Geo Week News

September 11, 2008

Oregon tests mobile scanning

This just in. On September 17th, a few days after we published this story, Terrapoint announced that David Evans and Associates had purchased a TITAN mobile scanning system.

In July, the Northwest Region, Region 2 of the Oregon Department of Transportation (ODOT)commissioned David Evans & Associates Inc. (DEA) to collect roadway characteristics on about 70 miles. The data will assist the state agency with a widening project of Highway I-5, as well as various preservation projects that include improving the safety of guardrails and the widths of lane shoulders, updating sidewalks to meet ADA requirements and other related measures.

According to Marcus Reedy, DEA’s director of survey & mapping, such work used to be completed with a measuring wheel to obtain lineal feet of guiderail and a collection of various notes on the conditions of the guiderails with data provided via spreadsheets. Cross slopes were determined by placing a level at various mile posts at sections of pavement. This rudimentary data-collection procedure led designers on an extraction chase of great manual effort.

“Most of their designers now are working with MicroStation and InRoads,” Reedy says, “so they are typically doing all their design work in CAD. But when surveyors come back with spreadsheet data, you can see the gap there. Big gap.”

ODOT—via DEA—turned to mobile scanning. This budding technological technique allowed for rapid data collection for a variety of mass data types that exceeded the accuracy requirements ODOT sought. And, according to Reedy, data collection didn’t need to be increased or decreased depending on the requests of the designer using this method. Whether data was needed on striping, guardrails or on sidewalks, “You don’t have to ramp it up and down. You get it all,” he says.

Plus, data can now be extracted at any point requested and put into a requested CAD format.

DEA used the TITAN system by Terrapoint. Reedy says the company’s survey division views the point density of the point clouds as “outstanding. We’re still amazed with the accuracies that we’re getting compared to traditional survey shots (digital levels, RTK shots, terrestrial laser scanning). It’s consistently impressive.” Point density and accuracy (to design level) were prominent factors in the decision to purchase the TITAN system—which the company later did—along with the requirement that data was model-able (able to be put into a CAD program), collected at a rapid rate and provided safety benefits.

“Safety is huge for us,” Reedy says. “I’ve told our surveyors (200-plus surveyors across the company), [that]there is no need for us to put our surveyors on mainline freeways for that type of data collection. We’ve done terrestrial laser scanning for eight to nine years now. [Now] we’re able to drive along with the flow of traffic and collect the data just as well as we would with a tripod setup.“

DEA doesn’t have an analyzed percent to report regarding safety impacts from mobile scanning, but he knows it reduces field exposure time and provides fewer distractions for travelers.

Other benefits? Certainly a response to the ecological responsibility many companies are taking these days. “As a company, we’ve said that we’re going to decrease our carbon footprint by 10 percent in 2009,” Reedy says. “Mobile scanning will be one of the factors to reduce our carbon footprint.“

Enhancement to jobs is another benefit. “Mobile laser scanning isn’t going to replace the other technologies (i.e., static scanning)—it’s going to enhance [it],” Reedy says. As an example, Reedy describes the collection of data on an overpass for design purposes—replacement or widening.

Collection would still take place using static scanning versus mobile scanning, he says, because “[for]that type of accuracy, we would be using the wrong tool for the expected outcome.” Where it would enhance the project, he says, is if the client needed data on a mile of roadway on each side of the structure for a profile. “It’s good enough for the bridge clearances for a preliminary analysis, but final design will require traditional survey methods.”

This perspective is enhancing DEA’s project roster, Reedy says. “We’re surveying things that we would never survey before just because it was too expensive. Competing technologies (low-flying aerial photography and helicopter LiDAR for corridor mapping) obviously have benefits [by not having]the restrictions of the roadway. But, they’re also very expensive to mobilize. [Mobile scanning] is fairly inexpensive to mobilize. You also don’t have the environmental restrictions other than rain. For us, the economic benefit is that it’s new business. We won’t be doing traditional static scanning along 10 miles of highway anymore. But we also wouldn’t have gotten 70 miles of highway [work]if we didn’t have access to this.”

But what about the drawbacks of this emerging technology?

“[There’s] lots of training,” Reedy says. “You’re dealing with quite a few software packages to get the accuracy and be sure all your data is up to specification. There’s a rigorous QC process that you go through.” And, he says, the office processing tasks require at least a week to understand on a preliminary level—and that is someone who is already familiar with GPS procedures.

Technology itself—specifically, navigation system technology—is a frequent obstacle to mobile scanning. Sketchy or bad GPS windows don’t fare well in the collection process. So, those working in cities and urban and forested areas need to carefully plan for such impediments to work flow.

