GPS satellite positioning system
GPS Global PosiTIoning System
GPS is the global satellite radio positioning system. It uses 4 sets of 6 orbits, each of which has a total of 24 at an altitude of about 20180Km. The stellar synchronous satellite emits a radio signal of 1575.42MHz. The time difference of the signal is detected and the global positioning can be accurately reached about 30 to 100 meters. Longitude and latitude display of accuracy.
The earth is a non-circular sphere with an equatorial radius of 6378.14Km, a polar radius of 6536.755Km, an equatorial circle of about 40075.04Km, and a speed of light of 29979.458Km / S (defined value). The equatorial circle is divided into 360 °, that is, 40075.04Km ÷ 360 ° = 111.31955Km / "÷ 60 '= 1.8553258Km / 1" ÷ 60 "= 30.92 meters / second.
1 浬 = 1852 meters, which is a distance of about 1 minute. The latitude and longitude is 360 °, 1 ″ = 60 ′ (minutes), 1 ′ = 60 ″ (seconds).
1 mile = 1760 yards × 3 = 5280 feet = 1609.35 meters.
1 ham = 6076.1 feet = 1.516 miles = 1852.00 meters.
GPS position indication can be set to latitude and longitude degrees, minutes and seconds, about 30 meters per second, so the accuracy is about 30 meters, the difference between east and west longitude is about 1.682 kilometers, and the difference between north and south latitude is about 111.2 Km / 60 = 1.8533Km ÷ 60 = 30.888 meters. Note that it is a 60-bit carry. If it is a 10/100 carry, it must be converted carefully to avoid mistakes.
The GPS satellite is at an altitude of 20,000 to 25,000 kilometers, and the path loss of the 1.8GHz signal is about 180 to 185db. If it reaches the receiving antenna with 700W power without blocking, there will be about 0.1 to 1uV signal. The satellites are synchronized by stars, and there are 4 minutes of detailed orbit information and signal strength every day. Please refer to the IT program of the GPS orbit data for details. (The version of BV2AP input satellite data) Note: the frequency increases by 3 times, the path loss difference is 10db, that is 101 times / 10 times, the signal strength of the top of the ground plane is almost within a few db, that is, 10 times, mostly between 3 and 10db , The path loss is mostly in 130 ~ 180db.
The operation of GPS must first set the original parameters of the internal start-up, including the unit of metric kilometers, meters, latitude and longitude degrees 60 seconds, the time difference between local time and UTC, and the most important projection standards for map mapping. Different DATUMs need to be selected. If it is GPS, it can be set to the WGS84 standard, otherwise it is normal for the distance to the map on hand to be several kilometers.
Because the GPS reading is the average value of RMS, it is best to check and record the readings several times in a row. The more accurate the measurement, the more accurate the satellites are, and the better the 5 satellites receive at the same time. The normal error is about 30 meters. However, after the Iran-Iraq War, the US Department of Defense has reduced the accuracy to about 100 meters. (Multiple measurements can be averaged within 30 meters)
The original use of GPS can be found in the open space for dozens of minutes, and automatically receive the memory satellite track data, so that the synchronized reading of each use of 30 seconds to 90 seconds can be accelerated (that is, POWER ON is turned on to display the latitude and longitude for 30 seconds, and Displayed every 1 to 3 seconds).
Good GPS hopes to save power, small size, light weight, and can receive more signals simultaneously. It is best to use the urban area to display the number of satellites, location, and signal strength. It is of course better to display the map screen with ROM or PC. External Standard intercom with serial signal output interface.
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