How many satellites are needed to accurately determine a position using GPS?

To accurately determine a position using GPS, a minimum of three satellites is required for triangulation. This is because the GPS receiver calculates its position based on the time it takes for signals from different satellites to reach it. Each satellite provides a unique distance measurement to the receiver based on the time delay of the signal. With signals from three satellites, the receiver can determine a 2D position (latitude and longitude), essentially triangulating its location on the Earth.

However, to achieve a precise 3D position, including altitude, a fourth satellite is necessary. This allows the system to verify and refine the calculated position, providing not just an estimate but a more accurate fix on the receiver's location in three-dimensional space. Therefore, while three satellites can determine a position, a fourth is required to enhance accuracy and to confirm the positional data.

Having five or more satellites can further improve accuracy by providing additional corrections and redundancy in the calculations, but at least three are essential for a basic position fix, and four are necessary for accuracy verification in three dimensions.