What is the limiting factor when elevations are produced using GNSS?

When determining elevations using Global Navigation Satellite Systems (GNSS), the critical factor is a precise geoid model. The geoid represents the mean sea level and accounts for variations in the Earth's gravitational field, providing a reference surface from which elevations can be calculated. GNSS primarily provides positional data in terms of ellipsoidal heights based on the Earth's geometric shape. However, to convert these ellipsoidal heights into orthometric heights, which are commonly used in surveying and engineering applications, it is essential to accurately determine the geoid.

The use of a precise geoid model allows for the necessary translation from ellipsoidal heights derived from GNSS measurements to the actual physical elevations above sea level. Without an accurate geoid model, the computation of height differences and the representation of terrain elevations would be flawed.

While having a clear line of sight is crucial for obtaining accurate GNSS signals, it does not directly influence the accuracy of height determination once the signals are received. A precise ellipsoid model is also important for interpreting GPS data, but it does not facilitate the conversion to orthometric heights without a geoid. A precise gravimetric model relates to gravity measurements and is typically used in conjunction with geoid determination but is not the primary factor when converting GNSS