What is gps?

[hassen1]

GPS is a satellite-based radionavigation system developed and operated by the U.S. Department of Defense (DOD). GPS permits land, sea, and airborne users to determine their three-dimensional position, velocity, and time 24 hours a day, in all weather, anywhere in the world with a precision and accuracy far better than other radionavigation systems available today or in the foreseeable future.

GPS consists of three segments: space, control, and user.

The Space Segment, consists of a minimum of 24 operational satellites in six circular orbits 20,200 km (10,900 NM) above the earth at an inclination angle of 55 degrees with a 12 hour period. The satellites are spaced in orbit so that at any time a minimum of 6 satellites will be in view to users anywhere in the world. The satellites continuously broadcast position and time data to users throughout the world.

The Control Segment consists of a master control station in Colorado Springs, with five monitor stations and three ground antennas located throughout the world. The monitor stations track all GPS satellites in view and collect ranging information from the satellite broadcasts. The monitor stations send the information they collect from each of the satellites back to the master control station, which computes extremely precise satellite orbits. The information is then formatted into updated navigation messages for each satellite. The updated information is transmitted to each satellite via the ground antennas, which also transmit and receive satellite control and monitoring signals.

The User Segment consists of the receivers, processors, and antennas that allow land, sea, or airborne operators to receive the GPS satellite broadcasts and compute their precise position, velocity and time.
The GPS concept of operation is based upon satellite ranging. Users figure their position on the earth by measuring their distance from the group of satellites in space. The satellites act as precise reference points.

Each GPS satellite transmits an accurate position and time signal. The user's receiver measures the time delay for the signal to reach the receiver, which is the direct measure of the apparent range to the satellite. Measurements collected simultaneously from four satellites are processed to solve for the three dimensions of position, velocity and time

[pussykitty]

hohoho, this is a very good explanation, very informative, thansk hassen

[rowenahere]

Many positioning systems were developed, but had their own drawbacks:

Landmarks/Seamarks/Daymarks, works only in local areas, subject to movement/destruction by environmental factors.

Example:lighthouse.

Dead Reckoning, method to estimate an object's position based on distance it traveled from previous location to current one. Highly complicated, unskilled tools used, inaccurate results, used in ships, aircrafts, vehicles, trains etc.

Example lakes.


Celestial: Complicated, works only at night with low accuracy.

Example observing zodiac signs.

[rowenahere]

In continuation to above post:

OMEGA, first truly "global radio navigation system" for aircraft, developed by United States Navy, had capabilities to cover oceans worldwide with a four mile accuracy for setting up positions. Due to GPSs’ popularity, used only in United States for submarines.

LORAN (LOng RAnge Navigation), originally, "LRN" (Loomis radio navigation), after physicist Alfred Lee Loomis, its inventor, during World War II and used by US Navy and Royal Navy. Losing popularity to GPS, as coverage is limited (coastal), accuracy affected by geographic factors, easy to jam.

SatNav (Satellite navigation system), originally for military applications, provides autonomous geo-spatial positioning with global coverage, based on low-frequency doppler measurements, thus sensitive to small movements at receiver and updates are less due to few satellites.