Laser scanners and software provide accuracy and time savings for infrastructure asset management and rehabilitation.
By Bob Drake
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As infrastructure owners, operators, and managers strive to accomplish more with less money, surveying and software technologies are helping civil and structural engineers meet the challenge. “Experts agree that more than $41 trillion will need to be spent on global infrastructure projects over the next 25 years,” said Terry Bennett, senior industry program manager for Civil Engineering and Planning at Autodesk. “Many of these will be large, complex, high-risk projects set in confined urban environments that require a precise and accurate 3D spatial assessment of the existing infrastructure conditions.”
Obtaining accurate as-built information often is the foundation for asset management and rehabilitation projects. “Laser scanning and the rapid creation of rich 3D models have changed infrastructure development from a 2D profession to 3D,” Bennett said. “We now have the capability for 3D modeling tools, such as AutoCAD Civil 3D 2012, to interrogate rich point clouds, captured by aerial LIDAR, mobile, or terrestrial laser scanning. From here we can extract limitless 3D information providing 3D existing conditions that are comprehensive, precise, and accurate. This results in the reduction of mistakes, saving weeks or months on projects, and more importantly, providing rich 3D models useful throughout project lifecycles.”
The following descriptions of recent projects and applications demonstrate some of the capabilities that laser scanners offer.
Railway tunnel clearance
One of America’s important railways received a facelift as work was completed in 2010 on the Heartland Corridor. With the goal of facilitating efficient travel on rail lines from Norfolk, Va., to the Midwest, the public-private partnership between the Norfolk Southern Railway (NS), the Federal Highway Administration, and the states of Virginia, West Virginia, and Ohio included renovations to existing infrastructure. As part of this project, 28 tunnels were cleared and 24 overhead obstructions removed to accommodate rail cars with double-stacked shipping containers. Blacksburg, Va.-based Anderson & Associates (A&A; www.andassoc.com) was selected to scan the tunnels to ensure clearance for the larger railcars.
While the centers of the tunnels had clearance to accommodate the railcars, rounded corners at the entrances posed potential problems for the squared outside corners of the cars’ rooftops. A&A specializes in civil and environmental engineering, surveying, planning, and landscape architecture. In operation since 1968, the firm is well-equipped to handle a project of this scope.
Obstructions were addressed during the construction phase of the project using conventional equipment such as total stations. However, this approach introduces uncertainty by relying on visual observation to select the cross-sections that appear to be the lowest point in each tunnel section. “If traditional methods would have been used to validate this project, it would have been nearly impossible to ensure that the entire distance covered by the survey was free of conflicts,” said Assistant Survey Manager Justin Lewis.
Instead, A&A turned to FARO Technologies’ laser scanner. This phase-based scanner captures as many as 976,000 measurement points per second. When implemented with FARO software, A&A could make quick judgments on a tunnel’s clearance. Survey technicians established control points at tunnel entrances with a GPS. Using a series of reference spheres, the technicians traversed the tunnels, scanning and recording reference points with the GPS. “We found we could collect field data on the typical 1,000 foot tunnel in less than six hours,” said Joey Conrad, survey technician. Such a job normally might take as long as 15 hours.
The various scans were imported into FARO Scene software, enabling the data points to be merged into one continuous set. Real Reality Tunnel software was used to run a template for a double-stacked train across the centerline for the entire tunnel. A&A was then able to produce cross-sections of conflicts and provide them to contractors for rework and recheck by A&A technicians. After the structure was verified as conflict-free, the final drawings were provided to NS.
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“The scanner turned out to be ideal for this project,” said Lewis. “Its high scanning speed made it possible to complete the job in a fraction of the time required by the conventional method. We got the job done right on schedule.”
Information provided by Faro Technologies
Highway bridge as-built
The Michigan Department of Transportation (MDOT) currently is working on a project to replace the northbound bridge deck for the I-275 bridges spanning the Lower Branch River Rouge in Canton Township, Mich. The northbound and southbound bridges, originally constructed in 1976, carry a great deal of traffic on a daily basis. The challenge for the team of engineers on the project (which is currently in the planning stages) was to locate accurately and in a timely fashion all of the cylindrical piers that support the northbound bridge decks.
