The technology is based on calculating the duration between an emitted laser signal and the reflected returned signal (time of flight scanner) or calculating phase difference between in the laser signal (phase based). Through advanced and precise movement of internal mirrors and servos, state-of-the-art LiDAR equipment can measure up one million unique points per second.
Time of flight laser scanners are typically used on long distances and precision is among other factors dependent on the accuracy of the internal clock that times the laser beam. Range accuracy for a long range LiDAR is typically within one centimeter. Time of flight lasers are ideal for measuring rock faces and snow covers at distances up to some kilometers.
Phase based laser scanners are used at shorter range and have in general a much higher precision than time-of-flight laser scanners. Phase based scanners are mostly used for mapping manmade structures like buildings and industrial installations.
NGI's state-of-the-art expertise
- Collection and processing of LiDAR data
- Georeferencing, draping and structural geology analyses of LiDAR-scan
- Temporal change detection of buildings and rockfaces
- Settlement detections
- Calculation of shotcrete thickness in tunnels
- Integration of LiDAR data in ArcGIS and CAD environments
Equipment at NGI
NGI conducts operational engineering work and research using two terrestrial LiDAR instruments: An long-range Optech ILRIS-LR and a short-range FARO Focus 3D.
The Optech ILRIS-LR scanner (as shown in the figure on top) is a long range time-of-flight based scanner capable of generating data at distances over 3 500 meters, however the speed of collection is limited to 10 000 points per second. This technology is ideally suited for slope monitoring and evaluation (specifically landslide, rockfall and snow avalanches). The scan below shows a mapped potential rockfall source and calculated volume of unstable masses.
The FARO Focus is a high-speed phase based scanner that collects data at a speed of 1 million points per second, the range of equipment is however limited to 120 meters. This technology is ideal for construction and tunneling environments (above to the right) where data collection time is limited and objects of interest are generally situated near accessible scanning locations. The FARO scanner is also ideal for measurements and analyses of deformations and cracks in buildings (above to the left).
The pictures below show the most dominant sets of planes present in a tunnel and thickness of applied shotcrete, both features calculated with the NGI-developed software PlaneDetect.
Relevant Equipment and Software
LiDAR related services
- Large scale landslide and rockfall mapping and monitoring
- Snow avalanche evaluation of failure area and path
- Volume calculation of:
- Failed masses
- Unstable masses
- Building deformation monitoring and calculations during construction and renovation
- Data collection and processing for drill and blast tunneling:
- Discontinuity measurements
- CAD vs. actual
- Tunnel progression
- Water leakage into the tunnel
- Distribution and spacing of rockbolts
- Shotcrete thickness mapping and evaluation