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09/25/02 GPS_field_guide 8:19 A9/P9
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GLOSSARY
Accuracy : How close to the real value a measurement is.
Backlight: Selectable on/off illumination that lights the display for enhanced screen at
night and in low light.
Contrast: The difference between the lightest and darkest areas on a display screen.
Coordinates : The unique description of a geographic position using numeric
characters.
Dilution of Precision (DOP): The dilution of precision (DOP) is an indication of the
quality of the results that can be expected from a GPS point position. It is a
measure based solely on the geometry of the satellites in the sky.
Ephemeris: The predictions of current satellite position that are transmitted to the
user in the data message.
Initialization: Refers to the procedure of telling a GPS receiver where it is, when it is
turned on for the first time. Information required for initialization includes
approximate present position in latitude/longitude coordinates, the current local
time and date (information obtained through the satellite signal when using the
eTrex unit).
Map Datums: Since the Earth is not flat a model needs to be used in order for the
GPS receiver to give the coordinates. These models are calls Datums.
Multipath: Mutipath is the phenomena by which the GPS signal is reflected by some
object or surface before being detected by the receptor antenna creating
multipath for a same signal that results in a calculation error when estimating
the distance between the satellite and the receiver
Position: A geographic location on the earth, commonly measured in latitude and
longitude.
Satellite constellation: The arrangement in space of a set of satellites.
Segment: One of several parts or pieces that fit with others to constitute a whole
object.
GPS Control segment: A Master Control Station and a number of monitoring
stations around the world that ensure the accuracy of satellite positions and their
clocks.
GPS Space segment: The network of 24 GPS satellites.
GPS User segment: The receivers of GPS signals such as your eTrex Unit.