Definition
A location fix that specifies an aircraft's place in space using three coordinates: latitude, longitude, and altitude. In GPS, a three-dimensional position requires the receiver to track signals from at least four satellites simultaneously, allowing it to compute horizontal location and height above a reference surface.
Plain English
Where the aircraft is, given as how far north or south, how far east or west, and how high up. All three are needed to pin down a point in the sky.
Context Anchor
Seen in GPS discussions when the system has calculated the aircraft’s full location, including altitude.
Derivation
Three-dimensional simply refers to the three measurements needed to locate something in space — across, along, and up. A two-dimensional position only fixes you on a flat surface; adding altitude makes it three-dimensional.
Why Pilots Care
A GPS that has only a two-dimensional fix is not giving reliable altitude information. Knowing whether the receiver is in 2D or 3D mode tells the pilot how much of the displayed position they can trust, especially for vertical navigation.
Intuition Check
Do not think of position here as only a dot on a map. In this context, three-dimensional position includes height as well as horizontal location.
Example Sentence 1
With four satellites in view, the GPS receiver locked onto a three-dimensional position and began displaying altitude alongside latitude and longitude.
Example Sentence 2
A loss of altitude data reduces the system output from a three-dimensional position to a two-dimensional position.