^^Geoide. Geodesia.

http://en.wikipedia.org/wiki/Earth's_gravity
  1. Valore della gravita' terrestre g.
  2. Modello geometrico della Terra.

 

 

 

The geoid is a model of global mean sea level that is used to measure precise surface elevations. >>>


 

Links

The NGS Geoid page http://www.ngs.noaa.gov/GEOID/

http://oceanservice.noaa.gov/facts/geoid.html

 

https://en.wikipedia.org/wiki/Geodesy