From ECEF to Latitude, Longitude, and Ellipsoid Height
Once the rover has solved its position in ECEF, the receiver converts that same three-dimensional point into latitude, longitude, and ellipsoid height. The position has not moved. Only the coordinate language has changed.
ECEF coordinates are excellent for computation, but they are not especially intuitive in the field. A point expressed as X, Y, and Z values measured from the center of Earth does not immediately tell us where to place a utility feature on a map or how high an antenna is above a reference surface. The receiver therefore translates the solved ECEF position into geographic coordinates that people and mapping software can use.
The Same Point in a More Familiar Form
Latitude describes the angular position north or south of the equator. Longitude describes the angular position east or west of the reference meridian. Ellipsoid height describes the point vertically relative to the mathematical ellipsoid associated with the coordinate reference system. Together, these three values describe the same position that was already solved in ECEF.
Did the coordinate actually change during this ECEF-to-latitude/longitude conversion? No. The rover did not move, and the positioning solution was not recomputed. The same point was simply expressed using a different set of coordinates.
Every coordinate system is simply a different way of describing the same point in space. Converting between coordinate systems should not change the location itself. If the numbers change dramatically, that does not necessarily mean the point moved.
Where the First Height Appears
This is the first stage in the processing chain where the result begins to look like an elevation. The receiver now has a vertical number called ellipsoid height. Because that number may be displayed in meters or feet, it is easy to assume that it represents height above mean sea level. It does not.
Ellipsoid height is the distance from the reference ellipsoid to the antenna position, measured along the ellipsoid normal. The ellipsoid is a smooth mathematical surface chosen because it is useful for positioning calculations. It does not follow coastlines, local terrain, or the gravity-defined surface that people commonly associate with sea level.
Latitude, longitude, and ellipsoid height are not a second position solution. They are a human-friendly expression of the ECEF position the rover already computed.
Ellipsoid height is a real, precise value, but it's rarely the elevation a benchmark or a project actually expects. The next chapter explains why, and introduces the piece that's still missing.