Ephemeris (Ephemeris Error): Predicted changes in satellite orbit used by the GPS device to lock on to new satellite triangulations. Typically there are errors in these predictions that are removed by differential corrections.
Geo-fencing: Designates a geographic perimeter in which a vehicle should operate; an alert is issued if the vehicle travels beyond the borders of a geo-fence.
Geographic Information System (GIS): Combines positional GPS data with other descriptive mapping information to form a layered map displaying other data relational to vehicle location-e.g., landmarks, weather patterns.
Global Positioning System (GPS): Refers to a series of navigational satellites that make it possible to precisely pinpoint the latitude and longitude of a receiver.
GPS Fleet Tracking System: A network of devices that make it possible to locate vehicles precisely using satellites, and gather information about those vehicles that can be used to analyze their movements.
Assisted GPS: A way to improve lock time (see below) by triangulating position in relation to historical data and cell-tower locations.
Lock: The time needed for a GPS receiver on the ground to receive information from up to three satellites to compute its geographical location. This can take time, particularly in moving vehicles. There are three approaches to handling lock "start":
Hot Start: The GPS device "remembers" its last location and attempts to lock into the same satellites to calculate a new position based upon previous information. This is the quickest approach, but only if there hasn't been much distance traveled since the last reading.
Warm Start: The GPS device "remembers" its last location, but resets with new satellite readings. This takes a little longer but is more accurate.
Cold Start: A fresh recalculation. Previous information is deleted and current position is recalculated. Takes the longest.
Multipath: Interference signals from multiple transmissions-minimized by low-on-the-horizon satellites.
Satellite Constellation: The group of satellites, usually three or more, employed to determine geographic position.
Static Positioning: The process of averaging multiple GPS positions taken successively over time with a stationary antenna to increase accuracy.