The components that make Mobile LiDAR Mapping a reality – Ken Shipley PLS
New technology and recent advancements in the Mobile LiDAR Mapping arena now provide survey, mapping and GIS professionals a rapid method of data collection from a moving vehicle.
To understand this new technology I will review six components that contribute to the process of three dimensional data collection. A Topcon IP-S2 system is illustrated below for reference.
Global Navigation Satellite System (GNSS) Positioning
Standard generic term for global satellite navigation systems that provides autonomous geo-spatial positioning with global coverage. GNSS allows small electronic receivers to determine location (longitude, latitude, and altitude) within a few meters using time signals transmitted along a line-of-sight by radio from satellites. Receivers on the ground with a fixed position can also be used to calculate the precise time and position to centimeter level accuracy.
Inertial Measurement Unit (IMU)
The IMU measures and reports on the vehicles velocity and orientation and is instrumental in supplying correction values for acceleration and rotation of the vehicle. The IMU uses a combination of accelerometers and gyroscopes and are typically used to maneuver aircraft, including UAVs. This sophisticated electronic component has been primarily developed for missile and unmanned aerial system guidance for the military.
Light Detection and Ranging (LiDAR) Sensors
The LiDAR sensors measure laser light returns to determine line of sight distances at a rapid rate. The result is a dense cloud of points with XYZ coordinate values. By using the constant speed of light, the time difference between the emission and the reflection can be converted into a slant range distance (line-of-sight distance). With an accurate position and orientation of the sensor provided by GNSS and IMU data, the XYZ coordinate of the reflective surface can be calculated.
Vehicle Data Bus (CAN-bus) and Wheel Encoders
The CAN-bus is a high-integrity serial data communications bus for real-time control applications and can operate at data rates of up to 1 Mega bits per second. The CAN-bus has excellent error detection and confinement capabilities and was originally developed for use in cars. They are now being used in many other industrial automation and control applications.
Wheel Encoders are the preferred method for vehicle tracking during GNSS outages and allow one to measure the precise speed or distance a wheel travels. With wheel encoders it is possible to determine the direction of movement and provide information for odometry (use of data from the movement of actuators to estimate change in position over time). Vehicle direction can be determined by implementing two line detectors with two tracks and a set phase.
360 Degree Camera
The following specifications are for the Ladybug3 manufactured by Point Grey: Embedded JPEG compression engine800Mbit/s IEEE-1394b (FireWire) interface, 12 MP images at 15 FPS, Six (6) progressive scan color CCDs.
The Receiver/Recorder provides processing, logging and time-stamping of sensor data to provide real-time, fused feedback. The logged data file may also be post-processed and filtered offline to provide improved position information and geo-registration of sensor data.
Also see - GIS Data Collection with Topcon IP-S2