The increased use of vehicle-based LiDAR mapping technology has led to the development of Mobile LiDAR systems that can collect a wide range of survey data to support a variety of transportation applications. Recent research has shown that certain parameters of interest (e.g. cross-slope data) can best be obtained through the utilization of mobile scanning devices rather than other technologies such as aerial LiDAR. Public awareness of Mobile LiDAR technology has been growing recently due to its wide-spread utilization to support street-level representations of road environments.
The American Society of Photogrammetry and Remote Sensing (ASPRS) has established a LiDAR Division with a primary focus on all aspects of kinematic laser scanning (e.g. the entire sensing platform is in motion). The division is comprised of two committees for Aerial and Mobile LiDAR and one working group on the LAS format. The Mobile LiDAR committee has been entrusted with the task of establishing best practices for Mobile LiDAR by soliciting inputs from the mobile laser scanning community, including service providers and academia.
To appropriately develop recommendations and guidelines for Mobile LiDAR usage, the committee has used the project life cycle approach along with the Work Breakdown Structure (WBS). The project lifecycle for a typical mobile LiDAR project consists of: 1) mission planning; 2) data acquisition; 3) LiDAR data processing; 4) product development; and 5) quality assurance/quality control (QA/QC) regimes.
The Work Breakdown Structure is a typical component of project management and system engineering processes. By following the WBS approach in the development of guidelines for Mobile LiDAR projects, every activity in the planning and production stages of a project, all project parameters, and all deliverables, must be considered. This can be a daunting task, indeed. With this mind, the committee has focused initially on some of the more critical project parameters to develop a base set of guidelines.
For mission planning, the guidelines address mobile LiDAR equipment standards, equipment calibration, GNSS control, PDOP, boresight calibration, and other related tasks. The guidelines also include recommendations for performing an inspection of the project area prior to data collection. The inspection will assist in determining the best time to collect data to ensure minimal artifacts in the LiDAR dataset from surrounding traffic or other factors and to identify obstructions that may cause GNSS signal loss.
The ASPRS guidelines also include recommendations for Geodetic Control, and address control point placement, point distribution and accuracy requirements for mobile LiDAR projects. While developing guidelines for geodetic control, the following elements were considered and addressed; transformation points used to constrain LiDAR data, check points to support QA/QC checks of the adjusted scan data, the utilization of either targeted control points, recognizable points (IDs) or coordinate positions within the scans, control points to support geometric correction or Spatial Constraint of the LiDAR data, and other processes.
The guidelines also recommend the use of data collection checklists to address three major categories: project materials needed before the mission, project materials needed after the mission and before vectoring, and project materials needed after vectoring.
Additionally, the guidelines suggest three types of validation of the mobile LiDAR data:
Swath-based accuracy validation
Check points-based approach
Cross section profile-based approach.
The validation of swath-based accuracy in aerial LiDAR has been examined by the aerial LiDAR committee and it is anticipated such an approach can be adopted for mobile LiDAR with limited or no modification. The swath-based approach addresses the geometric fit between the overlapping swaths in a single lift (or mission), geometric fit between the overlapping swaths in a project, and ultimately, between adjacent and overlapping projects.
The check point-based approach accounts for the different surfaces and the points to be collected in those surfaces. This is similar to FVA, SVA and CVA (fundamental, supplemental and consolidated vertical accuracy) parameters being used in aerial LiDAR. Additionally, the guidelines consider the practice of performing cross-section profile-based horizontal and vertical accuracy validation by comparing the profile data against the mobile LiDAR data. Any horizontal shifts in the data will be evident in the cross sections as an offset between the two data sets and can easily be measured and compared against project requirements.
The guidelines also address project deliverables, understanding that end products will vary from project to project.
In summary, the committee has made significant progress in developing a set of standard guidelines for Mobile LiDAR projects. However, there is much work to be done and opportunities for continued discussion and input will be available to those interested in participating in the process.