C-Nav Hardware Reference Guide
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Dynamic Mode when a GPS receiver operates in dynamic mode, it assumes that it is in motion
and certain algorithms for GPS position fixing are enabled in order to calculate a tighter position
fix.
Dynamic Positioning (GPS) is the determination of the position of a moving receiver such as
one mounted on a boat. Generally, each set of coordinates is computed from a single data
sample. The GPS was originally conceived for dynamic positioning of a single receiver,
however, it may be used in a differential mode to increase relative accuracy.
Eccentricity is the ratio of the distance from the center of an ellipse to its focus on the semi-
major axis.
Elevation is the distance above or below Local Vertical Datum.
Elevation Mask the lowest elevation, in degrees, at which a receiver can track a satellite.
Measured from the horizon to zenith, 0º to 90º.
Ellipsoid is a mathematical model approximating the earth’s surface, generated by rotating an
ellipse on its minor axis. GPS positions are computed relative to the WGS-84 ellipsoid. An
ellipsoid has a smooth surface, which does not match the earth’s geoidal surface closely, so
GPS altitude measurements can contain a large vertical error component. Conventionally
surveyed positions usually reference a geoid, which has an undulating surface and
approximates the earth’s surface more closely to minimize altitude errors.
Ephemeris is a tabulation of the positions of all GPS satellites at given points in time.
Epoch is a period of time or a date selected as a point of reference.
Error Ellipse is a statistical measure of the positional error at a given point computed from the
propagation of all errors affecting the position solution and expressed by its semi-major and
semi-minor axis (vectors of greatest and least magnitude) and the covariance (rotation angle in
the reference coordinate system). Two-dimensional errors are typically propagated at one
standard deviation (39.4% probability that the positioning lies on or within the ellipse) or 2.1447
times the standard deviation (95% confidence) level.
European Geostationary Navigation Overlay Service (EGNOS) a European satellite system
used to augment the two military satellite navigation systems now operating, the US GPS and
Russian GLONASS systems.
Fractional Instantaneous Phase Measurement is a measurement of the carrier beat phase that
does not include any integer cycle count.
Frequency Band is a range of frequencies in a region of the electromagnetic spectrum.
Frequency Spectrum is the distribution of signal amplitudes as a function of frequency of the
constituent signal waves.
Galileo is the navigation satellite system currently being developed and implemented by the
European Space Agency, the European Union. Initial operation is planned for 2008.
Geodetic Leveling Network is a network of vertical control or benchmarks whose heights are
known as accurately as possible, and whose horizontal position is known only approximately.
Geoid is the gravity-equipotential surface that best approximates mean sea level over the entire
surface of the earth. The surface of a geoid is too irregular to use for GPS readings, which are
measured relative to an ellipsoid. Conventionally surveyed positions reference a geoid.
Calculating the distance between the geoid and ellipsoid at each position and subtracting this
from the GPS altitude measurement can obtain more accurate GPS readings.
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