Laser Scanner Is a Model Helper for Construction Engineers

Daniel C. McCarthy

The redesign of a building generally requires engineers to make a three-dimensional "as-built" microstation model of the structure before they can even begin creating a scale representation. Traditionally, this process requires a combination of close-range photogrammetry and hand-drawn sketches captured by a team of designers encamped for weeks at the site. In the redesign of a Detroit power plant, however, a small team from Raytheon Engineers & Constructors finished the job in half the time with the help of a laser scanning system from Cyra Technologies.

Detroit Edison, an electric utility in southeastern Michigan, hired Raytheon to help improve compliance with US regulations on nitrogen oxide emission at the utility's Monroe power plant. One potential solution entails constructing a reactor where the original plant designers hadn't intended to build anything. Steel supports, ductwork, piping and everything else associated with the new process would need to be installed in, around and through existing equipment.

Conventional as-built modeling requires field data to be correlated and manually digitized later off-site. The process relies on human interpretation and carries the potential for design errors that can snowball once construction begins. "The motivation for using three-dimensional as-built modeling on a project is the potential for savings [during] construction," said Greg Lawes, manager of advanced technology for Raytheon Engineers. "Projects, such as power plants, that have a lot of piping previously may have required 5 to 6 percent of the data to be reworked; laser scanning reduces that to less than 1 percent."

Survey-grade, three-dimensional points produced by Cyra's laser scanner quickly provided accurate as-built modeling data for the interior of Detroit Edison's Monroe power plant. Courtesy of Raytheon Engineers & Constructors.

Cyra's Cyrax laser-scanning system measures reflected light from a portable, Class II pulsed green laser to collect 500,000 survey-grade three-dimensional points from natural surfaces up to 100 m away without the need for targets. Data collected still require post-processing to extract features from the point clouds. Because less than 1 percent of the data obtained with the system must be reworked, however, scanning can significantly reduce the potential for human error. And it provides more possibilities for automating the process. "The significant time spent on the as-built phase of a project is in modeling," said Lawes.

Cyrax's scanner package does not come cheap, at a cost of more than $170,000 for the scanner, power pack, laptop, software and training. But Lawes said: "Anything you miss in the design phase becomes much more expensive in construction. It's not the cost per day to rent the unit, it's the cost of not doing things right the first time."