3D scanning offers solutions: modern surveying tools can also design.

• Author: Stricker, Julie
• Position: ENGINEERING

A long-delayed road construction project in Fairbanks finally looked like it was getting back on track this past September for PDC Inc. Engineers. The $50 million project would widen a 2.1 mile section of University Avenue, adding a 19-foot median and other safety improvements. It's one of Fairbanks' busiest roads, with more than twenty-one thousand vehicles traveling along it daily and a high accident rate, says Matt Stone, a civil engineer with PDC.

When engineers started looking at the data, however, they found some problems.

"This project is many, many years old," Stone says. "Some of the data was kind of patched together from many years of data collection. It all got kind of puzzle-pieced together. It was very outdated. There were a lot of features on the road that weren't actually shown on our topographical map."

A new survey was necessary, but time was of the essence. It was already late September and snow was forecast in the next few days.

A few years ago, this kind of project and deadline would have posed some pretty big obstacles for PDC Inc. Engineers, but technology offers a solution.

"A typical survey just wasn't going to be feasible," Stone says. "There would be safety issues with the surveyors on the road. It would probably have to be done at night. There were a lot of issues."

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Instead, the company opted to use a truck-mounted lidar scanner.

"It's pretty small but pretty expensive," Stone says. "But using this machine, we were able to drive that road at traffic speed. We had to drive it several times, but in the course of about two hours, we were able to collect the data we needed."

Measuring Distance with Light

Lidar is a survey technique that uses light to measure distance. The term is a combination of light and radar and is also an acronym for Light Detection and Ranging. Although lidar has been around for years, only in the past four or five years has it become a standard for airborne, ground, and mobile mapping applications, says Dennis Bogren, vice president and principal surveyor for PDC Inc.

"It's a very unobstructive and safe way of collecting large amounts of data," Bogren says.

Lidar sends out a swathe of laser signals that reflect off objects, similar to the way bats and dolphins use echolocation. The lasers measure every point in three dimensions, resulting in a cloud of data that can be used to create 3D model of a project and adjoining areas, Bogren says.

For the University Avenue...