LLA (Latitude, Longitude, and Altitude) is the most common format for expressing geographic coordinates, representing a position on or near Earth’s surface using angular measurements (latitude and longitude) relative to the equator and prime meridian, combined with a height measurement above a reference surface. This intuitive coordinate system enables humans and navigation systems to describe any location on Earth using three values that can be easily communicated, mapped, and understood.
Latitude specifies north-south position, measured as the angle between the equatorial plane and a line perpendicular to the reference ellipsoid at the point of interest. Values range from -90° (South Pole) through 0° (equator) to +90° (North Pole). Longitude specifies east-west position, measured as the angle from the prime meridian (0°, passing through Greenwich, England) eastward or westward to the location, with values ranging from -180° to +180° (or equivalently 0° to 360°). Altitude represents the vertical distance above a reference surface, commonly the reference ellipsoid (ellipsoidal height) or mean sea level (orthometric height).
GNSS receivers natively compute positions in Earth-Centered, Earth-Fixed (ECEF) Cartesian coordinates and then convert to LLA format for user display and application output. This conversion requires knowledge of the reference ellipsoid parameters (typically WGS84 for GNSS applications) and involves iterative mathematical algorithms due to the non-linear relationship between Cartesian and geodetic coordinates. Different datums use slightly different ellipsoids, meaning the same physical location may have different LLA coordinates when expressed in different reference frames.
When working with LLA coordinates, several considerations apply. Precision requirements vary by application, one degree of latitude spans approximately 111 kilometers, while longitude degree distance varies with latitude (111 km at the equator, decreasing to zero at the poles). For meter-level positioning, coordinates must be specified to at least five or six decimal places. Additionally, the altitude component requires careful interpretation, GNSS-derived heights reference the ellipsoid, while practical applications often require heights relative to mean sea level, necessitating geoid model application for proper conversion.
