When Topcon (Livermore, Calif.) introduced the GR-3 GNSS receiver in 2006, the company touted innovative design features and the use of cutting-edge technology as the reasons to take the GR-3 out for a test drive. Among these features are G3 satellite tracking, enhanced durability, expanded memory, several communications options and greater convenience of use.

G3 tracking gives the GR-3 access to 72 channels, tracking both GPS and GLONASS constellations, as well as the foundation to receive signals from the satellites of the Galileo system that is still in testing.

According to Sitts and Hill Engineers Inc.’s Rob Erb, a licensed land surveyor since 1979 and past president of the South Puget Sound Chapter of the Land Surveyors Association of Washington, the GR-3 has been a boon to his business. The director of surveying for the Tacoma, Wash.-based firm uses the unit with the Washington State Reference Network (WARN). The density of the state’s High Accuracy Reference Network (HARN) has enabled Erb and his team to use the GR-3 as a rover without relying on the base/rover configuration the firm initially purchased.

In fact, the use of the rover with the state’s HARN has convinced Erb to convert his base into a rover. “At the approximate additional cost of $6,000 I can turn the base station unit into a rover and have two complete setups that allow me to field another complete RTK GPS system,” he explains.

According to Erb, “[WARN] works so well in our operating area and for the types of surveys we do that we have had no uses for the base/rover configuration as of yet.” He says he expects the proposed addition of GLONASS and Galileo signals to WARN to optimize coverage. “At this time, GLONASS can only be used in the base/rover configuration,” Erb explains, “[but] there are plans to incorporate GLONASS into the WARN network. I also anticipate Galileo to expand the coverage to new levels when it comes online.”

The range of the GR-3 was put to the test recently when Sitts and Hill was contracted by a large farming operation to survey the farm’s boundaries. Erb’s preliminary research suggested that he would need to do a sectional breakdown in order to find the boundary lines of the client’s property. “What a great opportunity to use our new GR-3 [system],” Erb says. “I was congratulating myself on a brilliant stroke of genius and a little luck.” But, according to Erb, luck wasn’t on his side. “Not only was the key section corner missing, but several others in adjoining sections were missing as well that would have allowed us to re-establish the position of the obliterated corner.”

Using the Topcon GR-3, Erb was able to do the additional work necessary to complete the project. In order to re-establish the corners needed to properly retrace the farm property lines, Erb had to survey portions of seven sections. The end result, he said, was a happy client and a profit for his firm.

Surveyors with Compass Point set up a GR-3 as a base and rover.

It's All About Communication

The versatility of the GR-3 communications options is a feature Topcon’s Jason Killpack mentions when asked about the ability of the GR-3 to function in different environments. “The GR-3 has both radio communications as well as a GSM modem onboard,” says Killpack, Topcon’s senior product marketing manager. ”The radio options for the user are either spread spectrum or our new DSP digital UHF radio.” Spread spectrum radio technology is a radio signal that resists interference and jamming. Digital UHF radios operate on a line-of-sight basis and have wide bandwidth. Killpack adds that the receiver’s various methods of communication allow the GR-3 to function in the base and rover configuration from three to almost 25 miles.

“Typical operation between base and rover with spread spectrum [radio] is three to five miles, and an optional RE-S1 repeater can increase this range,” he explains. ”The new DSP digital UHF radio can go from four to seven miles, base to rover.”

The GR-3’s internal modem utilizes SIM card technology. By simply switching SIM cards, the user has a choice of cellular carriers. “With the GSM modems as the form of communication from the base to the rover, the range is not limited to communication of the differential correction, but that of the view of the same common satellites,” Killpack says. ”We have tested up to 40 kilometers utilizing this operation.”

For users with specialized needs, the GR-3 offers other communications configurations. According to Killpack, “The user can access a web-enabled Bluetooth cell phone, or utilize the serial port on the unit to cable to a third-party external modem.” If needed, the internal modem can be set up with a static IP address, though Killpack says that will likely incur additional charges from the user’s wireless carrier.

Mike McEvilly of Sitts and Hill preps a Topcon GR-3 GNSS receiver.

Fit for Any Job

Compass Point Surveyors located in Clearwater, Fla., has experience with the GR-3 in the base and rover configuration. Benjamin Wiser, project manager and principal of the firm, says that his company has “extensive experience” in the utilization of GPS technology in all aspects of surveying applications.

