How can Lidar and inertial navigation systems be used for surveying?
Lidar data, by itself, has no reference to the real world. In order to make use of the Point Cloud, it is necessary to geo-reference the 3D lidar data using GPS and some type of inertial measurement sensor.
The Inertial Navigation Systems (INS) that are out on the market now combine the function of Real-Time Kinematic GPS along with inertial measurement. The inertial measurement works similarly to a person’s inner ear, it measures pitch, roll, and yaw as the sensor moves through the environment. The INS must be rigidly mounted to the lidar sensor. Along with the hardware considerations, there also must be a software data acquisition script and computing onboard to fuse the INS and lidar data. The script is usually coded in Python and its function is to write the data into a popular file format such as .LAS or .XYZ.
The marriage of the INS & lidar is critical to the overall accuracy performance of the system and is a unique to each mobile mapping system that is sold. Advanced integration techniques such as bore-sighting can be employed to hone accuracy even further. Velodyne has partnered with several leading lidar + INS integrators such as Lidar USA, Phoenix Lidar, and Paracosm.
Why is lidar more suitable for aerial surveying and mobile mapping than alternatives?
Lidar is most suitable in applications where the Z measurement, or height measurement of the subject area, is critical. Cameras and photogrammetry are great at imaging and measuring in X & Y direction, but struggle with the Z measurement of height. Additionally, 3D lidar can be superior to 2D Lidar because the individual lasers can hit at different angles of incidence. On traditional 2D lidar, the laser only hits at a direct 90 degrees, which also causes it to be susceptible to wind gusts creating gaps in the ground scan.
Why use lidar, rather than photogrammetry?
Lidar and photogrammetry are two different tools used for different scenarios. In more advanced integrations, both technologies can be fused together in order to create a colorized point cloud with XYZ & RGB data on each point. Lidar excels in applications such as power line maintenance where the Z height of the power line is a critical measurement. Photogrammetry and cameras would struggle in measuring the height of a power line from overhead.
What Velodyne products are most suitable for these activities?
Velodyne’s original HDL-32 is still the most accurate 3D lidar sensor available on the market today. With a range of 100m and accuracies down to 1.2cm on each of its 32 laser channels, the sensor is a great choice for the professional surveyor. The sensor takes in a huge swath of data, close to 1 million points per second, which reduces the time to complete large acreage surveying jobs. Velodyne also offers the economical VLP-16-LITE. At just 590 grams, it is a great choice for lighter weight and lower cost drones and UAVs. The extra-long range VLP-32 is also an option.
How can Lidar and mobile mapping assist with town/city asset management?
Lidar can be used to create a “digital twin” of the city. The digital twin is perfectly mirrored to the actual city, down to the centimeter, with billions of 3D data points. This digital twin can be used by virtually every public service such as the fire department, police department, department of transportation, city planning and construction, water, and countless other public and private organizations. The digital twin is the key to the smart city.
Case study – Utility Sector – Power Line Inspection for Electric Utility Companies.
The goal is to make sure the power lines are not too low to the ground, which could cause a spark and wildfire. Another goal is to make sure no trees or foliage are approaching the power lines. In previous years, inspectors would drive along long stretches of utility lines with an ATV and conduct visual inspections. This process usually required two to four people per team, with one being a dedicated driver. With lidar & INS, such as on the back of the ATV or on a drone, one single person can perform the inspection. The system also reduces the time for the inspection, which allows the inspector to cover more area at a faster rate. Human error and re-deploys are also drastically reduced by using lidar data. Similar use cases with massive productivity gains are forestry survey and infrastructure management. The United States Army Core of Engineers extensively uses Velodyne Lidar to scan dams and bridges.