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receive all satellites unambiguously and to give some resistance to noise and
multipath.
TIME TO FIRST FIX (TTFF)
The time it takes to find the satellites is called the Time to First Fix (TTFF). If you have
not used your GPS unit for several months, the almanac data for the satellites may be
out of date. The unit is capable of recollecting this information on its own, but the
process can take several minutes. The time it takes after the user first turns on the
GPS receiver, when a GPS receiver has lost memory, or has been moved over 300
miles from its last location.
TRIANGULATION
A method of determining the location of an unknown point, as in GPS navigation, by
using the laws of plane trigonometry.
Universal Time Coordinated (UTC)
UTC is the time as maintained by the U.S. Naval Observatory. Because of variations in
the Earth's rotation, UTC is sometimes adjusted by an integer second. The
accumulation of these adjustments compared to GPS time, which runs continuously,
has resulted in an offset between GPS time and UTC. After accounting for leap seconds
and using adjustments contained in the navigation message, GPS time can be related
to UTC within 20 nanoseconds or better. Greenwich Mean Time (GMT) is still the
standard time zone for the prime meridian (zero longitude).
Warm Start
Start mode of the GPS receiver when current position, clock offset and approximate
GPA time are input by user or by the application software. Almanac is retained, but
ephemeris data is clear.
Wide Area Augmentation System (WAAS)
Developed by the United States government, WAAS is a Satellite-Based Augmentation
System (SBAS) that calculates the errors in the GPS signal at several monitoring
stations around the country, then transmits error correction messages from
geostationary satellites to GPS receivers.
World Geodetic System 1984 (WGS 84)
The primary map datum used by GPS. Secondary datums are computed as differences
from the WGS 84 standard. WGS 84 is a set of U.S. Defense Mapping Agency (DMA)
parameters for determining global geometric and physical geodetic relationships.
Parameters include a geocentric reference ellipsoid; a coordinate system; and a