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The team, which included Great Lakes Geomatics, immediately concluded that conventional survey methods would be too time consuming and not economically feasible. Additionally, to obtain the existing elevations and locations of the bridge deck surfaces by conventional survey methods would require intermittent lane closures, which MDOT wanted to avoid.
Laser scanning allowed the Great Lakes Geomatics team to obtain the data required by MDOT without lane closures, accurately locating piers and measurements of the undersides of the bridges. Laser scanning also kept survey crews out of the path of freeway traffic.
Point clouds were obtained using a Leica HDS ScanStation 2 time-of-flight laser scanner and a Leica HDS 6000 phase-based laser scanner. The ScanStation 2 obtains 50,000 points per second at a range of up to 300 meters; the HDS 6000 obtains as many as 1 million points per second at a maximum range of 79 meters. The long-range scanner allowed the team to tie the two bridges together and obtain coordinates outside of the HDS 6000 range. The individual coordinates were extracted from the point clouds using Leica Cyclone virtual survey software. Autodesk BIM for Infrastructure solutions allowed for the 3D point information to be uploaded so that the 3D bridge deck and surrounding surfaces could be created. The data also was used to create conventional 2D drawings as deliverables.
The laser scan surveys took about 24 hours to collect the point cloud data on each bridge. Drafting required about 60 hours to select the points and prepare the drawings for each bridge. According to the Great Lakes Geomatics team, it would have been impossible to obtain the level of detail with conventional survey methods and cost savings can be determined only by estimating the amount of time that would have been required for lane closures.
Additional benefits of the laser scanning survey are that other points can be extracted from the point clouds without returning to the site. The point cloud is historical information that can be used at a later date to verify exiting conditions prior to construction. A free viewing software tool called Truview by Leica can be used as a communication and measuring tool. The software allows the viewer to simulate the individual scanner setup locations. The software can create .XML markup files that can be distributed to clients or coworkers. The program allows for measuring within each of the laser scanner setups.
Information provided by Great Lakes Geomatics
Mine site surveys
Most surveying professionals know that 3D laser scanning technology can make their job safer and easier, completing surveys eight to 10 times faster than traditional methods with far greater resolution. Integrated hardware-software systems offer the most value by optimizing data acquisition and processing workflow.
I-Site laser scanning technology developer Maptek has visited mines across the United States, demonstrating how to realize a further 50-percent gain using mobile laser scanning. The Maptek I-Site 8800 truck-mounted scanner demonstrates the speed and accuracy of data capture.
The I-Site 8800 has a range of up to 2,000 meters and is designed to be used in the high-vibration and dusty environment of the mining industry. The mounting plate for the I-Site 8800 scanner can be fitted to any vehicle – tractors and utility vehicles have been used to access locations inaccessible to light duty-vehicles.
I-Site Sales Director John Dolan recalls scanning a leach pad half a mile long and quarter of a mile wide in 2.5 hours with 22 setups. The vibration-absorbent mount allows the scanner head to remain on the vehicle when moving around the active site. The leach pad was modelled and ready for volume calculations by the time surveyors returned to the office. In another case, an entire tailings pond was scanned in a day. Data from 44 scanning setups was processed and delivered within 48 hours, compared with days – or even weeks – with aerial photography.
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Using the I-Site 8800, large open pit mines can be scanned in one day, generating toe-crest data plus detailed surfaces and contours within 24 hours of scan completion. The same survey effort provides detailed surfaces of complete benches as well as the toe-crest data normally used for as-built analysis.
Scan data is processed in the cab of the Maptek truck on the same laptop that acquires the scan and GPS data, making the import of data seamless. This allows the scan data to be updated, registered, and viewed while driving. Holes in the data are able to be spotted and filled in while in the truck, rather than discovered back in the office. The vehicle-mounted scanner eliminates the 5 to 6 minutes for tripod setup time at each scan location, leaving only 3-1/2 minutes scan time on average.
