The LiDAR Solution

Jan. 1, 2011
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As problem-solving and productivity-enhancing technologies for grading and excavating contractors continue to evolve, so does the interest in using them.

Lasers, total stations, GPS machine control, and 3D digital site maps have advanced to where they can collect and store data so that it can be used as tools by the contractor. Some contractors are now including another technology, LiDAR, as a valuable go-to addition to their technology toolbox.

LiDAR is the abbreviation for light detection and ranging. Developed in the 1960s, LiDAR itself is not new. Generally thought of as an airborne system, it allowed geologists, geographers, and other scientists the ability to capture terrain data while flying over remote or rough landscapes. Viewing the single laser images captured during LiDAR’s infancy is a bit like looking at a comic-strip-inspired Roy Lichtenstein pop-art painting, where the artist has zoomed in close, revealing the dot pattern of the newsprint character.

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As an optical remote-sensing technology, LiDAR measures properties of scattered light to find range and/or other information of a distant target by using laser pulses. It is similar to radar technology, which uses radio waves to measure the time delay between sending a pulse and detecting its reflected signal. The big difference is the size of what’s being beamed. Compared to radar, LiDAR uses much shorter wavelengths of the electromagnetic spectrum, typically in the ultraviolet, visible, or near-infrared range. Translation: smaller, more precise measuring is possible.

As a powerful data-gathering tool, LiDAR has found application in geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, remote sensing, and atmospheric physics. Add to that list… construction-site planning and management.

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With the more recent development of accurate inertial navigation systems and global positioning systems, current LiDAR systems are capable of high precision and accuracy. Lichtenstein’s dot pattern has been replaced by high-resolution digital photos.

Earlier LiDAR consisted of single laser pulses. Current LiDAR technology involves the rapid scanning of 10,000-15,000 pulses per second.

Not only has the technology itself advanced, but the concurrent development of GPS, GIS, computers, and software has led to systems that are now capable of extremely high precision and accuracy.

Airborne LiDAR has astounding applications that include detecting seismologic faults such as the Seattle fault line, measuring the uplift of Mt. St. Helens after its volcanic eruption, and for assessing damages caused by the earthquakes in Haiti and Chile.

And NASA uses LiDAR extensively to monitor glaciers and to perform coastal change analysis.

There are beneficial uses of airborne LiDAR for the construction contractor, who can capture the exacting details of a large or difficult job site, but this article will be limited to terrestrial LiDAR.

How Does It Work?
In elemental terms, a sensor sends out a pulse of light. “The light pulse travels out and hits an object, and some of the pulse is returned to the sensor,” states Randy Noland, vice president of marketing / business development and director of machine control, Carlson Software. “The time for that to happen is measured, multiplied by the time of light, and divided by two. For example, with Velodyne’s HDL-64E sensor, this happens 1.5 million times a second.”

Dave Hull, airborne imaging and LiDAR sales with Leica Geosystems Inc., elaborates: “LiDAR work like a reflectorless total station, but one that’s on steroids. The operator places it on a tripod, sets the scan parameters, and then pushes a “˜scan’ button. The instrument automatically rotates, scanning the surrounding terrain and site and collecting millions of closely spaced scan points of everything within its range in minutes. The operator then moves the instrument around the site as needed. Afterwards, software is used to stitch all of the scans together and to geo-reference them and, finally, to extract the needed terrain models and other data.”

Best Applications for the Earthmover
For earthmoving construction contractors, Hull offers three uses for terrestrial LiDAR: “The best applications of LiDAR in construction include (1) site planning and coordination; (2) earthworks quantities and quantitative analysis; and (3) accurate surface geometries for grading and staking.” Hull notes that there are many other construction applications of terrestrial laser scanning, but the others are more related to the structures being built than to the excavation and grading.

