You can create an ellipsoid from scratch or modify an existing ellipsoid and save it as a new one.
To define an ellipsoid
The code must be unique within a category and across all coordinate systems and must not contain spaces. Only the following characters are valid: A-Z (upper or lower case), 0-9, dash, and underscore.
AutoCAD Map 3D toolset displays the description in the Coordinate System Library.
If you select Create An Ellipsoid, you must complete all four values. However once you enter Equatorial Radius and one other value, the remaining values are filled in automatically. If you select Create A Sphere, you must enter a value for Equatorial Radius only.
This parameter specifies the equatorial radius in meters. The equatorial radius is also called the semi-major axis.
Inverse Flattening: Speciy the denominator of the flattening ratio. That is, if the flattening ratio is 1/x, specifies x.
Polar Radius: Specify the polar radius in meters. The polar radius is also called the semi-minor axis.
Eccentricity Squared: Specify the eccentricity as a real number.