User`s guide

Appendix
Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05
202
Dynamic Positioning
Determination of a timed series of sets of coordinates for a moving receiver, each set of
coordinates being determined from a single data sample, and usually computed in real
time.
Earth-Centered Earth-Fixed (ECEF)
Usually refers to a coordinate system centered at the center of the earth that rotates with
the earth. Cartesian coordinate system where the X direction is the intersection of the
prime meridian (Greenwich) with the equator. The X and Y vectors rotate with the earth.
Z is the direction of the spin axis.
Eccentric Anomaly 'E'
The regularizing variable in the two-body problem. E is related to the mean anomaly M by
Kepler's equation. M = E esin(E), where e is the eccentricity.
Eccentricity 'e'
The ratio of the distance from the center of an ellipse to its focus to the semi-major axis. e
= (1 - b2/a2) 1/2, where a and b are the semi-major and semi-minor axes of the ellipse.
Ecliptic
The earth-sun orbital plane. North is the direction of the system's angular momentum.
Also called the ecliptic pole.
Elevation
Height above mean sea level or vertical distance above the reference geoid.
Elevation Mask Angle
The elevation angle below which satellites are ignored. Normally set to ten degrees to
avoid interference problems caused by buildings, trees, multi-path, and atmospheric
errors.
Ellipsoid Height
The measure of vertical distance above the ellipsoid. Not the same as elevation above
sea level, because the ellipsoid does not agree exactly with the geoid. GPS receivers
output position fix height referenced to the WGS-84 datum.
Ephemeris
A list of orbital parameters of a celestial object that can be used to compute accurate
positions as a function of time. Available as broadcast ephemeris or as post-processed
precise ephemeris.
Epoch
Measurement interval or data frequency. For example, if measurements are made and
reported every five seconds, then we have five second epochs.
Fast Switching Channel
A switching channel with a sequence time short enough to recover (through software
prediction) the integer part of the carrier beat phase.