The basic principle of 3D scanning is to use a 3D scanner to collect data about a subject. The subject can be:
- an object
- an environment (such as a room or even a landscape)
- a person (3D body scanning)
Some 3D scanners can simultaneously collect shape and color data. A 3D scanned color surface is called a texture.
3D scans are compatible with Computer-Aided Design (CAD) software and also 3D printing, after preparing the 3D model via specific software. A 3D scan can give a lot of information about the design of an object, in a process called reverse engineering.
3D scanners are powerful tools for professionals in several industries, such as automotive, aerospace, dental, and jewelry, as well as in more artistic applications such as video games, special effects, and animation movies. 3D scanning technologies rely on different physical principles and can be classified into the following categories:
- Laser triangulation: Projects a laser beam onto a surface and measures the deformation of the laser ray.
- Structured light: Measures the deformation of a light pattern when projected onto a surface to 3D scan the shape of the surface.
- Photogrammetry: Also called “3D scan from photographs”, this technology reconstructs a subject in 3D from 2D captures (photos) with computer vision and computational geometry algorithms.
- Contact-based 3D scanning technology: Relies on the sampling of several points on a surface, measured by a mechanical, optical, or physical probe.
- Laser pulse: Based on the Time of Flight (ToF) of a laser beam. The laser beam is projected onto a surface and recollected by a sensor. The time of travel of the laser between its emission and reception gives the surface’s geometrical information to the 3D scanner.
3D scanning technologies
Laser triangulation 3D scanning technology
Laser triangulation-based 3D scanners use either a laser line or a single laser point to scan across an object. First, the 3D scanner casts its laser onto the object. As the laser light reflects off of the 3D scanned object, its initial trajectory is modified and picked up by a sensor.
Then, based on this modified trajectory and thanks to trigonometric triangulation, the system can detect the laser’s deviation angle. The calculated angle is directly linked to the distance from the object to the scanner. When the 3D scanner collects enough distances, it is capable of mapping the object’s surface to recreate it in 3D.
The main advantages of the laser triangulation technology for 3D scanning are its high resolution and accuracy.
One downside to laser triangulation technology is how sensitive it is to the properties of object’s surface; very shiny and/or transparent and/or dark surfaces are particularly problematic.
Structured light 3D scanning technology
Structured light 3D scanners use trigonometric triangulation but do not rely on a laser. Instead, they project a series of linear patterns onto the object. The system is then able to examine the edges of each line in the pattern and how the lines are deformed and to calculate the distance from the scanner to the object’s surface.
The projected structured light used for 3D scanning can be white or blue and generated by numerous types of projectors, such as Digital Light Processing (DLP) technology. The projected pattern is usually a series of light rays but can also be a randomized dot matrix.
The main advantages of structured light technology for 3D scanning are its speed and resolution, and its non-harmful light can be used for 3D body scanning.
However, structured light 3D scanners are sensitive to lighting conditions and have trouble working outdoors in broad daylight.
Photogrammetry 3D scanning technology (photography)
Photogrammetry is the science of making measurements from photographs, especially for recovering the exact positions of surface points. Photogrammetry is based on a mix of computer vision and powerful computational geometry algorithms.
The principle of photogrammetry is to analyze several photographs of a static subject, taken from different viewpoints, and to automatically detect pixels corresponding to a unique physical point.
This 3D scanning technology’s main challenge is to examine tens or hundreds of photos and thousands of points with high accuracy. To run such photogrammetry algorithms, a very powerful computer is required.
The main advantages of photogrammetry 3D scanning technology are its acquisition speed and ability to pick up colors and textures. Photogrammetric technology is also capable of reconstructing subjects at large scales, such as landscapes or monuments photographed from the ground or from the air, by a photography drone, for example.
The quality of the results generated by photogrammetry technology is dependent on the resolution of the input photographs. This technology can also be quite slow, depending on your software and PC setup.
Contact-based 3D scanning technology
Contact-based 3D scanning is also known as digitizing. This 3D scanning technology implies a contact-based form of 3D data collection.
Contact 3D scanners probe the subject via physical touch, while the object is firmly held in place. A touching probe is moved along the surface to record 3D information. The probe is sometimes attached to an articulated arm capable of collecting all its respective configurations and angles for more precision.
Some specific configurations of contact-based 3D scanners are called Coordinate Measuring Machines (CMM).
Contact 3D scanning is widely used to perform quality control after fabrication or during maintenance operations. The main advantages of the contact technology for 3D scanning are its precision and ability to 3D scan transparent or reflective surfaces.
The downsides of contact 3D scanning technology include its slow speed and inability to work with organic, freeform shapes.
Laser pulse-based 3D scanning technology
Laser pulse-based 3D scanners, also known as Time-of-Flight scanners or Lidar laser 3D scanners, measure how long a casted laser takes to hit an object and come back.
Since the speed of light is exactly known, the time it takes for the laser to come all the way back gives the exact distance between the 3D scanner and the object. In order to precisely measure the distance, the 3D scanner computes millions of laser pulses with accuracy up to the picosecond (1 picosecond equals 0.000000000001 seconds!).
Since each measure only collects one point, the 3D scanner needs to cast its laser 360 degrees around that point. To do so, the 3D scanner is usually fitted with a mirror that changes the orientation of the laser.
Time-of-Flight 3D scanners encompass both laser pulse and phase shift lasers. Phase shift laser 3D scanners are a sub-category of laser pulse 3D scanners. In addition to pulsing the laser, phase shift systems also modulate the power of the laser beam. Phase shift lasers offer better overall performance.
The main advantage of laser pulse 3D scanners is their ability to 3D scan very big objects and environments. They are, however, quite slow.
Laser pulse technology is often used by terrestrial laser 3D scanners, which are mainly destined for land surveying or to 3D scan entire buildings. Some laser pulse 3D scanners also incorporate dynamic SLAM algorithms to enhance their ability to recognize their surroundings.