Which of the following is essential for GPS functionality?

Satellite triangulation is essential for GPS functionality because it allows the system to determine a precise location on Earth. GPS works by receiving signals from multiple satellites orbiting the Earth. By measuring the time it takes for these signals to travel from the satellites to a receiver, the GPS can calculate the distance from each satellite to the receiver. With information from at least four satellites, the GPS system can use trilateration, a process that involves determining the intersection point of spheres centered on each satellite, thereby pinpointing the receiver's exact location in three-dimensional space.

The effectiveness of this triangulation process is dependent on having a line of sight to the satellites, as obstacles such as buildings or mountains can interfere with the signals. Without the ability to accurately triangulate a position using satellite data, GPS functionality would be compromised.

In contrast, while other systems like analog signals, synchronous timing, and ground-based reference systems can support navigation and positioning, they are not fundamental to the primary operation of GPS technology itself.