Among some of the projects Wiser and Compass Point have tackled recently are waterline projects in the western Nokomis community and in Seminole County. Wiser is also performing control surveys and construction staking for the Florida Department of Transportation to facilitate construction of new weigh stations along Interstate 4.

Wiser’s crews use both the GR-3’s radio and modem for communication, depending upon the specific needs of a given project. When asked what practical range his firm was realizing in the base/rover configuration, Wiser said, “Depending on site conditions, anywhere from a half mile to a mile in one direction.”

Compass Point also uses the unit’s internal modem. “It cost us about $40 to set up the [modem] cards, and they cost about $60 a month for service for each of the units.” As far as accuracy using the modem, Wiser says they are using the modems on the L-Net GPS network, Topcon dealer Lengemann’s Florida network (merging into Georgia).

Sitts and Hill’s Erb chose a cell phone to meet his communication needs. “We elected to go with a cell phone for our data link,” he says. “The cost of an internal modem was prohibitive when compared to a cell phone and we only had a choice of one provider. By using a cell phone, we simply added a data line to our existing phone provider and did not have to set up a separate account with another provider.”

One of the many convenient features of the GR-3 is the Bluetooth capability for communication with the data collector. While the initial setup and pairing of controller with receiver may take a little effort, the ability to work without cables can be well worth it.

The flexibility of communications options available with the GR-3 allows both Erb and Wiser to exploit the specific strengths and overcome the limitations of their regions, and satisfy the requirements of their projects.

Rock-solid Design

Another important feature of the GR-3 is the unit’s durability. The GR-3 is housed in a magnesium shell and built around an “I-Beam” frame. These features combine to give the GR-3 a 2-meter drop rating onto a concrete surface. The unit is designed to withstand inclement weather (-20° to +50° C) and has sealed external ports.

Some of the design features of the GR-3 won the unit an International Forum (iF) Product Design Award 2007, a prestigious design award in Germany. San Jose-based design consulting firm Whipsaw Inc. worked with Topcon on the GR-3’s innovative design. According to Whipsaw’s Dan Harden, some of the features recognized by the iF are the unit’s ergonomic design, weatherproofing measures and balance.

The battery packs for the GR-3 are designed to serve as a handle, making the unit easy to hold. The batteries are oriented vertically, keeping the center of gravity closer to the rod and improving the balance of the system.

With weatherproofing in mind, Topcon built the GR-3 with an antenna housed under a plastic and rubber dome. The dome overlaps the base and battery handle, acting as an umbrella in the rain. The SIM and SD media card slots are located under the batteries, affording them protection from the elements.

Little Room for Improvement

As with all field surveying equipment, battery life is an important factor to consider when purchasing equipment. Killpack says that the GR-3 should get nine to 12 hours of life from the battery packs, depending upon whether the unit is functioning as a base or a rover. Wiser and Erb say their typical battery life ranges from five to 10 hours. But they cite the “hot-swappable” battery feature as a plus, and say that battery power has not been a problem for them. If battery power becomes an issue on a long day for any user, the GR-3 also has a standard alkaline battery adapter.

Wiser says the features of the GR-3 he found most helpful and productive were the “Quick-Snap” mounting system, which makes affixing and removing the receiver from the pole faster and more secure. He also appreciates the “hot-swappable” batteries and the Bluetooth connection status light. He would like to see an upgrade that allows for longer range with the radios and would like Topcon to “come up with a way to switch back from modem to radio communication without having to use separate software on a laptop or data collector to change the internal setting.”

Erb says, “The unit’s software and data collector are very friendly, but I would like to see it even more user-friendly--to default to the coordinate system that we were last using instead of defaulting to lat-long every time the unit is shut off.”

Professional surveyors from Washington to Florida face drastically different conditions, weather and terrain, and the GR-3 offers an array of options and features to help them overcome those challenges. Though the GR-3’s ability to receive Galileo signals may not yet be useful, Topcon has made another step in the right direction with this durable, flexible GPS receiver. As Wiser reminds us, no tool is perfect for every project. But the GR-3 is a versatile tool to add to many surveyors’ toolboxes.