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.
But appearances don’t always tell the whole story. According to the survey managers responsible for choosing the most appropriate technology for every project, the latest state-of-the-art doesn’t necessarily translate to the best approach--at least, not independently. “All site conditions must be considered, from safety on high-speed interstates to highly obscured rural corridors,” says Gary Krick, PSM, president of Southeastern Surveying and Mapping Corp., headquartered in Orlando, Fla., a firm that has been involved with a number of transportation-related projects. “Although modern technologies provide the transportation design community with more tools to choose from, none of these technologies is the complete solution. They require the right professionals to determine how to blend the technologies in an approach that will lead to project success.”
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.
When Milwaukee, Wis.-based consulting engineering firm Kapur & Associates was looking to replace its older-model terrestrial scanner, the firm considered mobile LiDAR but wanted more flexibility than what an integrated mobile system would provide. According to Daniel Kucza, PLS, survey manager, the Riegl VZ-400 terrestrial laser scanner offered impressive accuracy and scan speeds; when used with a TopoLIFT, the system greatly increased the survey crew’s productivity. “The VZ-400 is a very fast scanner, and the TopoLIFT is a very fast way to collect data,” he says. “Looking at the substantial cost of a mobile machine, and the cost of mobilizing it to the site, I thought static with the TopoLIFT was a really good fit as a stepping stone in between static LiDAR and mobile.”
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.”
Bartlett & West, a multidisciplinary firm headquartered in Topeka, Kan., also has a Riegl VZ-400 terrestrial scanner with a TopoLIFT in its tool set. For projects that can be driven, “the TopoLIFT allows us to be more efficient than just the tripod method,” says Survey Manager Steve Marino, PLS.
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.”
Such an approach often involves the use of multiple technologies. “We have several partners that allow us to bring a mobile solution as well as an aerial solution,” says Bartlett & West’s Marino. “Each technology has helped us create a wider range of solutions for our clients.”
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.”
The full value of such services will have a long-term impact. “What we’re doing with scanners is bringing contractors and owners more information than they ever thought they would have use for, and we’re making it useful to them,” says Kapur & Associates’ Kucza. “With this information, we’re lowering their risk factor and allowing them to make more competitive bids, which increases the efficiency of infrastructure projects overall.”