I was checking my NMEA data and noticed that the number of satellites in view is always higher than the number of satellites actually being used for positioning. What is the difference between "visible" and "used" satellites?
Hello! That is a very common observation. To put it simply:
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Visible Satellites (Satellites in View): These are all the satellites that are physically above the horizon and being actively tracked by your receiver’s RF antenna. You can see this total number in the GPGSV message.
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Used Satellites: These are the "elite" satellites. After the receiver tracks all visible satellites, it runs them through a strict quality control process. Only the satellites with high-quality signals are actually used in the mathematical calculation to determine your final position. You can see the number of used satellites in the GPGGA message.