Intelligent filtering of data in I-Site Studio software reduces the high-resolution point clouds to data that can be used by all CAD-based software programs. Accuracy is not compromised because redundant laser points are removed and can easily be checked against GPS ground shots for verification.
Laser scanning, using the latest technology, represents the future reality of mine survey. Mine operators find the solution to be cost effective, delivering measurable safety and accuracy key performance indicators, cutting survey time by 65 percent, producing reports in hours rather than days, and increasing detail for improved mine planning.
Information provided by Maptek
Railway asset surveys
RIEGL USA, in partnership with EarthEye LLC, performed a railway collection project to demonstrate the abilities of the RIEGL VMX-250 to acquire railway data. The main object was to collect the positioning of railway signals and features. Secondary objectives were to determine the ability of the system to collect track profile, ballast, and gauge information. EarthEye LLC collected stereo camera data to aid its feature extraction study on railroad asset management. A stretch of 10 miles was closed to rail traffic for a period of two hours. All 10 miles were collected during this time period with the VMX-250.
The VMX-250 hardware consists of two RIEGL VQ-250 2D laser scanners, an INS-GNSS unit, and an on-board computer fitted into a portable case. The INS-GNSS unit includes all of the electronics for real-time kinematic (RTK) and three sensors: an inertial navigation system (INS) sensor, a global satellite navigation system-receiver (GNSS) including antenna, and a wheel sensor (distance measuring indicator).
Mounting the RIEGL VMX-250 on a Hi-Rail vehicle was accomplished using two mounted racks that bolted into the truck bed. A Honda generator was used to charge the main power supply – a car battery.
RIEGL’s RiPROCESS software package was used to process and analyze the collected data. RiPROCESS uses RiWORLD and other RIEGL software utilities to project collected target returns into georeferenced points. The VQ-250 uses advanced signal processing and digitalization to extract targets from the returned full waveform pulses in real time. This allows the focus of the VMX-250 user to be on processing the best possible trajectory, while still producing quality data quickly. The total project generated 134 GB of data including exported LAS files. Processing time was about five to eight hours, including exporting and quality control.
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Using the view capabilities of RIEGL’s RiPROCESS, the cross section of several points along the railroad can be analyzed. A feature extraction software package such as TopoDOT can use the partial profile to fit the type of rail beam to the data collected. This is important since it is not always possible to traverse every single track in a rail yard or along a stretch of rail with a second parallel track. This is mainly accomplished by defining the rail profile and fitting it to the scan data.
RIEGL’s VMX-250 performs well on a Hi-Rail vehicle and provides an ability to collect feature information quickly and rail location information for use in third-party software point cloud feature extraction software. The compact mobile LiDAR system can be integrated on new vehicles without modifying the vehicle permanently. The rail data collected gives users many additional capabilities that traditional surveys and airborne laser scans do not. With efforts across the country to add digital speed control to the U.S. railways, RIEGL’s VMX-250 is an effective tool to use in completing this effort.
Information provided by RIEGL USA
Offshore oil facility as-built survey
Laser scanning is a far more efficient surveying technique than using conventional practices on large structures with extremely tight design tolerances. Dale Stockstill & Associates (DS&A), a provider of surveying, mapping, and laser scanning services on the Gulf Coast, recently developed an as-built survey of a five-story accommodation module and helipad – a vessel that serves as living quarters for oil workers – using Topcon Positioning Systems’ GLS-1000.
The structure was scanned on all four sides and top and the point clouds registered in Topcon ScanMaster software. DS&A also provided color maps of the bulkhead walls, which showed the amount of “hogging and sagging” in the bulkheads. The 3D model of a given section and the cloud were placed together in PolyWorks software. The color map that DS&A presented to the client revealed a color-coded picture of the structure represented by different colors for each specified measurement range. The color-coding allowed the client to define the deviations to a structural engineering firm to analyze the as-built structure in a global structural analysis in order to certify the integrity of the accommodation module. It was critical for fabrication tolerances to be within tolerance because of the direct relationship to the results of the initial structural analysis.
