How many satellites are needed for elevation?

To accurately determine elevation, a minimum of four satellites is required. This is because triangulation, the method used to ascertain a GPS device's position, relies on signals from multiple satellites.

When a GPS receiver communicates with satellites, it calculates its position based on the time it takes for the signals to arrive. With one satellite, the receiver can only establish a sphere of possible locations. With two satellites, it can obtain two intersecting points, still leaving ambiguity. Adding a third satellite allows for two intersecting circles, which narrows down the possibilities, but with four satellites, the receiver can calculate its position in three-dimensional space, which includes both latitude and longitude as well as altitude (elevation).

Thus, the requirement of four satellites is crucial for establishing an accurate elevation in addition to positional data.