy is typically in millimeters, and in centimeters for mobile and airborne systems. The result is a point cloud of an entire hall or building, often in the E57 format.

Compared with structured light scanning, a laser is less sensitive to ambient light and copes better with dark and shiny surfaces. On small parts with fine details, however, a stationary structured light scanner tends to be more accurate.

A handheld laser scanner suits medium-sized to large parts and assemblies (frames, car bodies, molds, machine beds, piping, ship propellers) and scanning on site, where the part cannot be shipped or removed. On objects several meters in size, it is combined with photogrammetry to maintain overall accuracy.

Long-range laser scanners capture the as-built condition of factory halls, production lines, process piping and buildings, for example as a basis for fitting a new machine, rebuilding a line or creating a building information model (BIM). They also pick up features that are easy to miss when measuring by hand, such as pipes, cable trays or beams, and reduce the risk of clashes during installation.

Reference targets are stuck directly onto the part. Small, intricate parts may have no room for them, and adhesive residue can remain after they are peeled off. Sharp edges, sheet metal edges and small holes often come out rounded or inaccurate in the data, so critical features are best measured additionally with a touch probe. Match the resolution to the purpose: a fine resolution slows scanning down and inflates the data volume.

The accuracy of long-range scanners does not meet the requirements for checking machine part tolerances; their data serves for layout planning and documentation. For hall surveys, make sure the individual stations are tied together through control points and that the provider states the registration accuracy achieved.

Ask what volumetric accuracy the provider guarantees for your object size, whether they will use photogrammetry, and in which coordinate system and format they will deliver the data.