Leica Geosystems' product family not only includes powerful and versatile time-of-flight laser scanners such as the Leica ScanStation C10 and the ultra-high speed Leica ScanStation P20 but also features the HDS8810 mine scanning system. This portfolio of products becomes complete with Leica Cyclone, Leica CloudWorx and Leica TruView software, providing a full set of Leica-quality geo-referencing, surveying, and CAD integrated engineering tools for creating accurate deliverables and working with large scan data sets with unparalleled ease.

High-Definition Surveying not only offers many benefits to the measurement professional, but also to the recipients and users of accurate spatial informatin. Civil engineers, plant designers, CAD professionals, architects, contractors, forensic investigators, archaeologists, and owner/operators can all reap the cost and added-value benefits that HDS provides.

HDS systems can provide significant cost savings in many ways:
- Lower cost as-built & topographic surveys
- Reduction or elimination of costly "return visits" to the site
- More accurate, complete as-builts for retrofit design projects translate into better retrofit designs. These translate, in turn, into (1) less construction rework due to interferences and fit-up problems and (2) the ability to  factory-fabricate instead of field-fabricate.
- Reduced facility downtime due to (1)fast, unobtrusive scene capture and/or (2) minimal field fit-up, field fabrication, and field rework thanks to accurate as-builts.
How does Laser Scanning work?
Time of Flight
The simplest way to think about “time of flight” laser scanning is to look approach it as nothing more than a laser range finder.  I think we all understand how a laser range finder works.  It basically measures a distance by shooting a laser beam out to an object and measuring how long it takes that laser beam to bounce back.  By knowing the speed of light (laser beam) and measuring the time, I think we can all figure out that the distance is computed by multiplying the time divided by two and multiplying it by the constant for the speed of light.  Anyone that understands surveying realizes that to compute an x,y,z position, you need to know the distance to the object, the bearing (horizontal angle from a known line) to the object and the vertical angle (angle from gravity) to the object.

Therefore a time of flight scanner does nothing more than measure the distance and horizontal and vertical angle for every position it is at. This is accomplished by the scanner moving in a grid fashion in a 360° horizontal plane and approximately 330° vertical plane.  This is why “time of flight” scanning is substantially slower than “phase based” scanning.  The scanner head must actually occupy all of the grid positions for each x,y,z position.  Time of flight scanning has been known for longer range, but a slower acquisition time.  Acquisition speed has always hovered right around 50,000 points per second, but with a range of 300 meters.  Just recently a million points per second “time of flight” scanner was brought to market, but the range is only 120 meters.  More in line with the phase based scanners.  However the range was decreased to 120 meters, down from 300+ meters.   It will be interesting to see which technology wins out, “time of flight” or “phased based”.

Phase Based
Phase based scanning utilizes a constant beam of laser energy that is emitted from the scanner.  The scanner then measures the phase shift of the returning laser energy to calculate distances.  Everything else is the same as the “time of flight” scanner. Phase based scanners can acquire data at a rate upwards of a million points per second.  However their range is limited to around 80 meters. Phase based scanners are mostly suited for Industrial plant work and building interiors.
Source : http://floridalaserscanning.com/3d-laser-scanning/