Survey teams lugging heavy equipment over terrain, taking readings every 50 or 100 feet or more: for decades, that was the only way of finding elevations and slopes. But no longer.
The last five years have seen an explosion in the use of lasers to do that work, according to Angela Livingston GISP, CP, CMS-Lidar, practice leader, geospatial services for Pape-Dawson Engineers, Inc.
Light detection and ranging (L iDAR) pulses millions of concentrated light beams per second to get a detailed picture of the ground. When each beam hits something solid, it bounces back and records that point’s location in three dimensions. Depending on the needs of the mission, the LiDAR sensor can be mounted on a drone that flies hundreds of feet above the ground, carried on a truck driving along a road or path, or operated by a crew that traverses the terrain on foot.
In the end, LiDAR helps engineers and architects understand the lay of the land. Is the area you’re building on flat? If it has rolling hills or drainage features, where and how prominent are they? How should the shape of the earth influence design?
So many data points
LiDAR is a game-changer in the sheer amount of detail it can provide: on average, a point every three inches, says Livingston. Contrast that with what ground crews get: readings every 25 feet, at most.
“A major benefit of LiDAR is that it can take the data and filter out the leaves, branches, and buildings to get to the bare earth,” she says. With so many data points, computer routines do much of the work automatically.
That doesn’t mean humans are out of the picture, she adds. After the computer analysis, “there’s still a manual process to make sure it ran right and clean up the model.” Pape-Dawson ground survey crews go on site to confirm data accuracy, too. Any reputable company will do that, but not everyone in the business does, she warns.
LiDAR not only records location data, but also the reflective intensity of the surface. This becomes especially useful when looking at signs or other reflective surfaces, as in a roadway mapping project in West Texas. By detecting the reflective intensity of roadway markings, LiDAR helped estimate how much paint to buy to keep the markings visible for drivers.
Quick work – in all environments
On average, LiDAR has made survey data collection 60-80% faster and cut costs in half, Livingston says. With the work she’s had to accomplish, “we would’ve had to hire hundreds of surveyors to do it. Some projects we did in a day, rather than the months it would’ve taken with people on the ground.”
Drone-mounted LiDAR can take readings in difficult or dangerous locations. Bridge decks, for example, may require millimeter-level readings taken up close. Drones can scan skyscrapers or other tall structures without endangering human pilots. Livingston has cooperated often with the company’s archeology group, too, scanning and photographing old foundations unearthed during construction with astounding accuracy.
LiDAR best practices
“We were one of the first surveying departments to use drones and LiDAR in Texas,” Livingston says. And that means she’s learned some important lessons since the advent of LiDAR surveying. Here are her tips.
- Check certifications. The American Society of Photogrammetry & Remote Sensing is the governing body for imaging and geospatial information. As both a certified photogrammetrist and certified LiDAR scientist, she recommends making sure your LiDAR experts are certified.
- Tailor to the project. LiDAR may not be the right solution in every case. It may be overkill for jobs when a survey team can accomplish the task in an hour or two using conventional methods, for example. “Each project has a custom solution,” she says.
- Use best technology when it counts. Where appropriate, the latest technology can get you the best results. Older scanners may sacrifice accuracy, for instance. She notes a new scanner gets almost twice the accuracy, and cleaner data. The laser characteristics mean it can also fly higher, which saves time overall.
Where does Livingston see this going in the future? “More and more people are adopting LiDAR, and it’s becoming everyday stuff.” In fact, new phones now feature LiDAR scanners, though they can’t collect the same data that an engineering team can. But as the technology improves, Livingston sees only great things in the future.
Pape-Dawson Engineers, Inc. has provided professional civil engineering consulting for water resources, transportation, environmental, surveying, GIS, and land development projects since 1965. With offices in San Antonio, Austin, Houston, Fort Worth, Dallas, and New Braunfels, Pape-Dawson is a leader in the civil engineering area, helping to strengthen communities throughout Texas.
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