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Home arrow Archives   The American Surveyor     

LiDAR Hits the Rails Print E-mail
Written by Larry Trojak   
Friday, 23 August 2013

A 2.656Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

Much like the apps that proliferate on our smart phones today, LiDAR is one of those technologies for which the possibilities seem, quite literally, endless. Already proven in a host of survey and construction-based operations, LiDAR has also proven its value in peripheral applications such as mining/aggregate inventory, forensic work, utility line inspection, GIS data gathering, and more. To that list, thanks to an ongoing project for the Wisconsin & Southern Railroad (WSOR), you can now add rail line clearance inspection. As part of a bridge maintenance program TerraTec Engineering, LLC (TerraTec) recently wrapped up the scanning of more than 570 miles of WSOR track using an IP-S2 LiDAR-based scanning system from Topcon Positioning Systems. When the full project is complete, TerraTec will present the railroad with a comprehensive database of potential clearance conflicts, as well as a point cloud scan of the full route (along with corresponding photo documentation) allowing the railroad to improve its shipping and maintenance efforts.

Progressive Rail Industry
For many, railroads conjure up mental images of a stodgy, passé form of transportation utilizing outdated technology. In actuality, however, the rail industry is quite progressive, using everything from ultrasonic sensors to detect cracks in wheels, to onboard GPS for fleet navigation and tracking. So, according to Jeff Francis, co-owner and principal with Cedarburg, WI-based TerraTec, it should not be surprising that, when soliciting bids for companies to play a key role in their bridge maintenance program, WSOR insisted that the effort include LiDAR-based technology.

"The railroad had a very definite plan in mind when they set out to do this," he said. "They wanted proposals for a bridge management project and we won the bid as a sub-consultant to Graef USA, the prime on the job. The overall project is to rate, evaluate and create a management plan for their bridge system, but a major component of it specified that the company chosen had to scan the bridges and the corridor for clearance purposes."

TerraTec responded to those needs with Topcon's IP-S2 LiDAR-based mobile scanning system which they leased from the Waukesha, WI branch of Positioning Solutions Company (PSC). Other choices available to them included the IP-S2 HD which offers a high-density, long-range LiDAR sensor for maximum visual mapping detail, as well as a host of advanced positioning and mapping features.

"We were confident that the IP-S2's range of features, including the Ladybug camera technology it offers as standard, were an ideal match for the project at hand," said Francis.

Scanning Rationale
While LiDAR scanning is not something the WSOR normally does, Francis said they requested it to help them better understand the clearance envelope within their network.

"The long-term goal for the railroad was simple: if a shipper calls them with a load size, they want to be able to input that information into a database and immediately be able to determine where conflicts on the system might occur. They felt that scanning was the best way to start making that happen. We took it a step further and proposed creation of a database into which they would be able to input a load parameter to determine where--based on our scanning sessions--their choke points or conflicts would be."

According to Francis, a common choke point on a railroad might be a bridge or other structure that is hard to manipulate or modify without some major investment. There are, however, many conflicts on the line that can be easily resolved--vegetation growth that can be cut, signals that can be relocated at crossings to widen clearances, posts or mile markers that can be relocated, etc.

"We typically think of a railroad as a boxcar or flatcar with a standard size width," he said. "But railroads do, in fact, carry some unique loads at times. Here in Wisconsin, wind turbine blades and towers are frequently being shipped and, because of their unique size, the railroad needs to know where on the system that load will be clear and free of the risk of damage. This will allow that to happen for the WSOR."

Making Tracks
With the IP-S2 leased from PSC, mounting the system onto a rented Ford F-250 hi-rail vehicle was the next challenge. According to TerraTec's Bob Schmalzer, PSC had a vehicle rack and mounting system that they've been using and shared that design with them. Because TerraTec's vehicle was a rental, however, permanent changes couldn't be made to accommodate the rack as designed.

"We were able to take that design, use it as a guide and create a new rack design with a mounting plate and mount it to the rental without damaging the vehicle at all."

