GPS

In the ancient period, several techniques of navigation were practiced by the people. Some of them were namely land and air, current and wind, sun and star, bird and wave, etc. In earlier days navigating by stars was practiced most often. But this technique was not as accurate as it should be, because it required the nights to be clear and also one has to be very precise while taking the measurements. Since no better technology was available at that time, to find the correct location of objects, this ancient technique continued to be used for centuries.

Location data is an information about the geographic positions of devices such as (smartphones, tablets, etc.) or structures (such as buildings, monuments, etc.) The geographic positions of location data are called coordinates, they are commonly expressed in Latitude and Longitude format. Additional attributes such as elevation or altitude may be included and helps data users get more accurate picture of the geographic positions of their data.

What is GPS?

GPS stands for Global Positioning System and it came into existence with an intention to serve the military purposes.GPS is actually a satellite navigation system that is space-based and is capable of providing location and time information in all climatic conditions. Initially it was named as NAVSTAR GPS(Navigation Satellite Timing And Ranging Global Positioning System). The first satellite was launched in 1978 and GPS became quite functional in the USA in 1995. The system comprises of near about thirty satellites which are working in harmony with each other and are termed as satellite constellation. Until the year 2000 the highest quality signals were used only for military purposes, but later it was made available for all the civilians at absolutely no cost. At present GPS is managed by the US Airforce.

How does GPS work?

Now that you already know what GPS is, But have you ever wondered how it works to calculate your position. In its most basic form GPS triangulates your position, by measuring how far it is from different satellites. It knows the position of each satellite and by drawing an imaginary ring around each one it can calculate its position as the point where all the rings intersect.

GPS is a system which majorly comprises of three distinct components i.e. satellites, receivers and ground stations. Satellites act like the stars in constellation and we know where they are supposed to be at any given time. In order to ensure that the satellites are exactly where we think they are, the ground stations use radar. Receiver is constantly listening to a signal from the satellites. The receiver tries to understand at what distance they are from few of these satellites. Once the receiver is done with calculating its distance from four or more satellites, it knows  your exact location. Doesn’t matter where you are on the planet, you will be in the line of sight of a minimum of four GPS satellites at any point in time. Every single satellite pass on information regarding its location and recent time at consistent intervals. These signals traveling at the speed of light are intercepted by your GPS receiver which then calculates how far each satellite is by keeping track of the time required for the messages to reach its destination.

To understand it in more subtle form, imagine you are standing somewhere on the earth with three satellites namely A, B and C in the airspace. In case you know at what distance you are from satellite A then you can assume that you are located at some point on the circle drawn with the help of satellite A.If you practice the same procedure for the other two satellites i.e satellite B and satellite C, then you can surely get your location by observing the point at which the three circles meet. This same concept is used by the GPS receiver but instead of circles uses overlapping spheres. The more satellites there are above the horizon, the more accurately your GPS  unit can determine where you are. This process is called trilateration.

If the GPS receiver knows the exact time, then it can surely determine the time of arrival of  GPS signals. The task of maintaining the exact time is usually done by the atomic clocks, but they are quite expensive and also due to certain other reasons they can not be installed in each and every GPS receiver. So to tackle this challenge, the GPS signal associated with the fourth satellite plays a key role, since it discards the use of atomic clocks to solve the equation that could possibly give the correct time. You can detect your location even in the case, where only three satellites are in a position to send signals to the receiver, but there is a probability that location detected in such a scenario might not be that perfect. So to get the perfect location the receiver must be able to get signals from four different satellites which can give your location in three dimensions i.e east, north and altitude. In the case of the availability of signals from only three satellites as mentioned above, the approximate position is calculated in the same way as it is done if a person or object is at MSL(mean sea level). If you are genuinely at MSL, the obtained location will undoubtedly be accurate. It is possible for a contemporary GPS receiver to track all the satellites that are within its reach at the same time but will make use of only a few of them to determine your location.

Applications of GPS

Global positioning systems are being used in every aspect of our lives today. These systems have revolutionised technology by becoming more interactive and useful. Also, they are extremely versatile providing help in navigating unfamiliar cities, locating missing people, mapping forests and helping farmers harvest their fields.GPS navigation and google maps have revolutionised the ease with which we can travel, whether it be by car, boat, plane, train or foot.GPS has changed the way we live and they have also changed the way we fight.GPS has revolutionised military operations. The accuracy, security and reliability of military GPS give a nation and its allied forces an asymmetric advantage over the enemy .This advantage allows the soldiers, sailors, marines and airmen to accomplish more with smaller forces than was ever possible before.

NAVIC (Navigation with Indian Constellation) is India’s own indigenous global navigation satellite system. It is designed to provide accurate positioning information service to Indian users and users in the region extending up to 1500km from its boundary.