Geodetic Journey

The ability to use GNSS satellites for height determination has been a long lasting objective for geodesists. This requires access to a high precision geoid model. Within the last decade significant improvements in the methodology of geoid determination has been made. Detailed digital terrain models and better global geopotentialmodels have become available, and significant improvements in the gravity coverage has been made. Airborne gravity surveys is now a very cost efficient way of mapping the gravity field supplying geodesists with high quality data to be used in determining the geoid.

Traditionally heights on land were determined by spirit levelling. A very time consuming and expensive method. Most heights and national height systems are determined in this way.

The last decade has witnessed the derivation of geoid models adjusted to the local vertical height datum by using GNSS measurements at levelling bench marks. Such a model allows heights to be determined in the local vetical datum with a precision of 1-2 cm when using GNSS satellites for areas with access to a high precision geoid model.

Some countries have abandoned or bypassed a national levelling based height system and have decided to use one based on the geoid. As the knowledge of geoid and its precision improves, more countries will be choosing this alternative in the future.