Scanning itself was done in two phases. Schmalzer (accompanied by a pilot supplied by WSOR) first rode the entire network to establish control points on bridge structures and at crossings.

"During that pre-scan run, we also magnet-mounted a GPS unit onto the center of the truck's hood and, working through the WISCORS Network, collected a centerline, top of rail point at 100-ft intervals," he said. "By doing that, when we came back to do the actual scan, we could run two 20-mile segments using a static GPS station point within that line. And, because we were scanning those control points, we could then tap back into them during post-processing."

The 20-mile daily scan segments to which Schmalzer refers, were often dictated by train movements for that particular day, as well as where the railroad had rail car storage, and other needs the railroad might have had that day. "There were even times when we came upon a train that had stopped on the tracks because the train's crew had timed out," he said. "So we'd have to get off the tracks, leave that section, re-rail past the stopped train, and come back to scan the missed part another day. In such cases, having the railroad pilots, onboard with us was a real help."

IP-S2 Anatomy
The IP-S2 used by TerraTec consists of three high-resolution LiDAR scanners to generate a 3D point cloud that captured everything the hi-rail vehicle encountered as it rode WSOR's rails. The system runs on a cab-mounted laptop into which all the data is collected and stored.

The IP-S2 control unit has multiple sensors and a dual-frequency GNSS receiver that tracks both GPS and GLONASS signals to maximize positioning by determining the vehicle's position and attitude on a real-time basis. Vehicle wheel encoders compare rotation speeds, improving positioning accuracy even further.

The Ladybug camera system, which Francis sees as a key component of the whole package they will present to WSOR, captures 360° digital images at a rate of six pictures every three meters. The images are then stitched together in post-processing to produce a spherical street level-type photo that can be accessed in conjunction with the point cloud data.

"In addition to the database itself, we will also provide WSOR with data that we've gathered, along with Spatial Factory software viewer," said Francis. "With these, they can then go through the Ladybug photos at their office--essentially walking their entire system--and be able to visually see the conflicts that are called out in the database and determine how to best address them: `Do we move the fence post?' `Should we cut the tree down?' `Do we reposition the sign?' From that point, it will be a simple matter to create work orders and dispatch crews armed with photos and imagery to help them in their effort."

At Day's End
Post-processing data for hundreds of miles of track is, obviously, an intensive undertaking. Francis estimates that, for every hour of scanning completed, an equal hour of time is being taken to run the data through Geoclean, the Topcon software bundled with the IP-S2 that handles all the data processing.

"Geoclean takes the various types of data gathered by the satellites, the Ladybug camera, and so on, and brings it all together to create one unified subdirectory. That subdirectory, in turn, is what we access via Topcon's Spatial Factory to pull out the features we need. We really like the fact that, coming out of Spatial Factory, we can view the data in a number of different ways, including on a background Bing-type map, in a 3D format, or in a panoramic view."

The last bit of processing will include the use of TopoDOT, a CAD-based application from Certainty 3D which will allow TerraTec to further manipulate the data and generate the database which will be turned over, along with the scanning data, to the railroad.

Scanning in Their Future?
Francis said the WSOR project has been extremely successful, and even with 14-hour days, has been an interesting departure for them. They also found that, despite being the powerful tool that it is, the IP-S2 was extremely easy to use.

"Once we learned the basics, it essentially became a plug-and-play system for us," he said. "For each outing, we would get it mounted on the truck, connect the cables, hit `Run,' let the satellites configure themselves, do a two-hour scanning session--just to keep file sizes manageable--close that down, and start the next run. The whole process was very smooth.

"We see a real long-range value in other industries for which clearance issues are a concern. This is one of those tools for which new uses will continue to arise and we now have the experience under our belts to gain a competitive edge."

Larry Trojak is a communications writer for his own firm, Trojak Communications, in the town of Ham Lake, Minnesota. He is a frequent contributor to construction and survey magazines.

A 2.656Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

 
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