How many GNSS satellites are required for effective positioning?

Effective positioning using Global Navigation Satellite Systems (GNSS) typically requires a minimum of four satellites. This is because determining a precise position on Earth involves calculating three-dimensional coordinates (latitude, longitude, and altitude) along with accounting for the time delay of the signals sent from the satellites.

When at least four satellites are available, the GNSS receiver can utilize a process called trilateration. Each satellite provides a precise distance measurement based on the time it took for its signal to reach the receiver. Three satellites can determine a location in a 3D space, providing latitude, longitude, and altitude. However, without a fourth satellite, the system cannot resolve the ambiguities associated with potential inaccuracies in the receiver's clock. The fourth satellite helps synchronize the time within the GNSS system, allowing for accurate determination of the receiver's position.

In scenarios where only two or three satellites are in view, the receiver may not achieve accurate or reliable positioning, which is why four satellites are required for effective GNSS positioning.