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Environmental factors that influence the position accuracy and TTFF including such
as
tall buildings,
narrow street and passageway,
protection film on glass,
heavy foliage,
large cliffs,
and other obstructions where the satellite signals may blocked, and, poor satellites
geometry situation. Initial state of the receiver, means latest status in memory of
the receiver, may mainly determine the time of TTFF. Position can be quickly fixed
within only 10 seconds from a hot-start state and needs 60 seconds typically from a
cold-start state. Or, might need at least 3 to 5 minutes from a completely
restart-state, for example, flying a distance over 500 kilometers from initial origin.
BTGPS III uses the satellite signals to calculate an exact geodetic location through
triangulation method, contained in 7 meters CEP accurateness devoid of Selective
Availability (SA), which is good enough for general location awareness purposes.
The position data is then converted within the receiver to latitude and longitude
coordinates, which is usually provided in the geodetic datum on which GPS is based
(WGS 84). Position offsets of hundreds of meters or much more can result from
using the wrong datum.
In addition to datum used, there are number of positioning errors can occur,
limiting accuracy. The major errors including satellites orbiting error, poor satellites
geometry, multi-path signals, atmospheric delay and receiver clock timing.
The indication of GPS signal reception is described in section “Indication of BTGPS
III operation” of Chapter 3.
