Short range scanners:
3D scanners with laser triangulation
Laser triangulation scanners use either a laser line or a laser point to scan an object. The sensor captures the laser light, which is reflected from the object, and using a trigonometric triangulation system calculates the distance from the object to the scanner.
The distance between the source and the laser sensor is well known, as is the angle between the laser and the sensor. When the laser light is reflected from the scanned object, the system detects the angle at which the light returns to the sensor, thereby calculating the distance from the source of the laser rays to the surface of the object.
Pros and Cons:
+ Available in various forms, they are often more portable, require less training and are less sensitive to ambient light.
– Generally less accurate, lower resolution and make more noise.
Scanners with structured light (white or blue)
Structured light scanners also use trigonometric triangulation, but instead of capturing laser light, these systems create linear patterns on an object. Then, noting the end of each line in the pattern, they calculate the distance between the scanner and the surface of the object. Basically, instead of the camera looking at the laser lines, it sees the ends of the projected grid and calculates the distance in the same way.
Pros and Cons:
+ They are usually accurate with high resolution and less noise.
– They are limited by scanning space, generally bulky and sensitive to surfaces (preparation required).
Medium and long-range scanners (focal distance over 2m):
Laser pulse 3D scanners
Laser pulse scanners (also known as "time-of-flight" scanners, the time it takes the laser to get from the source to the object) are based on a very simple principle: since the speed of light is absolute, if we know how long it takes for the laser beam to reach the object and is reflected back to the sensor, then we know how far away the object is. Pulsed laser systems use cycles accurate to the picosecond (or one trillionth of a second) to measure the time it takes for millions of laser pulses to return to the sensor, thereby calculating the distance. As the laser and sensor rotate (often via a mirror), the scanner can scan 360 degrees around itself.
Pros and cons:
+ Medium and long range (2 - 1000m).
– Less accurate, slower data collection, more noise.
Laser phase-shifting 3D scanners
Phase-shifted laser systems are another type of "time-of-flight" scanner technology, and the concept of operation is the same as that of pulsed lasers. In addition to laser pulses, these systems vary the power of the laser and the scanners compare the phase of the laser that was sent and then returned to the sensor. This measurement is very precise.
Pros and Cons:
+ More precise, collect data faster and are less noisy.
– Medium range only
Photogrammetry
Photogrammetry is basically the science of measurement using photography. The starting material in photogrammetry can be the most ordinary map, measurements or a 3D model of a real object or location. Many of the maps we use today were created with the help of photogrammetry and photographs taken from airplanes. Photogrammetry can be classified according to different parameters, such as one standard method based on the location of the camera at the time of photography. Based on this we have sector photogrammetry and close range photogrammetry.
Computed tomography
Computed tomography is a method by which, with the help of computer processing, we obtain a three-dimensional image by taking multiple X-ray images of an object from different angles. The study is carried out in successive sections.
Markers (Trackers)
These measuring systems are mainly used for scanning large objects by tracking the position of the measuring device in relation to the object and recording any changes. Markers can be contact or non-contact and can use various types of measuring devices.