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 centre of mass of the earth).
Anywhere
fix
The ability
of a receiver to start position calculations without being given an approximate
location and time.
Attribute
a characteristic
which describes a Feature. Attributes can be thought of as questions which
are asked about the Feature.
Availability
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.
Back
to Top
--------------------------------------------------------------------------------
- B -
Baseline
A baseline
consists of a pair of stations for which simultaneous GPS data has been
collected.
Base
Station
Also called
a reference station. A receiver that is set up on a known location specifically
to collect data for differentially correcting rover files. The base station
calculates the error for each satellite and, through differential correction,
improves the accuracy of GPS positions collected at unknown locations
by a roving GPS receiver.
bearing
The compass
direction from position to a destination.
Back
to Top
--------------------------------------------------------------------------------
- C -
C/A
code
The standard
(Clear/Acquisition) GPS code; also known as the "civilian code"
or S-code.
Carrier
A radio wave
having at least one characteristic (e.g. frequency, amplitude, phase)
that can be varied from a known reference value by modulation.
Carrier
Phase
GPS measurements
based on the L1 or L2 carrier signal.
Carrier-aided
tracking
A signal
processing strategy that uses the GPS carrier signal to achieve an exact
lock on the pseudo random code. More accurate than standard approach.
Circular
Error Probable (CEP)
A statistical
measure of the horizontal precision. The CEP value is defined as a circle
of a specified radii that encloses 50% of the data points. Thus, half
the data points are within a 2D CEP circle and half are outside the circle.
Clock
bias
The difference
the clock's indicated time and true universal time.
Coarse
Acquisition (C/A)
Code a spread
spectrum direct sequence code that is used primarily by commercial GPS
receivers to determine the range to the transmitting GPS satellite.
Code
phase
GPS measurements
based on the C/A code.
Constellation
Refers to
either the specific set of satellites used in calculating positions or
all the satellites visible to a GPS receiver at one time.
Control
point
Also called
a control station. A monumented point to which coordinates have been,
or are being assigned by the use of surveying observations. The National
Geodetic Survey maintains a nation-wide set of control points.
Control segment A world-wide network of GPS monitoring and control stations
that ensure the accuracy of satellite positions and their clocks.
Course
Made Good (CMG)
The bearing
from your starting point to your present position.
Crosstrack
Error (XTE)
The distance
you are off a desired course in either direction
Cycle
slip
A discontinuity
of an integer number of cycles in the measured carrier beat phase resulting
from a temporary loss-of-lock in the carrier tracking loop of a GPS receiver.
Back
to Top
--------------------------------------------------------------------------------
- D -
Data
message
A 1500 bit
message included in the GPS signal which reports the satellite's location,
clock corrections, and health.
Datalogger
Also called
a data recorder. A handheld, lightweight data entry computer. It can be
used to store additional data obtained by a GPS receiver.
Differential
GPS (DGPS)
a technique
to improve GPS accuracy that uses pseudorange errors measured at a known
location to improve the measurements made by other GPS receivers within
the same general geographic area.
Differential
positioning
Precise measurement
of the relative positions of two receivers tracking the same GPS signals.
Dilution
of Precision (DOP)
an indicator
of satellite geometry for a unique constellation of satellites used to
determine a position. Positions tagged with a higher DOP value generally
constitute poorer measurement results than those tagged with lower DOP.
Dithering
The introduction
of digital noise. This is the process the Department of Defence (DoD)
uses to add inaccuracy to GPS signals to induce Selective Availability.
Doppler-aiding
A signal
processing strategy that uses a measured doppler shift to help the receiver
smoothly track the GPS signal. This allows more precise velocity and position
measurement.
Doppler-shift
The apparent
change in the frequency of a signal caused by the relative motion of the
transmitter and receiver.
Dynamic
positioning
See Kinematic
Positioning.
Back
to Top
--------------------------------------------------------------------------------
- E -
Ephemeris
The predictions
of current satellite position that are transmitted to the user in the
data message.
