|
A B
C D
E F
G H
I J
K L
M N
O P
Q R
S T
U V
W X
Y Z
|
| Absolute Positioning |
Positioning mode in which a position is identified with respect
to a well-defined coordinate system, commonly a geocentric system
(i.e., a system whose point of origin coincides with the center
of mass of the earth). |
| Accuracy |
The degree of conformance between the estimated or measured
position, time, and/or velocity of a GPS receiver and its true
time, position, and/or velocity as compared with a constant
standard. Radionavigation system accuracy is usually presented
as a statistical measure of system error and is characterized
as follows: Predictable
- The accuracy of a radionavigation system's position solution
with respect to the charted solution. Both the position solution
and the chart must be based upon the same geodetic datum.
Repeatable - The accuracy
with which a user can return to a position whose coordinates
have been measured at a previous time with the same navigation
system.
Relative - The accuracy
with which a user can measure position relative to that of
another user of the same navigation system at the same time. |
| Acquisition Time |
Amount of time required for a GPS unit to lock onto 3 satellites
to provide a "2D View" of present position. |
| Almanac |
Orbit information for all the satellites, including clock
correction, and atmospheric delay parameters. This data is used
to facilitate rapid SV acquisition. The orbit information is
a subset of the ephemeris data with reduced accuracy. Information
on the entire GPS constellation is transmitted by each GPS satellite. |
| Ambiguity |
The unknown number of complete wavelengths (cycles) of the
carrier phase contained in a measurement between a single satellite
and a single receiver. |
| Analog |
A type of transmission characterized by variable waveforms
representing information, contrasted with digital. A standard
clock with moving hands is an analog device, whereas a clock
with displayed and changing numbers is a digital device. The
human voice and audible sounds are analog. Modern computers
are invariably digital, but when they communicate over telephone
lines, their signals must be converted to analog using a modem
( a modulator/demodulator). The analog signal is converted back
into a digital form before delivering it to a destination computer. |
| Anywhere fix |
The ability of a receiver to start position calculations
without being given an approximate location and time. |
| Application software |
These programs accomplish the specialized tasks of the user,
while operating system software allows the computer to work.
A computer-aided dispatch system is application software, as
is each word processing program. |
| Ascending node |
The point at which an object's orbit crosses the reference
plane (e.g. Equatorial plane) from South to North. |
| Automatic Vehicle Location - AVL |
A type of system using any sort of technology to track or
locate a vehicle. |
| Availability |
The availability of a navigation system is the percentage
of time that the services are usable. Availability is an indication
of the ability of the system to provide usable service within
the specified coverage area. Signal availability is the percentage
of time that navigational signals transmitted from external
sources are available for use. Availability is the percentage
of time that navigational signals transmitted from external
sources are available for use. Availability is a function of
both the physical characteristics of the environment and the
technical capabilities of the transmitter facilities. The number
of hours per day that a particular location has sufficient satellites
(above the specified elevation angle and less than the specified
PDOP value) to make a GPS position fix |
| Azimuth |
A horizontal direction expressed as an angle between a fixed
direction, and the direction of the object. The fixed direction
in normally North. |
|
A B
C D
E F
G H
I J
K L
M N
O P
Q R
S T
U V
W X
Y Z
|