Northern Lights: GNSS Machine Control
Professional Surveyor Magazine - April 2011
Surveyor’s Friend or Foe?
Norm Coté, PEng, NBLS, CLS, SLS (Ret.) and Mike Wolfe, MScF, PE GNSS
New, integrated technologies and systems have been changing the role of the professional surveyor. Ultimately, we are still responsible for the spatial accuracy of a project, but now we can assist in adding greater value and productivity to the job. This article profiles two surveyors operating in Atlantic Canada who have embraced new technologies—including cell phone networks, cloud computing services, GNSS correction services, lidar and scanners, and machine control devices—enabling services beyond the traditional scope of the surveyor.
GNSS VRS Surveys
Mike Wolfe is the former GNSS infrastructure engineer for the largest GNSS correction service in Canada; this system has more than 180 reference stations and 11 VRS (virtual reference station) coverage areas across four time zones. One of the first geomatics innovations employed on the project was the acquisition of a 55km-long terrain model using lidar. (This terrain model has been used extensively for highway design and quantity calculations.) Huge areas of terrain were modeled in a short period, which was an important consideration in this time-sensitive infrastructure project. Lidar data was ground-controlled throughout the project with GNSS VRS surveys. Typically, one would expect the field survey to ground-truth the lidar data. Ironically, at times, the lidar terrain model detected instrument height blunders in the field survey data.
As the GNSS infrastructure manager for a national VRS service, Mike had to gain knowledge outside of traditional surveying expertise and into the realm of computer networking and telecommunications. Mike’s initial knowledge of networking was limited to his own home network with a basic modem and wireless router. Leveraging that basic understanding with a little formal and informal (Networking for Dummies) knowledge allowed him to scale connectivity to more than 130 GNSS reference stations across Canada with use of very sophisticated GNSS infrastructure software systems. The vast majority of the network connections were enabled with major internet service providers, but some connections were more challenging, such as satellite-based internet service providers or the old “squeaky-squelchy” dial-up modems.
For a real-time, internet-based GNSS correction system to work, observation data from a reference station is passed over the internet to a server. The server creates correction services (VRS or single station) that are then sent back to a field user. In the case of the system Mike was managing, this data flow may have travelled over 7,000 kms, through Bluetooth, cell phone, and internet connections. Trouble-shooting connectivity issues over four time zones made for some very tiring challenges.
Traditionally, a professional surveyor or project manager on a highway construction site would have managed several field crews that would set control on the construction site, perform topographic and drainage surveys, create profiles and cross-sections, lay out roadway design alignment, set grade and slope stakes, and calculate quantities. Managing and tracking all the data and personnel would be a time-consuming and daunting task, especially on a large project. Using advanced machine control and spatial management systems reduces these challenges.
GNSS Machine Control
Duane Doucette is the survey manager on a major highway construction project in Eastern Canada. He has implemented and facilitated one of the largest GNSS machine control systems ever developed for a construction project in North America. To do so, he has embraced new spatial technology tools to achieve significant productivity gains.
Duane’s work is challenging in that he must stay on top of the learning curve by constantly finding solutions that push the realm of traditional surveys. Trouble shooting is not so much a frustration but more of a rewarding process that challenges his analytical solu-tion-finding skills. His company has supported his efforts to use all the spatial engineering tools available to him; many productivity gains have been realized thus far.
This highway constriction project relies largely on machine control systems, and as the survey manager Duane ensures data is structured and flows effectively from design parameters to the machine control systems. No longer are plan/profile and cross-section drawings required for the corridor construction. Instead, 3D polylines of the sub-grade surface are created by the designers and digitally transferred to the machine control systems. Validation checks are run in the office, and a machine control emulator is used to ensure that the grading data is properly formatted and ready to be transferred into the machine. Currently, the grading files are handled manually by the site foreman and installed into the grader via compact flash cards. In the near future all design data and grade monitoring will be transferred via the cell-phone network in real time, as are the RTK/VRS corrections.
The GNSS positioning system on the equipment uses two antenna receivers that are mounted on sturdy masts, well above the cutting edge of the excavator or grader. GNSS satellite signals are tracked by the receivers and augmented with the VRS correction data that is streamed by an onboard cell modem to generate an accurate 3D position. This information, in conjunction with the machine’s dimensions and geometry, is used to determine the precise horizontal and vertical position of the blade in real time.
On this project, the vast majority of earth is moved by GNSS-enabled machine control systems, but not all of the systems are guided by GNSS; some are using a robotic total station for positioning. This system is used on final grades to achieve greater accuracy, in the order of 4mm. The machine also can operate under and around overpass structures and large rock cuts where a GNSS-controlled system might lose satellite lock and initialization more frequently. Only one end of the grader blade is positioned with an active prism target, and the cross slope of the blade is positioned with tilt sensors. A field surveyor is dispatched on site to set up the robotic total station in a location away from heavy equipment but with a clear view to the grader and control points. The control is usually established with a VRS/GNSS observation and/or using resection method from existing corridor survey control.
Duane says the equipment operators and their machine control systems are an integral part of his field crews. Machine operators are completely embracing the technology, and other operators want the systems on their rigs so they, too, can take advantage of the productivity gains. The in-cab display shows a plan view and a cross-section view. Additionally, a light bar display view can be used as a visual indicator for cut/fill and alignment guidance. Depending on the type of equipment and duty, the machines have been configured to operate using fully automated hydraulic blade adjustments and real-time elevation control feedback. Even the site foreman’s truck is GNSS-VRS enabled with a tablet PC, allowing real-time checks of grading jobs as he drives over the alignment.
Geodetic control costs have been significantly reduced since a VRS correction service has been established over the entire project area. Survey activities focus on verification of accuracies instead of establishing and maintaining control. Survey control costs have been reduced tenfold. Field surveyors concentrate their work on structures, as-built surveys, and detailed site surveys while grading surveys are addressed by the machine control operators, the “extended field crews.”
Duane finds it gratifying to assist in the development and modification of the machine control monitoring system. Since his initial design and development of the GIS-based construction management system, it is now web-enabled so that all levels of the construction process can be accessed. The drawing management system and scheduling system also are all spatially based.
These surveyors have embraced new technologies and have successfully transformed the traditional survey work environment. They’ve incorporated change and constant learning into their work practice. Trouble shooting is considered a rewarding challenge rather than a stressful undertaking.
Surveyors have been bringing data from the field to the office and from the office to the field for centuries. They have been integrating field measurement systems with data collection systems for decades. Evolving positioning and data-transfer technologies optimize the method and speed of this integration. By accessing the myriad of these technologies, the line between office and field begins to fade, and surveyors evolve to become more effective and competitive solution providers. Friend or foe? You be the judge.
Norm Coté, PEng, NBLS, CLS, SLS (Ret.), is a founding member and chair of Professional Surveyors Canada, with more than thirty years of practical and administrative experience in the surveying industry. Currently he is the assistant director of surveys and property titles with the New Brunswick Department of Transportation in Fredericton, New Brunswick, Canada.
Mike Wolfe, MScF, PE, has more than fifteen years of experience specializing in GNSS (GPS/GLONASS) infrastructure, electronic field data collection, GIS spatial analysis, and client support. Currently he is the engineering surveys manager for the New Brunswick Department of Transportation.
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