Another prerequisite of mobile scanning is the pre-mission planning efforts. GPS mission planning is a must as is driving the site prior to data collection to establish safety hazards and traffic levels at certain times. Reedy claims there is more planning required for mobile scanning than for other technologies.

“Today, even with GPS or RTK, you don’t normally worry about the satellites very much because you can judge it on-the-fly. With this, because you’re going to be collecting for certain hours, you don’t want degradation of your GPS signals. You want that consistent because the accuracy is based on that GPS—the key component to setups.”

Lasers are another aspect of the technique that offer room for improvement, and Reedy already sees that happening. “The lasers will become more accurate and [there will be]fewer of them. We were seeing that at SPAR with some of the real-time technologies that spin out more points faster.”

Future Possibilities

To date, DEA has collected about 200 miles of data via mobile scanning. The company’s focus will remain on transportation and rail jobs, but it hopes to add large-site facilities such as airports to its roster.

“It’s all going to link up to, in the future, intelligent transportation systems,” Reedy says, “and having a good three-dimensional inventory of your assets is one of the key components. This is obviously a way to collect this data—efficiently.”

This is what ODOT’s Ron Singh believes. The chief of surveys/geometronics manager is lining up a rigorous mobile scanning comparison test to prove the technology’s assets. In addition to airborne helicopter LiDAR trials by John Chance Land Surveys using its FLI-MAP system, ODOT will evaluate the mobile scanning technique to ground-based total station surveying, fixed-wing photogrammetry and low-flying helicopter photogrammetry. Why mobile scanning?

“For generations, we have been using the single-point positioning method where, for example, if we’re trying to make a map and the surveyor wants to show the position of a manhole, they have to physically walk out to that manhole and take a measurement on it,” Singh explains. “With scanning in general, that has changed the concept in several ways. One, it has allowed us to capture a virtual world essentially … and two, it has changed the idea of single-point positioning to something different … something that’s using lots of data to compute a position.”

Singh says stationary scanning has worked for some time but it is, by today’s standards, “too slow,” especially on long corridor projects with a lot of detail. “Mobile scanning … allows us to capture a lot of data very quickly.

“It’s very clear to me that it’s going to have a huge impact on safety and productivity. It’s still going to take time to produce the maps, but the data capture will be much more efficient, much more safe, and in some ways, is a better snapshot in a certain moment of time (since things change during the duration of a project).”

He and his team will test these theories, as well as some related to overall cost, final product accuracy at a 95-percent confidence level, data-collection speed and disruption to traffic safety in the technology trials to be conducted this fall. “Equally important but harder to describe would be trying to determine what really can be expected from the system,” Singh says. “In other words, would expecting the system to locate and map small objects such as water meters or locating objects in grassy or brushy areas be expecting too much? Every system has its strengths and weaknesses, and we would like to learn what those are.”

DEA will conduct scanning using its Terrapoint TITAN system, and WHPacific Inc. will conduct scanning using its Optech LYNX Mobile Mapper. “Our purpose is to evaluate the capabilities of these emerging technologies and determine the applications and conditions where it is best used on highway projects,” Singh says.

In the long run, Singh says he thinks mobile scanning could advance some services of ODOT. The collection of digital video logs ODOT currently provides, which is a still-image pictorial record of state highway features from a driver’s perspective, could potentially be enhanced—or replaced—with mobile scanning (point cloud and video) images. “I think it’s a good spinoff of this technology,” Singh says, adding that this is his own personal idea and not an official ODOT plan. “If that’s the case, we might want to scan entire highways.”

Singh says mobile scanning “is the emergence of something new that’s going to change how we do a lot of survey work.” And what’s more, he says, is that “mobile scanning as we see it today is in its very infancy.”

What about accuracy?

Shortly after we published this story, Dan Hoelscher, P.L.S. from the The Upchurch Group, Inc. in Mattoon , IL wrote to ask “What kind of specifications for accuracy do they have? It seems to me that the tolerances wouldn’t be tight enough to establish a profile for a bridge job as Mr. Reedy states in his article. I don’t know how the process works but if you are traveling the highway, going over bumps and using some type of RTK for your position you would be lucky to be within a foot in elevation.”

Marcus Reedy responded with “This system has integrated components and GPS is just one of them. The system also includes a robust IMU unit which accounts for the bumps, etc.. All the data is post processed, so it’s not based on traditional RTK GPS methods. The vertical accuracies we are seeing compared to traditional ground based surveys are from 0.06′ to 0.12′ depending on the range from the scanner and GPS constellation at the time of collection.”

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