Topcon’s newer GLS-1500 speeds up point cloud collection at a rate of 30,000 points per second and a range of 150 meters. The unit’s “all-in-one” design also reduces the amount of equipment needed in the field. It has a built-in 2.0 megapixel digital camera, so when it is connected to a PC and used with Topcon’s ScanMaster software, a live video feed of the job site can be streamed to aid in scan setup and data acquisition. Also, it has an onboard data collector with a keypad and LCD display that allows use as a stand-alone laser scanner. Data collected can be stored onboard on a SD memory card or logged into a PC. A built-in wireless LAN connection allows control of the scanner on a PC from the inside of a vehicle.
Topcon Precise Scan Technology is designed to allow high-accuracy measurements over a wide range of distances. Lens array optics technology maintains distance accuracy from 1 to 150 meters; additional ranging past 330 meters is available. The unit’s Class 1 laser classification allows scanning near airports, busy traffic areas, and populated areas, as well as low power consumption and fewer battery changes.
Information provided by Topcon Positioning Systems
Bridge rehabilitation
In December 2008, a routine inspection of the Chaudière Bridge linking Ottawa, Ontario and Gatineau, Quebec, revealed structural cracks in two of the bridge’s masonry arches. Because the Chaudière Bridge is a crucial interprovincial connector, Public Works and Government Services Canada (PWGSC) determined that both arches needed substantial rehabilitation.
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The project provided engineering and logistics challenges. Because of the 180-year-old bridge’s historical significance, its original structural characteristics needed to be preserved, and traffic demanded that restoration occur without closing the bridge or impacting the Ottawa River. Engineering teams developed a plan to install prefabricated concrete support panels into the arches, and PWGSC awarded the construction contract to Peter Kiewit Sons’ Infrastructure Group. Denis Dubois, arpenteur-géomètre inc in Saint-Bruno-de-Montarville, Quebec, was selected to provide surveying services.
The restoration required detailed measurements of the existing structure. “This work is ideal for 3D scanning,” Dubois said. “It’s a challenge to capture the precise shape of an arch. Site access was difficult, and conventional total station surveys would be time-consuming and could not produce a comprehensive view of the arches.” The measurements needed to be absolutely correct. Once the panels were fabricated and delivered, they could not be changed.
To gather the information, Dubois combined GPS and 3D scanning to create a georeferenced 3D model of the arches. After establishing five control points via RTK GPS, the team used a Trimble VX Spatial Station to conduct the scan. Occupying the GPS points along the river, they collected 80,000 individual 3D points in roughly five hours. The points, spaced 2 inches apart, were measured with a precision of 1/8 inch and tied to the local geodetic coordinate system. In the office, the surveyors used Trimble RealWorks Software to integrate the scans and deliver 3D surfaces in DXF format to the client.
After comparing the point cloud to previous engineering data, Kiewit Project Engineer Robert Cornell was confident they had the spatial and positioning information to build the arch panels. “I was surprised by how Denis used the VX to shoot the bridge with that amount of precision,” Cornell said. “The point cloud gave us the confidence to design and build our prefabricated panels with assurance that we could successfully complete this project.”
Dubois said that the precision measurements and dense data were the keys to success. The data revealed irregularities in the arches that conventional surveying might have missed. “We produced better information in less time,” Dubois said. “Without the scanning functionality, fieldwork would have stretched for many days, and produced less detail.”
Seven months after the initial survey, twelve 20-ton concrete arch panels were ready for installation. Dubois’ survey team returned to the site, this time using the Trimble VX as a robotic total station to set control and align rails used to move the panels into place. Less than two years after the discovery of the deteriorating arches, the restoration was complete and all four lanes of the Chaudière Bridge were re-opened to traffic and pedestrians.
Information provided by Trimble