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In concert with the Millimeter GPS, Barnhill used Topcon PZL-1 lasers to create a Lazer Zone - a rotating (600 rpm) signal that fans out to a height of 33 feet, creating a “wall of laser light,” Collins says. With Lazer Zone, the resulting integrated system can generate vertical accuracy within a few millimeters, compared to centimeter-level vertical accuracy using conventional RTK GPS systems.

On the airport project, Barnhill was able to set the Millimeter GPS system up quickly, using four Lazer Zone transmitters; one receiver with a LazerZone sensor mounted on a mast attached to the toe arm of each of the four pavers; and two rover receivers each 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 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).

The milling operation started at 8 pm on October 2, 2007, with four machines, explains Mark Eakes, GPS manager for Barnhill. After the milling machines got far enough ahead, the pavers were positioned on the runway.

They used two Topcon PZL-1 lasers on one side and two pavers on the other side, staggered about 20 feet apart, so they could receive the correction signals from the lasers. Following behind one of the pavers in each set, a Topcon HiPer Lite was used to check the grade. Barnhill’s first pass created the centerline crown and paving crews worked outward from that point.