GPS-Guided Earthmoving Gains Ground1 Jan, 2007 By: Andrew G. Roe,P.E.
Satellite positioning saves one contractor millions.
The practice of guiding earthmoving equipment with GPS (Global Positioning System) units has been gaining acceptance in recent years, and industry sources expect the trend to continue for the foreseeable future. Technological advances, an expanding user base and competition among vendors are all helping propel this growth.
Construction contractors have been at the forefront in implementing this technology, but designers are also playing a key role, because 3D models are required to represent grading surfaces for the GPS-equipped machines. The concept has opened doors for more collaboration and time savings through "stakeless" construction, but it has also raised concerns about data ownership, liability and accuracy expectations.
How It Works
GPS-based earthmoving systems use satellite data to compute the positions of GPS antennas mounted on construction equipment. Project-specific design information is loaded into an onboard computer that compares the exact position of the earthmover's blade with design coordinates and guides the equipment accordingly. The generated data can be used to drive fully automated blade control, or to guide a human operator by displaying grading information on an in-cab screen.
GPS antennas are visible on this earthmover, which can efficiently perform grading without construction stakes. (All figures courtesy of McAninch.)
Design information can be developed in AutoCAD- or MicroStation-based products, as well as other 3D-capable packages. The design data is typically transferred to another software platform compatible with the onboard computer and capable of presenting data in a contractor-friendly fashion. Additional products, such as Terramodel from Trimble Navigation, are often used by contractors to check data and visualize designs.
A high-school construction project near Kansas City was visualized in Terramodel before machine-controlled grading.
Recent enhancements to GPS, along with advancements in Russian and European satellite positioning systems, have improved GPS unit performance for contractors and other users. The U.S. system, introduced in the 1970s by the Defense Department, was upgraded in 2005 with the introduction of a new generation of satellites and a second civilian signal. Russia's GLONASS constellation, which fell into disrepair in the 1990s, has been revamped with additional satellites and an agreement to better share information with the United States. Europe launched its first Galileo satellite in 2005 and plans to have a fully operational system by 2010.
Expanded satellite access means less down time, better accuracy and greater reliability, says Tim Tometich, GPS division manager for McAninch, a West Des Moines, Iowa-based contractor and early adopter of GPS-based machine control. The broader range of positioning frequencies available, coupled with newer GPS equipment, "helps us initialize faster and lock in," he says.
McAninch helped GPS vendor Trimble develop and test some of the earliest machine-controlled systems, including the SiteVision system used by Trimble customers. Trimble has focused on developing technology jointly with equipment manufacturer Caterpillar.
Other vendors have also jumped into the fray. Komatsu and Topcon signed an agreement in 2004 to develop machine-controlled systems and consequently introduced 2D/3D AUTO BLADE, which includes laser-based blade-control systems. John Deere has introduced a line of dozers that are compatible with both Trimble and Topcon equipment. Topcon's new 3DXi GPS+ grade reference provides multiple views for equipment operators and can help prevent over-excavation, says Murray Lodge, Topcon's director of construction sales. "You save on materials and you will save time and money," he says.
Handheld GPS roving receivers are also improving, says Tometich. "We use rovers for slope staking, quality control and generating reports," he says. Software improvements have made user interfaces "more recognizable by contractors," he adds. For example, field crews can now view road cross sections graphically in real time, instead of interpreting x, y and z coordinate data.
The increasing use of machine-controlled systems is helping drive innovations, says Patrick Ruelle, a McAninch vice-president. "Machine control is so fully absorbed in the day-to-day operations that I think we all take it for granted. In the beginning, it was our site crews that came to rely on the new technologies. Over the past several years, our highway crews have become very proficient at using GPS tools."
While obtaining accurate 3D models has historically been a struggle for contractors, that issue is also abating, says Tometich: "We're seeing more files in 3D." If 3D models are not available, contractors must create models themselves based on 2D drawings. Designers are often reluctant to share 3D data, for fear it may be misused or out-of-date. When changes are made to a design, the machine-controlled approach means the 3D model must be fully updated, not manually tweaked.
In spite of the challenges, machine-controlled grading appears to be taking off. Although certain jobs, such as small projects and those without 3D data, will probably continue to rely on manual staking, most major grading contractors will likely apply machine control over the next few years. McAninch uses some form of GPS on 95% of its projects and has consequently saved millions of dollars in time and materials over the past few years, says Ruelle. With that kind of success, other contractors will surely follow its example.