Jason Killpack, director of business development and strategic partnerships with Topcon elaborates: “LiDAR technology has several utilities when it comes to the construction process. Terrestrial-based stationary LiDAR scanners such as the Topcon GLS 1500 can measure an area before it is slated for new construction to create a digital terrain model or detailed topographic map. They can also be used to measure stockpiles and road cuts before and after material has been moved to generate volumetric calculations to better understand productivity and billing for the contractor. This technology utilizes the same setup methodology as traditional surveying equipment. It can provide digital photos and point clouds that are highly detailed for engineers and designers to utilize for future development.”

Killpack continues: “A new application for LiDAR technology comes from mobile mapping that utilizes LiDAR technology, GNSS, 360-degree digital camera arrays, inertial measurement units (IMUs), and precise wheel encoders to combine measurements to give the user a vehicle that can measure in high detail while driving at normal street speed. Called the IP-S2, our integrated positioning product can map large areas of raw land or streets at normal driving speeds with resolution of millions of points.”

Noland adds that high-definition scanners from Trimble, Leica, and Topcon employ LiDAR technology. “Those companies use static systems in the construction market for as-built and topographic surveys.” He points out that these scanners are good for areas where GPS is impaired, such as inside buildings, tunnels, or urban canyons. Noland continues: “These scanners are significantly faster than traditional GPS and, in many cases, more accurate because of the massive number of points taken. While the three major OEMs have static scanners, both Trimble and Topcon have mobile LiDAR scanner systems that are used in GIS. Eventually, these mobile systems will be adopted by the construction industry, especially with highway and other infrastructure projects that benefit from the ability to perform quick and accurate drive-by surveys.”

LiDAR Advantages
LiDAR offers capabilities that will not replace other technologies. It truly is another tool available to the construction contractor. “I view LiDAR as a supplement to GPS,” Noland says, “especially in GPS-denied environments.”

With the smaller image densities and the coherency provided by lasers, LiDAR provides construction contractors with some unique advantages. “More dense data provide more complete and accurate terrain models and quantities calculations that help save money and the schedule for a project,” states Hull. “More dense data can also improve site logistics, project coordination, and planning, while also reducing project costs and schedules.”

Killpack adds, “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.”

Continuing, Killpack states, “Current optical surveying systems are supplemented by terrestrial LiDAR. The field surveyor typically uses field experience to measure the defining features of the area to be surveyed. These measurements define the features that will be of the most interest to engineers, such as topology and geographical locations of infrastructure and utilities. With a terrestrial LiDAR system, millions of 3D points are measured that give much more detail of the area, versus selectively measured, less densely measured traditional surveys.”

Cost savings become apparent when compared with traditional measurement methods. Consider with LiDAR the amount of rich data, photo sets, and speed at which high-detail data are collected, as well as the ability to perform mapping over large distance. The speed and cost savings can be significant.

“LiDAR provides much faster results and subsequently shorter project cycle times,” Noland states. “A contractor often only needs 10 minutes to scan an entire room, or a job site in 30 minutes. This makes the collect process safer, since there is less time onsite, which can mean less distraction to the crew on the site. Additionally, the point clouds easily transfer into office software.”

Investment Cost
LiDAR system costs vary and depend upon configuration and laser scanner type. Look to invest anywhere from $85,000 to $300,000. (Unfortunately, even though the high-end LiDAR will likely do everything you need, it still won’t walk the dog.)

The Future
Digital job files are not new; the depth and detail of the files created by LIDAR technology are. Therefore, it raises what Noland calls “a deep and interesting question”-Where is LiDAR technology heading, and how soon will we get there?

“The market for the use of LiDAR technology for site planning, grading, and excavation is barely penetrated and headed toward much greater adoption as the word gets out to the industry about its productivity, cost, quality, and schedule benefits,” states Hull. He admits that the adoption curve is steep and contractors are still learning about the technology, its uses, and benefits.

“The LIDAR marketplace will continue to grow as the technology becomes more robust and the speed of computers and application software improves to handle the amount of data that is collected,” Killpack concludes. “The ability of the hardware systems to deliver rich, detailed data sets will drive innovation of the engineering and construction industries to adopt and utilize these new tools in the best ways that they see fit. Seeing a picture of the job site that can be measured in innumerable ways is a value that will continue to increase to the consumers of job-site data and all that it conveys.”