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7 The GlobAl PoSITIonInG SYSTem
The Global Positioning System (GPS) is a constellation of satellites that orbit the earth twice a day,
transmitting precise time and positioning information to anywhere on the globe, 24 hours a day.
The system was designed and deployed by the U.S. Department of Defense to provide continuous,
worldwide positioning and navigation data to U.S. and allied military forces. GPS broad commercial
applications were recognized early in the system's development, and the U.S. government decided
to allow free access to GPS signals. Today, GPS is used in a wide variety of commercial and scientific
applications.
7.1 GPS PAGe
The GPS page shows GPS data in graphic mode, displaying satellite availability and status.
> 'MENU' 1 sec. + "GPS PAGE" + 'ENT'
This page displays the current status and location of all available satellites in the GPS constellation,
referenced to the initial position or last fix.
On the bottom half of the screen (see previous figure) there is a polar representation of the Azimuth
and Elevation of the satellites used to compute a position fix.
The Elevation is the height of the satellite above the horizon, with 5° (lowest) near the horizon and
90° (highest) being directly overhead (the Geopilot II Plus does not normally use satellites with
Elevations lower than 10°). Azimuth is the satellite's location in relation to true north, measured
clockwise as a bearing. A satellite with an Azimuth of 90° is to the east.
The circle contains a number indicating the number of the satellite and it is green when it is used for
the fix solution (red otherwise). On the left side there are histograms indicating the S/N ratio (SNR).
The bar is green when the satellite is used for the fix (red otherwise). When a valid fix is received,
the Geopilot II Plus displays the current position coordinates, Date, Time, HDOP , VDOP ,GS, TRK
and ALT on the GPS page.
7.2 GPS reCeIver SPeCIfICATIonS
• receiver:
• Channels:
• max Solution Update rate: 10 sec.
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Fig. 7.1 - The GPS page
L1, C/A code, DGPS/WAAS Ready
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