NavCom SF-2040 Rev.F - Manual (Page 84)

SF-2040 User Guide – Rev. F
GAGAN (GPS Aided Geo Augmented Navigation)
an Indian satellite system that provides a set of
corrections for the GPS satellites, which are valid for
the Indian region. They incorporate satellite orbit and
clock corrections.
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.
Global Positioning System (GPS) geometrically,
there can only be one point in space, which is the
correct distance from each of four known points. GPS
measures the distance from a point to at least four
satellites from a constellation of 24 NAVSTAR
satellites orbiting the earth at a very high altitude.
These distances are used to calculate the point’s
position.
GMT see Greenwich Mean Time.
GPS see Global Positioning System.
GPS time a measure of time. GPS time is based on
UTC, but does not add periodic ‘leap seconds’ to
Glossary-82