Surveying with GPS 1

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GPS can be used as a surveying tool as well as a positioning tool.

When surveying with GPS, rather than the absolute positions of the points being measured, the baseline (three-dimensional distance) between two points is computed instead.

The answer is generally not instantaneous. GPS data has to be simultaneously collected at both points and used later in computations to determine the baseline. This is generally known as Static GPS.

Some systems compute the baseline in real time to give an almost instantaneous answer. This technique is generally known as Real-Time Kinematic (RTK) GPS.

The measurement of the baseline between the two points can be very accurate (cm level and better). This relative positioning of points with respect to each other is much more accurate than instant absolute positioning using one receiver.

At least two receivers are required. To get accurate absolute positions one receiver has to be on a known point. The Ordnance Survey active GPS Network provides a network of GPS receivers on known points that can be used for surveying with GPS.

The amount of data needed increases with baseline length and required accuracy.