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Clouds roll in over the Sandia Mountains as Topcon trainer Oscar Cantu sets up a reference station demonstration for Albuquerque's GPS network. Topcon made a contribution to Central New Mexico Community College to support technician training.

As bulldozers begin leveling the ground for Mesa del Sol, a 15-square-mile industrial, retail, and residential complex south of Albuquerque, N.M., everyone involved in the project—from private surveyors to city engineers—will be using the same set of reference points for all related infrastructure.

“Think about it,” says Cliff Wilkie, the city's geodetic surveyor. “Everyone is using the same data based on the same network of control. No more finger pointing when things don't work out quite right; no more streets, sewers, and pipelines that don't quite meet; no more lawyers and lawsuits to assign blame for mistakes. The indirect savings will be huge.”

Mesa del Sol is the first large-scale application of Albuquerque's Real Time Global Navigation Satellite System—GNSS—Network (ARTGN), the world's first government-owned, triple-constellation-capable, real-time GPS network.

The product of more than three years of effort by the Albuquerque Municipal Development Department, the network consists of five continuously operating base stations equipped with a Topcon GR-3 GNSS receiver. The receivers, which use the U.S., Russian, and soon-to-be European satellite constellations orbiting the earth, are connected to a pair of Hewlett Packard ML350 servers located in the city's data center, a redundancy that ensures 24/7 availability should one server go down. With Livermore, Calif.-based Topcon Positioning Systems Inc.'s TopNET networking software processing incoming data in real time, crews use their cell phone or radio to access up-to-the-minute positioning corrections.

“Anywhere inside the polygon formed by the five stations, the software creates a virtual reference station,” says Wilkie, who came up with the ARTGN concept in 2004. “That means a surveyor can walk around anywhere in that area with a rover on a pole and get centimeter-accurate observations, just as if a mobile GPS base station were operating a few meters away.”

Outside the polygon, the surveyor switches to real-time kinematics technology that transmits information between a base station and a rover that are in radio communication, and continues surveying as usual.

Between the area inside the “box,” and the roughly 6-mile range of the base stations outside the “box,” the city's network covers more than 400 square miles. A surveyor working anywhere within that area needs only a rover on a pole and an ARTGN subscription to tap into the network.

A Money-Making Proposition

The city's new network began with a meeting between Wilkie and a dozen local surveyors and engineers. He'd been following developments in the global navigation satellite system and realized that Albuquerque was a nearly ideal location for a networked real-time system: it has a very high density of well-maintained control monuments, and surveyors had been required to make ties and show them on plat maps.

Encouraged by favorable feedback, Wilkie began testing the idea with people both inside and outside the city government. This led to a meeting with six local surveying firms and two land developers, including the firm involved in planning Mesa del Sol. All were open to paying a monthly fee to access the system.

The timing was right, too. The concept coincided with proposed changes to subdivision regulations. An ordinance change now requires surveyors to show reference to NAD 83 and NAD 88 values, which the city's new network supports. “We were already moving in that direction, so the additional changes were relatively minor,” says Wilkie.