For people who think about buying a 3D laser scanner, there’s uncertainty about how exactly scanning works, how long scanning projects take, and how they can be calculated in terms of time and money.
Furthermore, professionals face the problem of having to calculate the personnel required not only for the scanning but also the subsequent data preparation (registration, modelling, etc.), a necessity that must be considered, especially when applying for construction projects or formulating offers.
For experienced users, it’s adequate to have 2D plans or photographs of the scan site. However, such plans are regularly lacking or it’s a mandatory step in the process.
How Does 3D Laser Scanning Work?
Scanners use a laser beam to measure the distance to an object point by point. The range depends on the model, FARO® Laser Scanners measure up to 350 meters. Modern scanners measure over one million points per second. A rotating mirror directs the beam in such a way that the objects (walls, pipes, etc.) are scanned vertically in rows. At the same time, the laser scanner rotates around its vertical axis. The next vertical row is close to the previous one. The result is an ASCII file with the polar coordinates (distance, vertical and horizontal angle) and the intensities of the measured points. The scanner is in the origin of the coordinate system.
Initially, ASCII files are not very meaningful. A software program is needed to visualize this raw data. These visualizations are similar to a 3D photograph that in former times resembled clouds due to the low density, elder laser scanners were working with. The corresponding FARO program is SCENE. But SCENE can do much more than just visualize 3D scan data. Besides numerous functions for processing scan data, SCENE also connects wirelessly to a FARO 3D Laser Scanner to control them.
Field of view of a laser scanner
A 3D scanner captures the parts of the scan site that it can reach with the emitted light beam. This includes the areas that you, as a user, will see when you stand on the scanner’s location and rotate around yourself. As an example, the scanner in the graphic above cannot capture neither the back side nor the two side surfaces of the small barrier. To completely capture the barrier and the space behind, at least two scans are necessary. The graphic below shows the situation in the top view.
Full coverage of the scan site using two laser scanners
Using two scanner positions the barrier is now completely captured. The shaded areas mark the space, the same-colored scanner can’t reach. The white areas are captured by both devices.
Registering Means Merging
One complete view of the room in one coordinate system is required. For this purpose, the scans must be merged and aligned against each other. The technical term for this is “registration”.
Analogous to how panorama images are made from individual overlapping photos, the scans are spatially aligned against the jointly captured areas. This is a so-called scan-to-scan registration. The result becomes more accurate when both scans are placed and captured with targets, which can then be detected and brought to congruence. Ideal three-dimensional targets are spheres with a well-known diameter.
Registering is a very time-consuming process and takes hours depending on the size and number of individual scans. It is prone to errors and usually done in the office. Since a project point cloud of the entire object can only be seen after the registration, missing parts or non-registerable scans are often noticed in the office. In this case, a renewed visit to the site is usually unavoidable.
FARO scanners connect wirelessly to a notebook using SCENE on a laptop to perform a full registration while scanning on site (on-site registration) both cloud-to-cloud and target-based registrations. This saves hours in the office and gives confidence that everything is captured what is needed.
Projects Must be Planned
To make a quotation for scanning a project, you need information about time and personnel required. For scanning usually only one person is needed. The number of scans, the suitable point densities and scan qualities must be defined.
The point density depends on the distance of the measured object from the scanner. As can be seen in the first graphic, the vertical lines on the barrier are closer to each other than on the wall. The resolution of the scanner must be chosen in such a way that the density of the measuring points corresponds to the specification of the measuring task. A point density that is too high considerably prolongs the scanning time and leads to unnecessarily large files. For accurate registrations the scans must have enough overlaps or must capture enough targets.
FARO ScanPlan – Perfect Tool for 3D Scan Project Planning
Using the FARO ScanPlan 2D mapper, floor plans can be captured at walking pace. Resulting 2D floor plans can be supplemented with 360° panoramic images and other factual data.
Additionally, the ScanPlan can assist in finding optimal positions for 3D scanners based on the recorded 2D floor plan. Depending on parameters, like point density and scan quality, it automatically calculates interesting scan project parameters such as the duration of individual scans as well as of the overall project.
Scanning a Villa
You may wonder how much effort is involved in scanning. As an example: The scanning of an old villa from the early 20th century. See here the resulting scan project:
The ScanPlan has calculated 20 scan locations after entering parameters for accuracy and point density. A single scan will take 4:35 minutes, the scan time for capturing the whole project is one hour and 32 minutes. The registration of the scans is done automatically and parallel to the scanning on site. No additional office time is needed after scanning. Below you find screenshots of the ScanPlan interface. The red dots in the plan correspond to the calculated scanner positions.
Everything is Scanned, What’s Coming Up Now?
The result of the scanning job is a point cloud project that can be viewed as a 3D image. First evaluations can be made in SCENE. By using FARO’s SCENE WebShare Cloud service the entire project can be made available to all project partners involved. In general, captured point clouds will be further evaluated. Usually, the reason for as-built capture is to include real geometries, such as buildings or industrial plants, in the planning of new buildings and conversions. Or to integrate them in BIM models, to monitor and manage buildings, structures as stockpiles and topographies.
FARO offers seamless Scan-to-CAD or Scan-to-BIM workflows, enabling the evaluation of point clouds directly in CAD and BIM planning tools such as AutoCAD, Plant 3D or Revit.