Over the last several years, mobile mapping with an integrated LiDAR system has been quickly gaining ground as an accepted data collection method for transportation corridor projects. Major infrastructure planning and design firms as well as state transportation departments have touted benefits such as faster deliverables with increased data density and reduced risk with associated reductions in insurance costs. Mobile mapping appears to be well on its way to replacing other surveying technologies used in roadway design projects.
Such a blend often includes mobile LiDAR, terrestrial scanning, aerial photogrammetry and more traditional total station and GPS methods. Increasingly, it also includes stop-and-go scanning using a terrestrial laser scanner installed in a vehicle-based lift system, such as the TopoLIFT from Certainty3D. Securely fastened to a screw gear mechanism in a pickup truck-based bridge cradle, the scanner is automatically raised and lowered at each stop through computer-based controls in the truck cab to provide increased scanning efficiency and a safer operating environment compared to terrestrial scanning.
The crew is often able to move from setup to setup in less than 15 minutes--a significant reduction from the 90 minutes required with its previous terrestrial scanner. And if new scans are needed because of external factors such as vibration from a passing vehicle (which is also less likely to occur because of the increased stability of the system), the scans can be completed in just four minutes. “It’s an incredible productivity tool,” Kucza says.
Southeastern Surveying & Mapping began investigating the technology after handling several projects with mobile LiDAR. “On a recent urban project less than a mile long, we used stop-and-go scanning with the TopoLIFT,” Krick explains. “The TopoLIFT method provided rapid static scanning with redundant control points combined with on-the-fly scan stitching and inspection. This approach provided a high level of confidence in the data accuracy and coverage before leaving the project site.”
For all three firms, however, it’s not about the technology but rather the overall solution. “The biggest drawback of any scanning technology is the obscured area uncertainty and the questions revolving around how much terrestrial surveying will be required to complete the project,” explains Krick. “A thorough field review is essential and must involve the scanning professional, terrestrial surveyor and design professional to determine the realistic approach for project success.”
As LiDAR technology continues to advance, transportation projects will gain even more benefits. “The DOT survey deliverable in the near future will most certainly change,” Marino says. “LiDAR brings a solution that no conventional means can deliver on currently. The amount of quality data that can be collected and the efficiency with which it can be collected has to change the common deliverable. It will also change the way engineers work with project data. A true 3D design is not very far off.”