1. Satellite trajectory

　　Here are 24 GPS satellites running around the earth along six orbits (a group of four). Generally, there are no more than 12 satellites on the same side of the earth. Most GPS receivers can track 8-12 satellites. Calculating LAT/Long (2D) coordinates requires at least 3 satellites. You can calculate 3 -dimensional coordinates. For a given position, the GPS receiver knows which satellites are near at this time because it constantly receives a update signal from the satellite.

　　2. Paying channel

　　Some consumer GPS devices have 2 to 5 parallel channels to receive satellite signals. Because at most 12 satellites are visible (the average is 8), which means that the GPS receiver must access each satellite in order to obtain the information of each satellite.

　　Most of the GPS receivers on the market are 12 parallel channel types, which allows them to continuously track the information of each satellite. The advantages of the 12 -channel receiver include the information of the fast -cold start and initialization satellite. Good receiving effect. Generally, the 12 -channel receiver does not require an external antenna, unless you are in a closed space, such as the cabin and compartment.

　　3. Positioning time

　　This means that when you restart your GPS receiver, it determines the time required for the current location. For the 12 -channel receiver, if you are near the last positioning position, the positioning time when the cold start is generally 3-5 minutes, and the hot start is 15-30 seconds. For the 2 channel receiver, most of the time when the cold starts exceeds more than the cold startup exceeding the starting start, most of the when the cold starts exceeds more than the cold startup exceeding the starter. 15 minutes, 2 to 5 minutes at the time of hot start.

　　4. Positioning accuracy

　　The level positioning accuracy of most GPS receivers is about 5m to 10m, but this is only when SA is not turned on.

　　5. DGPS function

　　In order to minimize the impact of the refraction of the SA and the atmosphere, there is a device called the DGPS sender. It is a fixed GPS receiver (set in a radius of 100km to 200km at a exploration site) to receive the satellite signal. Compared, then calculated the "difference", which is very close to the impact of the refraction of SA and the atmosphere. It sends this difference, and other GPS receivers can use it to obtain a more accurate position reading (5m to 10m or less or less Error).

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