NavCom Technology GPS Products, User Manual

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SF-2050 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-56