C-Nav IALA Hardware Reference Manual page 94

C-Nav Hardware Reference Guide
Geoidal Height is the undulation of the geoid above or below the reference ellipsoid.
Geographical Information System (GIS) is 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 (approximately 20,200km). These distances are used to calculate the point's
position.
GPS Aided Geo Augmented Navigation (GAGAN) is 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.
GPS Time is a measure of time. GPS time is based on UTC, but does not add periodic 'leap
seconds' to correct for changes in the earth's period of rotation. As of April 2008 GPS time is 14
seconds ahead of UTC.
Greenwich Mean Time (GMT) is the local time of the 0° meridian passing through Greenwich,
England.
Handover Word is the word in the GPS message that contains time synchronization
information for the transfer from the C/A-code to the P-code.
Horizontal Geodetic Network is a network for which the horizontal, coordinate, latitude, and
longitude of the control points in the network are determined as accurately as possible, and
heights are known only approximately.
Independent Baseline those baselines that provide a unique position solution for a given
station.
Integer-cycle Ambiguity is the unknown number of whole carrier cycles between the satellite
and the receiver.
Ionosphere is the region of the earth's atmosphere between the stratosphere and the
exosphere approximately 50 to 250 miles above the earth's surface
Ionospheric Refraction Delay is a delay in the propagation of the GPS signal caused by the
signal traveling through the ionosphere.
Issue of Data, Clock (IODC) indicates the issue number of the data set and thereby provides
the user with a convenient means of detecting any change in the correction parameters. The
transmitted IODC will be different from any value transmitted by the satellite during the
preceding seven days.
Kalman Filtering is a linear system in which the mean squared error between the desired
output and the actual output is minimized when the input is a random signal generated by white
noise. The Kalman filter looks at a target to remove the effects of the noise and get a good
estimate of the location of the target at the present time (filtering), at a future time (prediction),
or at a time in the past (interpolation or smoothing). The Kalman filter is a recursive estimator
with two phases: predict and update. The predict phase uses the estimate from a previous state
to produce an estimate of the current state. The update phase uses the current state
measurements to arrive at a new more accurate estimate.
94