Ellipsoid - 52North/IlwisCore GitHub Wiki

In geodesy, a reference ellipsoid is a mathematically-defined surface that approximates the geoid, the truer figure of the Earth and this is exactly the role it has in Ilwis. There are many historical definitions for ellipsoids, each with its own fixed set of parameters. The bulk of the projections uses one of those historical ones for the calculations in the projection mathematics. It also possible to define your own ellipsoid.