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K GPS Glossary of Terms
MiLLennium GPSCard SW Version 4.503/4.52 Command Descriptions Manual Rev 2 269
Dilution of A numerical value expressing the confidence factor of the position solution
Precision (DOP) based on current satellite geometry. The lower the value, the greater the confidence in
the solution. DOP can be expressed in the following forms.
GDOP - uncertainty of all parameters (latitude, longitude, height, clock offset)
PDOP - uncertainty of 3D parameters (latitude, longitude, height)
HTDOP - uncertainty of 2D and time parameters (latitude, longitude, time)
HDOP - uncertainty of 2D parameters (latitude, longitude)
VDOP - uncertainty of height parameter
TDOP - uncertainty of clock offset parameter
Doppler The change in frequency of sound, light or other wave caused by movement of its source
relative to the observer.
Doppler Aiding A signal processing strategy, which uses a measured Doppler shift to help a receiver
smoothly track the GPS signal, to allow more precise velocity and position
measurement.
Double-Difference A mathematical technique comparing observations by differencing between receiver
channels and then between the reference and rover receivers.
Double-Difference Carrier phase ambiguities which are differenced between receiver channels
Carrier Phase and between the reference and rover receivers. They are estimated when
Ambiguity a double-difference mechanism is used for carrier phase positioning. (Sometimes
double-difference ambiguity or ambiguity, for short)
Earth-Centred This is a coordinate-ordinate system which has the X-coordinate in the
Earth-Fixed (ECEF) earth’s equatorial plane pointing to the Greenwich prime meridian, the Z-axis pointing
to the north pole, and the Y-axis in the equatorial plane 90° from the X-axis with an
orientation which forms a right-handed XYZ system.
Elevation The angle from the horizon to the observed position of a satellite.
Ellipsoid A smooth mathematical surface which represents the earth’s shape and very closely
approximates the geoid. It is used as a reference surface for geodetic surveys, refer to the
RTKA/B log on Page 207.
Ellipsoidal Height Height above a defined ellipsoid approximating the surface of the earth.
Ephemeris A set of satellite orbit parameters that are used by a GPS receiver to calculate precise
GPS satellite positions and velocities. The ephemeris is used in the determination of the
navigation solution and is updated periodically by the satellite to maintain the accuracy
of GPS receivers.
Ephemeris Data The data downlinked by a GPS satellite describing its own orbital position with respect
to time.
Epoch Strictly a specific point in time. Typically when an observation is made.
Field A character or string of characters immediately preceded by a field delimiter.
Fixed Ambiguity Carrier phase ambiguity estimates which are set to a given number and held
Estimates constant. Usually they are set to integers or values derived from linear combinations of
integers.
Fixed Discrete Carrier phase ambiguities which are set to values which are members of a
Ambiguity predetermined set of discrete possibilities, and then held constant.
Estimates
Fixed Field A field in which the number of characters is fixed. For data fields, such fields are shown
in the sentence definitions with no decimal point. Other fields which fall into this
category are the address field and the checksum field (if present).
Fixed Integer Carrier phase ambiguities which are set to integer values and then held