Laser scanners may seem to do the same job - more or less - but they are different. They excel in different environments and useages. This document limits itself to talking about Terrestrial Laser scanners as these are the main type used when recording refineries, process/chemical plant and most other assets. Laser scanners fall into two catagories "Time of flight" and "Phase based"
As its name suggests a time of flight scanner measures the time it takes for a pulse of light to travel from a laser source - to the target and then the return journey to the receiver that is locate as closely as posible to the laser source. The speed of light is constant so the variations in accuracy are down to the devices ability to time the flight. There is also a lot of co-ordination to go on as each point is gathered and the laser beam is redirected and a sequential process records the data
A phase based scanner uses a constant beam of light emitted at a fixed frequency. the device calculates the distance to the target by looking at the phase shift in the returned signal. this method is a lot quicker than the Time of flight scanner but its range and accuracy are not as good.
The two types; Phased Based and Time of flight, excel in different enviroments. The time of flight with its long range and accuracy make it an ideal tool for building facads, cliffs, large open structures with large exposed faces. The phase based scanner is better at intimate spaces like building interiors, and the more complex the more advantageuos the phase based is, with their short range and high speed they are ideal for multiple scans around equipment. When a time flight machine is used in an intimate environment like a piperack in a refinery its advantages start to count against it. The longer scan time increase costs and the long range starts to increase the noise on remote surfaces (if the point data is viewed in a unified database)
The differences between the two can be seen in the data. the higher accuracy and lower set up rate of the time of flight tends to give a "cleaner" scan data. the noiseband on surfaces tends to be smaller and the points appear more regular. The Phase Based scanner when used correctly will give much more information and tends to have better penetration into spaces due mainly to its ease of use and consequent increase in scanning locations. this also tends to reduce shadows etc on complex plant and other cluttered environments. It does tend to be more "fuzzy" with noise bands of surfaces being thicker than that of the time of flight data. .
So which one? The big players like Leica geosystems Faro and Z+F all have excellent products. Leica is associated with the time of flight philosophy whilst Z+F and Faro are associated more with Phase based scanners. you need to speak to them to find out !!