Global positioning system (GPS) is one of the most important modern Navigational Aid. These help us to locate our position to the accuracy of a few hundred meters. All sea going vessels are suppose to have GPS fitted onboard for navigation. Modern navies even use GPS for accurate launching of ballistic and continental missiles. GPS functions using 14 satellites located at different places in the space. An user gets feed from the various satellites in his range and then gives the position after inter relating all the feeds. This is not fully accurate and must not be fully dependant for navigation. We must also do plotting to cross check the position given to us by GPS for errors.
