عنوان مقاله [English]
Once man left his house for the first time in search of food, he needed a way to return home. The marking of rocks in the round trip, the use of coastline and celestial bodies such as the sun, the moon, and the stars were the first solutions that were less accurate and time-consuming. Later, with the development of technology of radio systems, and then the positioning satellites, routing became faster and more precise. The Global Positioning System was first created by the US Army in 1983, with an expense of $ 12 billion, and with launching the first satellite into space. This system has a variety of basic, manual and car models that have higher accuracy and cost, respectively. The system consists of three spatial, ground and user controls. The receivers will compare the time of sending the signal from the satellite with its receiving time and determine from the time difference the receiver's distance from the satellite. It is necessary to receive information from four satellites in order to find 3D coordinates. Availability in all hours of the day, any kind of weather conditions and ease of use are among the benefits of the system. Variants of this system include TRANSIT, GLONASS, SRARFIX and DORIS. System error sources include: user’s calculation errors and decrease in geometric accuracy.