The NGS Defines Geoid as: The equipotential surface of the Earth's gravity field which best fits, in a least squares sense, global mean sea level.
There are many way in which we can model the surface of the earth. The geoid is a way to simplify the surface of the earth so that cartographers can easily represent the earth on maps and in a GIS. Earth's surface is not evenly curved, and some areas are more elevated than others. The geoid of the earth is a representation of how the earth would be shaped if all areas were at sea level. Variations in the curve of surface of the earth would appear, but those changes are much more subtle than that of the actual terrain of the continents. These variations are caused by gravitational differences in earth's gravitational field.
Understanding the shape of the geoid is crucial to the development of a coordinate system for modeling the earth. The geoid is a more simplified average of the earth’s surface, but it is difficult to create a mathematical X,Y model that can easily reference areas on the geoid. However, if a simple geometric shape, such as an ellipsoid, is applied, a mathematical coordinate system can be used to reference the ellipsoid instead.
|Tags||datum, spheroid, model|