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.  

Along with the entire collection of satellites, the Iowa Department of Transportation as implemented a network around the state with GPS base stations.  These stations constantly gather information and are transmitted to survey accurate GPS units, via the internet or thru cellular communication, to increase location accuracy to centimeters.  This system not only enhances the survey collection but also that of agriculture guidance and truck or fleet monitoring.

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, Fort Dodge Public Works utilizes GPS for locating features like signs. With the use of computer technology, the spatial information about 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.
In the Engineering Division of Public Works, GPS is used for the collection of survey data, topography, property information, and the accurate mapping of infrastructure, such as sewer manholes, intakes and fire hydrants.
All of this data can also be linked to other spatial data, and a system for all aspects of planning and monitoring is created.

Contact Us

David M. Odor, GIS Specialist
819 1st Ave S
Fort Dodge, IA 50501
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