Introduction to LiDAR¶
Active remote sensing with visible or near-infrared lasers to measure distances
Can be mounted on tripods, cars, planes, helicopters, drones, satellites, and more
How do LiDAR systems measure distance?¶
Three primary methods:
By measuring the time-of-flight of laser pulses.
By measuring the time-of-flight of single photons.
By using interferometry to count the fractional number of wavelengths between a scanner and a target.
How is LiDAR used?¶
Terrestrial Laser Scanning (TLS)
Mobile Laser Scanning (MLS)
Airborne Laser Scanning (ALS): also called Airborne Laser Swath Mapping (ALSM)
Unmanned Laser Scanning (ULS)
Discrete vs. full-waveform¶
Outgoing pulses are not instantaneous — they have a finite width and height (approximated by a Gaussian)
Return energy is not instantaneous either (see picture)
The “full waveform” output (see picture) is usually simplified down to single points (discrete-return)
Georeferencing¶
LiDAR data is usually only useful if placed in a larger project or global context.
“Registering” LiDAR data to a global coordinate system is called georeferencing.
Georeferencing static (TLS) scans is usually done via known control points, either benchmarks or GNSS survey points.
Georeferencing mobile or airborne (MLS/TLS) scans is done by combining LiDAR data with position and orientation information from a GNSS/IMU mounted alongside the LiDAR scanner.
How is LiDAR processed?¶
Vendor-specific software (e.g. RiSCAN PRO and RiPROCESS, from RIEGL)
Other commercial softwares (e.g. TerraStation, QT Modeler)
Mixed-source software (e.g. LASTools)
Open-source software (e.g. CloudCompare, PDAL, laspy)
Next¶
On to Introduction to PDAL