Ephemeris
Errors
Errors which
originate in the ephemeris data transmitted by a GPS satellite. Ephemeris
errors are removed by differential correction.
Estimated
Time of Arrival (ETA)
The time
of day of your arrival at your destination.
Estimated
Time Enroute (ETE)
The time
left to your destination at your present speed.
Back
to Top
--------------------------------------------------------------------------------
- F -
Federal
Radionavigation Plan (FRP)
Congressionally
managed, joint Department of Defence (DoD) and Department of Transportation
(DOT) effort to reduce the proliferation and overlap of federally funded
radionavigation systems. The FRP is designed to delineate policies and
plans for U.S. government-provided radionavigation services.
Fix
A single
position with latitude, longitude (or grid position), altitude, time,
and date.
Back
to Top
--------------------------------------------------------------------------------
- G -
Geodetic
surveys
Global surveys
done to establish control networks (comprised of reference or control
points) as a basis for accurate land mapping.
GIS
(Geographic Information System)
a computer
based system that is capable of collecting, managing and analysing geographic
spatial data. This capability includes storing and utilizing maps, displaying
the results of data queries and conducting spatial analysis.
Global
Navigation Satellite System (GLONASS)
This is the
Russian counterpart to GPS. GLONASS provides worldwide coverage, however,
its accuracy performance os optimised for the northern latitudes. and
is specified as identical to that of GPS SPS.
Global
Positioning System (GPS)
a system
for providing precise location which is based on data transmitted from
a constellation of 24 satellites
Grid
Also "Coordinate
System". A coordinate system that projects the earth on a flat surface,
using square zones for position measurements.
Ground
Speed
The velocity
you are traveling relative to a ground position.
Back
to Top
--------------------------------------------------------------------------------
- I -
I/O
Abbreviation for Input/Output.
Back
to Top
--------------------------------------------------------------------------------
- K -
Kinematic
positioning
Kinematic
positioning refers to applications in which the position of a non-stationary
object (automobile, ship, bicycle) is determined.
Back to Top
--------------------------------------------------------------------------------
- L -
L1
frequency
1575.42 MHz
GPS carrier frequency which contains only encrypted P code, used primarily
to calculate signal delays caused by the ionosphere.
Latitude
A north/south
measurement of position perpendicular to the earth's polar axis.
L-band
The group
of radio frequencies extending from 390 MHz to 1550 MHz. The GPS carrier
frequencies L1 (15735 MHz) and L2 (1227.6 MHz) are in the L-band.
Longitude
An east/west
measurement of position in relation to the Prime Meridian, an imaginary
circle that passes through the north and south poles.
Back
to Top
--------------------------------------------------------------------------------
- M -
Mask
Angle
The minimum
acceptable satellite elevation above the horizon to avoid blockage of
line-of-sight.
Multi-channel
receiver
A GPS receiver
that can simultaneously track more than one satellite signal.
Multipath
interference
caused by reflected GPS signals arriving at the receiver, typically as
a result of nearby structures or other reflective surfaces.
Multipath
error
Errors caused
by the interference of a signal that has reached the receiver antenna
by two or more different paths. This is usually caused by one path being
bounced or reflected.
Multiplexing
channel
A channel
of a GPS receiver that can be sequenced through a number of satellite
signals.
Back
to Top
--------------------------------------------------------------------------------
- N -
NAVSTAR
The name
given to GPS satellites. NAVSTAR is an acronym for NAVigation Satellite
Timing and Ranging.
Back to Top
--------------------------------------------------------------------------------
- O -
OEM
original
equipment manufacturer.
Back
to Top
--------------------------------------------------------------------------------
- P -
P-code
The Precise
or Protected code. A very long sequence of pseudo-random binary bi phase
modulations on the GPS carrier at a chip rate of 10.23 MHz, which repeats
about every 267 days. Each 1-week segment of this code is unique to one
GPS satellite and is reset each week.
