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Laser Scanning

Laser scanning is used when high detail and high precision is required. It can pick up extremely small features and when paired with photogrammetry can create a nearly perfect 1:1 virtual replica of the subject.

The only downside is that most laser systems are very expensive; the lowest starts around $2,000 and the next lowest is $20,000.

There are a couple different kinds of laser scanners, depending on their use case.

Time of Flight (LiDAR)

This system is great for long ranges, scanning outdoors or situations where a powerful computer is not available, like in a cell phone. An emitter on the device sends out pulses of light which hit the scanning subject and return back to a sensor.

The computer calculates the difference in time that it takes for each laser pulse to return to the sensor. If it hits a point further away from the camera it will take slightly longer to return to the sensor than a laser pulse that hits a nearer object. This difference in the time it takes for the laser to “fly away” and then “fly back” is how a 3D point cloud is constructed.

Phase Shift Laser Scanning

With this method the scanner emits a constant laser beam in multiple phases. When they hit an object their phase will change and based on the difference between the different phases the scanner can determine depth and distance.

It is a very accurate, versatile and fast way of scanning a wide range of objects from very small to very large.

Structured Light

Structured light scanning can be done with lasers or visible light.

These scanners project a known pattern of light on a scene. For example, using a single line or a pattern of dots.

In the case of the latter; dots that get smaller are determined to be further away and dots that get larger are closer to the camera. The scanner takes a picture of this distorted pattern and compares it against other pictures with other distortions and from that builds a 3D scan.

It is very inexpensive, is very fast and does not require a very powerful computer compared to photogrammetry. However most systems can’t be used outdoors or in areas with infrared lights as they will interfere with the structured light pattern.

Microsoft Kinect for the Xbox 360 is a structured light scanner.
Image by Audrey Penven.
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