ScanPhase

Distance measurement:

Laser scanning systems primarily record the precise spatial location of a target object, constructing a point cloud composed of points in Cartesian coordinates (XYZ). This is accomplished through the comparison of emitted and returned light pulses, allowing for the determination of the target object's position relative to the scanning instrument.

The scanner computes the object's position by measuring the angle of the scanner assembly, comprised of the scanner head and reflector, along with assessing the travel time of light. This time measurement can be direct, as in the case of flight time scanners, or indirect, as observed in light-based scanners utilizing phase measurements.

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Color and intensity:

The laser scanner also records a measure of the return energy (represented as an intensity value) from the surface, which is a function of the characteristics of the target surface and ambient light conditions. Most scanners have the ability to determine the color of each point by using a camera (can be incorporated or separated), which is represented by the scale of values ​​RGB (red, green, blue) commonly used. Because scanners are optical systems, only what the scanner can "see" is captured, so laser scanners can not go through walls or other obstacles (these create "shadows" in the cloud of points where data is not captured) . In fact, the integrity of the data depends on the environmental conditions during the acquisition, as well as the intensity and color data, which vary according to the lighting conditions.

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Point clouds:

The measurement data is encoded using a file format that delineates the position, intensity, and color of individual points within the point cloud. Ultimately, this data can be stored in diverse point cloud file formats (e.g., ASCII, PTS, LAS, E57), each employing variations in the XYZ / RGB position, intensity, and color scheme.

Numerous hardware and software providers offer proprietary point cloud formats that can be easily converted to meet the customer's specific requirements. It's advisable for customers to articulate the desired deliverable file formats based on the intended data usage during negotiations with service providers. This becomes especially crucial when integrating the data with pre-existing information management systems.

Customers may find it beneficial to opt for a standard, non-proprietary file format, like the ASTM E57 format for exchanging 3D image data, to ensure alignment with the project's specific needs.

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Accuracy of the measurement

Several factors affect the accuracy of the point cloud data, including instrument capabilities and calibration, and quality control measures. Environmental conditions that affect the integrity of the data include the reflectivity of the surface, the angle between the scanner and the target (angle of incidence), and the range to the target object (the laser beam diverges with distance, so the measurements furthest from the instrument are less precise). 3D scanning service providers are experts in controlling these sources of error, so it is crucial to establish functional performance requirements before field acquisition so that the optimal instrument, the scanning position (s) and the Acquisition times can be negotiated with the service provider to achieve the highest quality deliverables. However, a series of general rules that customers must know to ensure the proper development of functional performance requirements are applied.

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Mobile / aerial systems:

The mobile and aerial scanning systems, where the scanner is mounted on a moving vehicle during the measurement process, capture additional data about the movement of the vehicle to compensate for the movement. A global navigation satellite system (GNSS) detects the position and speed of the scanner, an inertial measurement unit (IMU) detects the attitude speed and acceleration of the scanner. This information is stored and processed during the data acquisition process, and then the processing. The software generates a point cloud file with the adjusted physical positions, which allows the project teams to capture data very quickly from the physical environment without having that mobilize the team several times. Additional data, such as environmental conditions during the data capture time, as well as calibration and service provider data, may also be linked to the data set. Aerial and mobile scanning is fast becoming the standard method for creating digital city models, documenting road networks, tunnels or power lines, and other infrastructure measurement initiatives.