Any number of RTK GPS rovers on the jobsite can work within the range of a single Lazer Zone PLZ-1 transmitter (left) and a GPS base station (right). The Lazer Zone PZS-1 sensor for this grade management system is located just below the GPS receiver/antenna on the range pole. Machine control applications use the PZS-MC sensor.
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Topcon has just announced its newest and most advanced system, Millimeter GPS. According to the company, "this revolutionary new technology will provide a significant enhancement in the vertical-measuring precision of RTK (real-time kinematic) GPS positioning systems."
In creating its new Millimeter GPS system, Topcon essentially has supplemented its RTK GPS positioning system with a new laser concept, Lazer Zone. Unlike conventional lasers that create only a single plane of light, however, the Lazer Zone laser transmits a rotating (600 rpm) signal that fans out to a "depth" of 10 meters (33 feet). Lazer Zone, says Topcon, sweeps the jobsite with a "wall of laser light."
By combining the new laser with any Topcon RTK GPS system, says the company, the resulting integrated system can "generate vertical accuracy to within a few millimeters, compared to centimeter-level vertical accuracy of conventional RTK GPS systems." (Just for reference, a height of 3 millimeters, for example, is slightly less than 1/8 inch. The vertical accuracy typically claimed for RTK GPS systems is 0.10 of a foot, or 1.2 inches, or 30.5 millimeters.)
To implement Millimeter GPS on a typical jobsite, the user of a Topcon RTK GPS system needs only to set up one Lazer Zone transmitter, then equip each rover (mobile GPS receiver) on site with a Lazer Zone sensor. A simple set-up procedure allows the Millimeter GPS system to automatically calculate the three-dimensional location of the transmitter, which has a working radius of 300 meters (1,000 feet). When the transmitter's signal reaches the sensor, which is mounted on the rover's GPS antenna, the system decodes the signal and instantly calculates the height differential (transmitter-to-sensor).
Thus, says Topcon, the laser portion of the Millimeter GPS system can generate vertical accuracy rivaling that of a local positioning system, which uses a robotic total station to measure vertical distances. The RTK GPS portion of the system continues to determine horizontal positioning, typically with accuracy to within 6 to 12 millimeters (¼ to ½ of an inch). But, of course, the RTK GPS system remains fully functional, capable of providing both horizontal and vertical measurements if the Lazer Zone transmitter is not in use.
Extending working ranges
An unlimited number of RTK GPS rovers can work simultaneously within the range of the Lazer Zone transmitter. To enhance working range on large jobsites or in extremely steep areas, however, as many as four Lazer Zone transmitters can be linked, thus extending the working radius to 1,200 meters (4,000 feet), or to a working diameter of 2.4 kilometers (approaching 8,000 feet). With four transmitters, the vertical range of the system also increases to more than 40 meters (130 feet). RTK GPS rovers can move smoothly from within the working range of one transmitter to that of another, says Topcon, with no adaptation required by the user.
The cost of adding Millimeter GPS to an existing Topcon RTK GPS system is estimated at $12,000, which includes the Lazer Zone transmitter and sensor. Additional rovers working with the same transmitter can be fitted with a sensor for approximately $3,000 each.
