By George Kopp, P.E., Missouri Department of Transportation (http://www.modot.mo.gov/), Jefferson City, Mo.
ollecting data to design Missouri Department of Transportation (MoDOT) projects can be time consuming and expensive. Traditional field data collection also can place employees dangerously close to traffic. However, light detection and ranging (LiDAR)-based mapping technology has emerged as a potential solution to field data collection problems.
MoDOT initiated a research project to evaluate the potential of LiDAR-based mobile mapping technology and other static 3-D scanning technologies for use in mobile, static and photogrammetric operations within the department. The main goal of the research was to evaluate advantages and disadvantages of data collected from LiDAR-based mapping technology compared with traditional photogrammetric and surveying methods.
Sanborn (www.sanborn.com) was hired to collect data using three different LiDAR data collection methods—static terrestrial LiDAR, mobile terrestrial LiDAR and airborne LiDAR—on a seven-mile MoDOT project on Franklin County’s Route A (see “Evaluating LiDAR Data Collection Options,” page 34). The project already had all the field control surveying and aerial photography collected using traditional survey methods. The project also had been mapped using traditional photogrammetric methods.
LiDAR surveying techniques offer numerous benefits related to safety enhancements, data quality for roadway design use, speed and cost.
LiDAR technology can provide a safer way to survey. Surveyors, motorists and designers will see an improvement in safety throughout the project corridor during surveying operations and through reduced site visits and design field checks. Aerial and mobile LiDAR reduces the need for surveyors on or near the road.
LiDAR surveys allow for more accurate development of project profiles and precise earthwork quantities. LiDAR data can be filtered from a detailed survey to a lower data density tailored to meet specific project needs.
Conventional aerial or LiDAR mapping provides for the shortest potential schedule for mapping data based on available staff and resources. The speed of data collection, especially with mobile LiDAR, can’t be matched via traditional methods. Such time savings allow surveying tasks to be completed within project constraints and scheduling.
Reducing the enormous amounts of data from the point clouds and processing the data proved to be the project’s biggest challenge, requiring the entire length of the contract to process and deliver the data in the required formats.
Conventional aerial mapping is still the most cost-effective way to collect mapping features, but LiDAR can provide potential cost savings by providing additional information content that may reduce field visits. LiDAR surveys can help reduce construction change orders in earthwork quantities by providing a more accurate existing ground model.
In addition, LiDAR data can help limit costs associated with design tasks by allowing existing sign surveys to be conducted from the office and assist in utility coordination by providing overhead clearances without having to conduct a separate field visit. The reduction of field work also saves user costs associated with traffic control and lane drops required to safely conduct field operations.
All three LiDAR technologies collect enormous amounts of point cloud data that proved challenging to process and manage with MoDOT’s current software, particularly the mobile dataset. The mobile technology significantly reduces field collection time but increases back-office processing, requiring potentially additional hardware and software to effectively manage the datasets.
One important issue in selecting a LiDAR technique is to evaluate the future multiple potential uses of the data. Although LiDAR surveys aren’t the best solution for all surveying needs, they do provide benefits to end users in terms of data and to the public in terms of reducing traffic disruptions during field work.
As a result of the Route A project and other LiDAR research during the last few years, MoDOT’s Design Division has taken several steps to implemen the technology:
• MoDOT purchased three static LiDAR scanners for evaluation in real-world project use. The units are from different vendors, Trimble and Leica Geosystems, and are being evaluated for cost effectiveness.
• MoDOT requested proposals for four aerial LiDAR surveys in its 2011 flight program for new or realigned roadways. These projects were a mix of urban and rural terrain and would have been done by traditional photogrammetric methods. Aerial photography also was obtained on these projects for quality control. For the 2012 program, MoDOT is requiring all aerial data to be collected with LiDAR technology.
• MoDOT is participating in and has a member on the panel for the National Cooperative Highway Research Program’s Project 15-44, Guidelines for the Use of Mobile LiDAR in Transportation Applications. The project is setting nationwide standards for the procurement, accuracy levels, and delivery methods of mobile LIDAR.
• MoDOT has a member on a Transportation Research Board Committee on Geospatial Data Acquisition Technologies in Design and Construction, AFB80. This group evaluates data acquisition technologies, such as LiDAR, and makes recommendations for methods and procedures in these areas.
• MoDOT is implementing design software that can make better use of LIDAR point clouds and large LIDAR models. This includes the use of 64-bit computing to provide adequate memory to
manipulate large datasets produced from LIDAR methods.
• MoDOT is seeking additional opportunities to implement LiDAR surveying techniques on projects while understanding that LiDAR may not be best suited for all surveying needs.
MoDOT is always on the lookout for technologies that allow it to provide services to the state of Missouri better, faster and cheaper. The agency’s LiDAR research and use indicates that, although
LiDAR has been on the emerging technology forefront for the last 10 years, the time for the technology’s cost-effective use has come. The agency’s LiDAR use will continue to increase as computer systems become faster and provide the ability to move larger amounts of data. The ability to find methods to streamline product delivery, decrease operation costs and improve employee safety always has been a high priority for MoDOT, and LiDAR is helping the agency meet those goals.