When Close Isn't Good Enough

The GPS technology used in vehicle navigation is accurate only to within a few yards, which is fine for applications such as those that track truck deliveries. But some situations demand greater precision. For instance, the operators of construction equipment must be extremely accurate in the placement of their blades. A few yards off the mark isn’t acceptable.

For those applications, real-time kinematic (RTK) GPS is used. Here’s how it works for Caterpillar:

Users place a surveyed GPS base station at the construction site. The device looks like a large box with a GPS receiver and a data transmission radio attached. The base station compares its actual surveyed coordinates to the live signals coming from the GPS satellites and then calculates the correction signals to achieve precise location information from the satellites alone. The base station then sends these corrections to the earth-moving equipment’s own GPS systems. It’s done on the fly, allowing the cutting edge of the machine to be in the correct position every second.

“The GPS base station calculates all those errors coming from the atmosphere, the heat, the clouds, etc.,” explains Tom Bucklar, North American region manager for machine control and guidance at Caterpillar. “It builds a correction algorithm, which is sent to the AccuGrade system on the machine to ensure that the blade is positioned within centimeter-level accuracy.”

Copyright © 2007 IDG Communications, Inc.

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