Position
The latitude,
longitude, and altitude of a point. An estimate of error is often associated
with a position.
Positional
Dilution of Precision (PDOP)
Measure of
the geometrical strength of the GPS satellite configuration.
Post-processed
differential GPS
In post-processed
differential GPS the base and roving receivers have no active data link
between them. Instead, each records the satellite observations that will
allow differential correction at a later time. Differential correction
software is used to combine and process the data collected from these
receivers.
Precise
Positioning Service (PPS)
The most
accurate dynamic positioning possible with GPS, based on the dual frequency
P-code.
Pseudo-lite
A ground-based
differential GPS receiver which transmits a signal like that of an actual
GPS satellite, and can be used for ranging.
Pseudo-random
noise (PRN)
A signal
with random noise-like properties. It is very complicated but repeated
pattern of 1's and 0's.
Pseudo-range
A distance
measurement based on the correlation of a satellite transmitted code and
the local receiver's reference code, that has not been corrected for errors
in synchronization between the transmitter's clock and the receiver's
clock.
Back
to Top
--------------------------------------------------------------------------------
- R -
Range
A fixed distance
between two points, such as between a starting and an ending waypoint
or a satellite and a GPS receiver.
Real
Time Kinematic (RTK)
the DGPS
procedure whereby carrier phase corrections are transmitted in real time
from a reference station to the user's roving receiver
Real-time
differential GPS
A base station
which computes, formats, and transmits corrections usually through some
sort of data link (e.g. VHF radio or cellular telephone) with each new
GPS observation. The roving unit requires some sort of data link receiving
equipment to receive the transmitted GPS corrections and get them into
the GPS receiver so they can be applied to its current observations.
Relative
positioning
The determination
of relative positions between two or more receivers which are simultaneously
tracking the same GPS signals.
RINEX
Receiver
INdependent EXchange format. A set of standard definitions and formats
to promote the free exchange of GPS data and facilities the use of data
from any GPS receiver with any software package. The format includes definitions
for three fundamental GOS observable: time, phase, and range.
Rover
Any mobile
GPS receiver collecting data during a field session. The receiver's position
can be computed relative to another, stationary GPS receiver.
Back
to Top
--------------------------------------------------------------------------------
- S -
Satellite
constellation
The arrangement
in space of a set of satellites.
Selective
availability (S/A)
Intentional
degradation of the performance capabilities of the NAVSTAR satellite system
for civilian use by the U.S. military, accomplished by artificially creating
a significant clock error in the satellites.
Space
segment
The space-based
component of the GPS system (i.e. the satellites).
Standard
positioning service (SPS)
The normal
civilian positioning accuracy obtained by using the single frequency C/A
code.
Static
positioning
Location
determination when the receiver's antenna is presumed to be stationary
in the earth. This allows the use of various averaging techniques that
improve the accuracy by factors of over 1000.
Back
to Top
--------------------------------------------------------------------------------
- T -
Track
(TRK)
The direction of movement relative to a ground position.
Back
to Top
--------------------------------------------------------------------------------
- U -
UTC
Universal
Coordinated Time, formerly GMT or Greenwich Mean Time.
Universal
Transverse Mercator (UTM)
A grid coordinate
system that projects global sections onto a flat surface to measure position
in specific zones.
User
segment
The component
of the GPS system that includes the receivers.
Back
to Top
--------------------------------------------------------------------------------
- V -
Velocity
Made Good (VMG)
The speed you are closing in on a destination along a desired course.
Back
to Top
--------------------------------------------------------------------------------
- W -
WAAS
Wide Area
Augmentation System is a FAA funded system of equipment and software that
augments GPS. The WAAS provides a satellite signal for WAAS users to support
enroute and precision approach aircraft navigation.
Back
to Top
--------------------------------------------------------------------------------
- X -
XTE
See "Crosstrack Error"
Back
to Top |
