GPS-20A Chapter 1
Installation Manual Overview
92621632-06 1-1
Chapter 1 Overview
1.1 GPS
1.1.1 GPS satellite alignment
GPS (Global Positioning System) is a position measuring system that uses 4 satellites for each of 6
orbits (3 spare), with durations of 11 hours 58 minutes, orbiting approximately 20,000km above the
earth.
1.1.2 GPS configuration
GPS is based on the principle of calculating the distance of 3 or more satellites from the user and
deriving the user’s position. The intersect point of the orbital trajectories becomes the current
measured position (latitude, longitude, altitude).
1.2 SBAS (WAAS, EGNOS, MSAS)
SBAS is a robust system designed to greatly improve the accuracy of GPS positioning using
geo-stationary satellites currently being produced in the US, Europe and Japan. There are 3 types of
systems being produced, WAAS in the US, EGNOS in Europe and MSAS in Japan. WAAS and
EGNOS are currently going through application testing and transmit position correction data at the
same frequency as GPS satellites. Because position correction data is transmitted from geo-stationary
satellites, it is possible to receive position correction data anywhere in the world. However, due to the
fact that these geo-stationary satellites are still going through application testing, the quality of the
position correction data may be degraded without notice.
1.3 Equipment outline
The GPS-20A is a high performance GPS receiver module containing an 18-channel parallel receiver
sensor, which is ready for the SBAS service. By simply connecting a power supply to the GPS-20A,
highly accurate position data can be quickly supplied to a Plotter or the ship’s navigation devices. The
GPS-20A is also compatible with differential correction service broadcast from conventional beacon
stations.
1.4 Application standard
The GPS-20A conforms to the General Requirements of Maritime Navigation and
Radiocommunication Equipment and Systems, IEC 60945 (Ed.3).
1.5 Software specification
PN-012
Caution
GPS uses the (World Geodetic System) coordinate system. On previous global maps,
each zone used a different coordinate system.
However, by using the WGS system
where all zones are unified to one coordinate system, the latitude and longitude are
used in positioning. Therefore, when using a map that uses a different coordinate
system, the map lat/lon may be different to the lat/lon displayed on the navigation unit.
