There are two -dimensional and 3 -dimensional coordinates that when GPS can receive signals of 4 or more satellites, it can calculate the local 3 -dimensional coordinates: longitude, latitude, height, if you can only receive 3 satellites with 3 satellites, Signal, it can only calculate 2 -dimensional coordinates: accuracy and latitude. At this time, height data may be displayed, but this data is invalid. Most GPS can not only display coordinates in the manner of menstruation/lat/long, but also use the coordinates such as UTM (Universal Transverse Mercator), but we generally use the LAT/Long system. This is mainly by you. The coordinate system used by the map used. The accuracy of the coordinates is opened when the Selective Availability (a measure implemented by the US Department of Defense to reduce the accuracy of GPS), the horizontal accuracy of the GPS is between 100-50 meters and deemed the satellite signal. If you have reached the GPS instructions, you can see it around, you should find your goal in about a size of a football field.

　　When SA is closed, the accuracy can reach about 15 meters. The height accuracy is worse due to the system structure. The display method of latitude and longitude can generally choose according to your hobbies. Generally, there are "hddd.dddddd", "hddd*mm.mmm" "," hddd*mm "ss.s" "" "" " ", The same below) The meridian length of the earth is 39940.67 kilometers, the latitude changes are 110.94 kilometers, 1.849 kilometers in one minute, 30.8 meters in a second, the equatorial circle is 40075.36 kilometers, the latitude of Beijing in Beijing is about 40 degrees north latitude, and the latitude circle is long. 40075*SIN (90-40), this place is 276 kilometers, a one-minute 1.42 km, 23.69 meters, you can choose a display method, and change the number of numbers to the corresponding ground. This can establish a general correspondence between latitude and actual mileage. Most GPS has the function of calculating two points, which can give the accurate distance between the two coordinates. The height display will have two ways: British and public system. Enter the Setup page of the GPS and set it into public system. This will also become public in other elephant speed and distance display.

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