basic of gps

What is GPS?
Simply put, Global Positioning System or GPS, is a technology that can give your accurate position anywhere on earth (latitude/longitude). You need a special GPS receiver that can receive signals from satellites.
Does it work in India? What are the problems faced by GPS users in India?
Yes. It works anywhere on the planet where you can receive signals from the satellite. You will need a pretty clear view of the sky for GPS to work, so it won't work inside buildings, underground or even in a forest. Few years back, GPS wasn't available to it's full accuracy, but since the year 2000 it is available with full accuracy anywhere in the world and to anyone who buys a GPS receiver.
Who owns this system?
The Global Positioning System is owned and operated by United States Department of Defence. But it is available freely to anyone in the world for use. Other countries have developed similar Satellite Navigation Systems of their own. For example, European Union is developing a system called Galileo and Russia has an operational system called GLONASS. Many modern receivers are capable of using signals from all these systems.
Can civilians use GPS?
Yes it is allowed for civilian use, with no restriction. There are two kind of GPS signals,
C/A code: which is the civilian signals and given acuracy about 8-15m
P code - which is military signal and only US military can use that, which is more accurate.
There are high-end civilian receivers available, called dual-frequency receivers, which uses part of P-code, not the full signal, and gives higher accuracy than single frequency receivers.
Is there a fee for using GPS?
GPS is free for use. There is no subscription or monthly fees to pay. You need to buy a receiver that is capable of receiving the signals. But if you want to use add-on services like, differential correction for better accuracy, there may be additional fee.
Do WAAS ( Wide Area Augmentation System ) enabled GPS receivers work in India?
Unfortunately No. WAAS is a US specific system and users cannot receive WAAS signals in India. The receiver will continue to work, but without WAAS corrections.
There is a WAAS-compatible augmentation system called GAGAN being implemented by the Indian government. Once ready, WAAS receivers will work in India.
How accurate is the position given by GPS?
Accuracy varies depending on the type of GPS unit. In general, you can expect the position to be within 15m of its true position on earth. Techniques like Differential GPS (D-GPS) can give accuracy less than 3m. Advanced techniques like satellite augmentation, carrier-phase GPS are used for very accurate surveys and can be accurate within centimeters. You can find links to vendors of these high end systems in Buy GPS Equipment page.