NavCom RT-3010 Rev.E - Manual (Page 52)

RT-3010 User Guide - Rev. E
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 a mathematical figure 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.
epoch literally a period of time. This period of time is
defined by the length of the said period.
geoid 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 . More accurate GPS readings can be obtained by
calculating the distance between the geoid and
ellipsoid at each position and subtracting this from the
GPS altitude measurement.
GIS (Geographical Information Systems) a computer
system capable of assembling, storing, manipulating,
updating, analyzing and displaying geographically
referenced information, i.e. data identified according to
their locations. GIS technology can be used for scientific
investigations, resource management, and
development planning. GIS software is used to display,
edit, query and analyze all the graphical objects and
their associated information.
Glossary -50