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In reading around it seems clear that 4 satellites are required for a 3D fix, and while it is often stated a GPS chipset will track more than 4 satellites, literature often implies it will only use 4.

Is this true? And if so, is there a reason not to use more?

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No, this is not true. The receiver I have used, regardless of price or application, will track and utilize more than 4 satellites as part of the positioning.

  • Thanks for your answer but I'm looking for something (evidence) that tells me GPS does use it, not just reports they are available. – Paul Ridgway Oct 22 '17 at 0:18
  • Take a look at nearly any GNSS receiver, as they generally show a sky plot or a satellite count of what is utilized at the moment. There is also software available that will allow you to analyze raw data and see what signals and constellations are being utilized. – Johnson5144 Oct 23 '17 at 17:38
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"You need 3 GPS satellites for a 2D fix (i.e. no height) or 4 satellites for a 3D fix."

"GPS units often show on the screen an accuracy figure, e.g. EPE on Garmin units. Under ideal conditions, this may be 5, or even 3 metres. Manufacturers are vague on exactly how this figure is determined and it would be unwise to take this figure literally."

The more satellites the more likely of more accuracy the overhead is more processing by the chipset.

  • Thanks for your answer but I'm looking for something that tells me GPS does use it, not just reports they are available. – Paul Ridgway Oct 22 '17 at 0:17

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