LiDAR for Your Toolbox?

Nov. 1, 2012

I’m a sucker for thingamajigs, so here I am waxing poetic over a technology that has been around for more than half a century, but whose brightest days may lie in the future. I first came in contact with LiDAR 35 years ago while working on the Air Force’s MX missile project, and I’ve been intrigued by its possibilities ever since-possibilities, I might add, that have come about more through advances in computer capabilities and data storage capacity than fundamental changes in the technology itself.

LiDAR stands for “light detection and ranging,” a technology able to create an interactive topographic map by scanning the earth with lasers. It is similar to sonar in that it measures distance by the time it takes for the laser to reach the ground and bounce back to the source. While laser scanning is routinely done from fixed locations, vehicles and aircraft are being used more and more frequently to increase coverage. In addition to job-site surveys, LiDAR is useful in planning for corridor projects such as road construction but can assist in overall project management as well.

Who knows better than you the significant time and effort you have to devote to keeping track of where things are on the site and monitoring the status of construction activity? The upshot of this, as again you are well aware, it that the timely knowledge of project status-where things are, what has been done, what needs to be done-is among the most vexing issues facing construction managers today. OK, you say, but is there a way to accomplish this without affecting the workflow or breaking the bank?

The emergence of scanning lasers has made real-time updates and earthwork calculations a valuable adjunct to worksite management, particularly so because data gathering is nonintrusive and does not impede the construction progress. After collection, the scanned data are imported and then processed to provide a constant update allowing

  • real-time assessment of construction progress;
  • remote monitoring of construction by design engineers, project managers, architects, etc.;
  • early detection of errors in construction procedure, resulting in cost savings;
  • obtaining as-built models of terrain and structures; and
  • improved project planning and documentation.

Recent experience shows that calculation of cut-and-fill requirements can be done pretty much on the fly, while 3D graphical renderings of the terrain can be accomplished using any of several commercially available software packages.

Why LiDAR in earthmoving projects?

Earthmoving construction applications of LiDAR include site planning and coordination; rapid access to earthworks quantities, and analysis; and development of accurate grading surface geometries. For general construction purposes, there are many other construction applications for terrestrial laser scanning related to below- and aboveground structures. Moreover, high-definition systems from Trimble, Leica, and Topcon employ LiDAR technology for use in such GPS-impaired areas as inside buildings, tunnels, or urban canyons.

Before construction begins, terrestrial-based stationary LiDAR scanners can measure an area to create a digital terrain model or detailed topographic map. They can also be used to generate volumetric calculations of stockpiles and road cuts before and after construction to estimate and then validate quantities for billing. Laser scanners are subject to much the same setup techniques as traditional surveying equipment, but in addition to site location assignments, they can provide detailed digital photos and point clouds for future activities.

The primary advantage to the construction contractor is to get much more detailed data about a site or structure versus traditional measurement data supplied by optical measuring devices such as total stations.

LiDAR has been used in fixed-base applications for quite some time, but today we’re seeing a fusion of LiDAR technology, GNSS, 360-degree digital camera arrays, inertial measurement units, and precise wheel encoders that allow vehicular deployment of mobile systems capable of highly detailed measurements at normal street speeds.

The place where cost savings become really apparent is when you compare the wealth of rich data, the addition of photo sets, and the speed of collection with traditional surveying and mapping systems outputs. This is particularly true where the ability to perform mapping operations over large distances is concerned.

So is there LiDAR in your future? Maybe, maybe not, but whichever direction you intend to go, it will be well worth your time and trouble to let the providers show you what’s on the shelf and in the works.