What is the term for the process of using 4 satellites or cell phone towers to locate a smartphone (or tracking device), including its altitude?

Question

What is the process of using 4 satellites or cell phone towers to locate a smartphone (or tracking device), including its altitude, called? I know for 2D this is trilateration but can't find a word for the 3D equivalent.

Answer 1

The process you are referring to is still called trilateration. In fact, the term "trilateration" can be used for both 2D and 3D positioning.

To clarify:

• Trilateration is the process of determining the location of a point (in 2D or 3D) by measuring distances to it from known points at the end of fixed baselines, rather than measuring angles to it as with triangulation.

For 2D positioning, you'd indeed need at least three non-collinear points (e.g., three cell towers) to uniquely determine a location. Each tower provides a radius and, conceptually, these radii intersect at points, with the true position being where the circles overlap.

For 3D positioning, such as with the Global Positioning System (GPS), you need measurements from at least four satellites. This is because each satellite provides a sphere of possible locations. The intersection of these spheres will give a unique point in three-dimensional space (or more precisely, it will typically give two possible points, one of which can usually be discarded as not being on the Earth's surface). The fourth satellite is also crucial to correct for time discrepancies between the satellite clocks and the receiver's clock.

Do note: In practice, with real-world imperfections and the desire for increased accuracy, more than the minimum number of measurements might be used.

In conclusion, the term you're looking for, whether in 2D or 3D, is still trilateration.