GPS Basics

　　1. Satellite trajectory: There are 24 GPS satellites orbiting the earth along six orbits (in groups of four). Generally, there are no more than 12 satellites on the same side of the earth. Most GPS receivers can track 8 to 12 satellites. satellite. At least 3 satellites are required to calculate LAT/LONG (2D) coordinates. Add one more to calculate 3-dimensional coordinates. For a given location, the GPS receiver knows which satellites are nearby at the time because it is constantly receiving updates from the satellites.

　　2. Parallel channels: Some consumer GPS devices have 2 to 5 parallel channels to receive satellite signals. Because up to 12 satellites may be visible (the average is 8), this means that the GPS receiver must visit each satellite in sequence to obtain information about each satellite. Most GPS receivers on the market are of the 20-parallel channel type, which allows them to continuously track the information of each satellite. The advantages of 12-channel receivers include fast cold start and initialization of satellite information, and can have more information in forest areas. good reception. Generally 20-channel receiver does not needTo external antenna, unless you are in an enclosed space, such as cabin, car.

　　3. Positioning time: This is the time it takes to determine your current location when you restart your GPS receiver. For a 20-channel receiver, if you are near the location of the last fix, the fix time is generally 3 to 5 minutes for a cold start and 15 to 30 seconds for a hot start.

　　4. Positioning accuracy: The horizontal position positioning accuracy of most GPS receivers is about 2.93m to 29.3m.

　　5. Signal interference: To give you a good positioning, the GPS receiver needs at least 3 to 5 satellites to be visible. If you're in a canyon or on a street lined with tall buildings, or in a dense jungle, you may not be able to communicate with enough satellites to be able to locate or get only two-dimensional coordinates. Also, if you are inside a building, you may not be able to update your location, some GPS receivers have separate antennas that can be attached to the windshield, or an external antenna that can be placed on the roof of the car, which helps you receivers get more satellite signals.

　　6. Physical indicators: When purchasing GPS equipment, physical indicators such as size, weight, display screen, waterproof, shockproof, dustproof performance, high temperature resistance, and power consumption must be considered.

　　7. What is the baud rate of general GPS?

　　4800. Now there are more and more GPS signs that can provide higher speed, but it is not necessary for GPS applications, and some will cause system instability.

　　8. Why is my GPS always floating around, even when standing still?

　　Due to the relatively weak ability to collect satellites, the earlier GPS always had a disconnection, especially when it was used for navigation in the city, which caused a lot of inconvenience to travel. Some civilian GPS chips developed later included GPS signals with insufficient signals, which caused the phenomenon of drift. But in the same situation, the older GPS products will be completely disconnected, and will not start accepting until a satellite with a strong enough signal can be found. So this is a relatively contradictory choice, but with the continuous development and upgrading of software and hardware, I believe this situation will become less and less.

　　9. I was able to locate yesterday, but I can't locate it today, why?

　　Generally, the GPS was not properly turned off when it was last used. Please restart the device and connect it again. If it still doesn't work, cold start the GPS. In future use, be sure to disable GPS in the software before turning off or unplugging the GPS receiver.

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Introduction to GPS Navigation System