Transportation infrastructure of all kinds—from an ordinary-looking sidewalk or bike lane to a highway flyover, from an efficient intersection to a gasp-inspiring bridge—begins at the same place: understanding the site.
Decades ago, surveyors in the field painstakingly recorded angles, elevations, and other data, then brought it back to the office for engineers to work from. Nowadays, laser scanning technology, known as LiDAR, has supercharged the surveying world, speeding up timelines and recording survey grade meta-data information. But that LiDAR technology continues to rely on survey crews who walk the terrain. “Every project still uses surveying methodology,” says Tom Ruschkewicz, RPLS, PLS, Senior Vice President, Survey/Geomatics. “We need them to geo-reference the sensor-collected data to real-world coordinate values.”
“Surveyors paint the roadside black-and-white chevrons, crosses, or checkerboards that let us accurately use LiDAR,” adds Angela Livingston, CP, CMS-LIDAR, Vice President and Geospatial Practice Leader. Surveyors might also need to take readings where scanners can’t go or identify aspects scanners cannot. “An operator might need to open a manhole cover and get information about what’s underneath and determine engineering conflicts that may need resolution,” explains Tom.
Surveyors augment their data-collection capabilities with advanced geospatial technology, such as:
Aerial LiDAR. Scanners flown on airplanes or helicopters are perfect for long, linear routes. “We can capture 20 miles in a few hours, rather than days or weeks with a survey crew,” says Tom. The higher the scanner is off the ground, the less detailed the picture it captures, but aerial LiDAR’s can capture 50 or more survey grade data points per meter (PPM), providing a high level of detail that engineers need about the terrain.
Mobile LiDAR. Truck-mounted scanners are slower than aerial platforms, but they get better definition because they travel just above the surface. “You get more data points the lower to the ground you go,” says Angela, “and the mobile LiDAR can get about 5,000 PPM.” It can also pick up details aerial LiDAR misses, such as surface utilities, signage, etc. Another benefit: sensors take data from all around the vehicle, including above it, which planes cannot do. Though it may only map 60 miles in a day (depending on road width, traffic, and other factors), it can scan through tunnels or under bridges and overpasses.
Terrestrial LiDAR. Survey crews can operate tripod-mounted scanners to fill in other methods’ gaps. “LiDAR is a line-of-sight technology,” Tom reminds, “so whatever the scanner on the mobile or aerial platform misses a static sensor on the ground needs to pick up.” Not simply a supplemental data source, the terrestrial scanner is the go-to solution for some areas. Setting it up in the four corners of an intersection can map the surroundings while keeping people and equipment safely out of traffic, for example. It also fits the bill when FAA restrictions prohibit aerial platforms or drones.
Drone-mounted LiDAR. Drones help where safety or environmental considerations prohibit humans or other vehicles from scanning, say under bridges or at high elevations. A new addition to Pape-Dawson’s collection specializes in tight spaces, providing a new capability for data collection.
Body-mounted LiDAR. For congested areas, Pape-Dawson’s body-mounted NavVis scanner can take readings quickly and easily. Faster than terrestrial LiDAR collection, it comes in handy in walkable spaces inside buildings, under overpasses or bridges, as well as with sidewalks and traffic intersections.
“We have a collection of tools at our disposal,” Tom says, and each tool in Pape-Dawson’s kit has its use. “We won’t use survey crews when it’s unsafe, of course,” and scanners win out on fidelity and speed: “A scanner can get 5,000 data points per meter, where a survey crew is lucky to get one point per meter…and the scanner can do it in a fraction of the time.” Still, people remain essential to the process. Angela sums up the approach: “Every project is different, and we look for the best way to use the tools together.”
The geospatial team combines the data, constructing a point cloud that approximates the site’s terrain and structures. From that, they produce deliverables to be used by the engineers for their design work. Engineers receive 2D and 3D drawings, as well as a triangulated surface that shows the terrain, viewable in geographic information system (GIS) or computer-aided design (CAD) software (including Civil 3D and Revit). From that essential starting point, the engineering work can commence, knowing the design rests on a firm foundation: a detailed understanding of the site.