Introduction to GPS

Introduction to GPS
Global Positioning System (GPS) is a navigation system designed to provide instantaneous positioning information around the world. The principle of GPS is to determine the position based on the signals from GPS satellites. Currently, there are 24 satellites orbits earth at 20,200 km altitude in 6 different orbital paths. The orbits of GPS path are inclined at 55° to equator; spaced 60° apart in longitude, so that 4 - 6 satellites are always in view.
Along with the progress of technologies, the size of GPS is getting smaller, and the cost of GPS is greatly reduced. In addition, the remove of SA (signal degradation, Selective Availability), and the recent proposed WAAS (Wide Area Augmentation System, similar to differential correction) make low cost consumer GPS to achieve an accuracy that can be used for certain research projects. In general, the GPS equips with WAAS can obtain positioning accuracy with in 3-5 m horizontal & 7 m vertical @ 95% confidence.