GPS Global Positioning Systems

What Is GPS?

The Global Positioning System, (GPS) is a collection of satellites owned by the U.S. Government that provides highly accurate, worldwide positioning and navigation information, 24 hours a day.

It is comprised of twenty-four NAVSTAR GPS satellites that orbit 12,000 miles above the earth, constantly transmitting the exact time and their position in space. GPS receivers on the earth’s surface record the information received from the satellites. This information is used to determine the accurate location of the receiver.  

GPS uses the triangulation of signals from the satellites to determine locations on earth. By knowing the location of the GPS satellites in space, receivers can determine their distance from a satellite by using the travel time of a radio signal from the satellite to the receiver. After calculating its relative position to at least 3 or 4 satellites, a GPS receiver can, using triangulation, calculate its position.

GPS satellites have four highly accurate atomic clocks on board. They also have a database (or almanac) of the current and expected positions for all of the satellites. When a GPS receiver locates one satellite, it can download all satellite location information and find the remaining needed satellites much more quickly.  

How is GPS used at Public Works?

Spatial accuracy in a Geographic Information System (GIS) is critical. To achieve this in a cost effective and efficient manner, Louisville Metro Public Works utilizes GPS for locating features like signs and guardrails. With the use of computer technology, the spatial information abdout the features are linked to specific attributes, resulting in new spatial data layers for use in a GIS. For example, the spatial location of a stop sign is recorded; additional information about the type of sign, associated roadway, and condition of the sign can also be recorded.