Flatirons, Inc.

The Global Positioning System is a system of satellites established and maintained by the United States Department of Defense. These satellites can be used by civilians for a variety of tasks ranging from navigation and mapping to high precision Geodetic Surveying. One of the largest groups of civilians using the GPS is the land surveying community, as it provides an efficient means for gathering information that in the past would have taken many days to gather.

Beginning in the early 1980's, the U.S. Department of Defense began to deploy a system of satellites intended for U.S. military use to obtain accurate navigational & positional locations. These satellites broadcast a coded signal, and with the proper receiver unit, air, water & ground units could receive highly accurate information about their geographical location. Receivers currently available to the public allow for navigation, but not for real-time precise positioning.

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There are currently several levels of GPS units available to the general public, varying by accuracy and cost of the unit :

Navigational Units

Small hand held units at relatively low cost allow boaters and hikers to know their position within a few hundred meters. This accuracy is sufficient for recreational use.

Mapping

A hand held or similar unit at mid-range price that is linked to a fixed broadcast base station. These units allow utility companies, municipalities and others to locate various items (telephone poles, waterlines, valves) with a positional tolerance of several meters. This is suitable for some Geographical Information Systems (GIS) mapping purposes.

Real Time Kinematic

Roving, high precision units available at relatively high cost that are linked by radio to a fixed base station, allowing quick on-site gathering of data without the need for post-processing. These units are suitable for topographic mapping, construction layout, and other uses with a positional tolerance of centimeters.

Geodetic

For highly precise measuring of long baselines, or measuring between points in difficult terrain (across rivers, mountain, urban). These units use long observation times and off site post processing of data to obtain a sub-centimeter positional tolerance.

Flatirons, Inc. currently uses geodetic GPS units to perform high precision, long baseline surveys, and RTK units to gather precise data in real time. Availability of other equipment can be arranged if it is appropriate for a particular task.

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Global Positioning Systems Overview from The Geographer's Craft

U.S. Coast Guard Navigation Center

NAVSTAR signal characteristics

Iowa State and S. Wormley's GPS Rescources