function Stereographic(position, tangentPlane) {
  this.position = position;
  if (!defined(this.position)) {
    this.position = new Cartesian2();
  }

  this.tangentPlane = tangentPlane;
  if (!defined(this.tangentPlane)) {
    this.tangentPlane = Stereographic.NORTH_POLE_TANGENT_PLANE;
  }
}
Represents a point in stereographic coordinates, which can be obtained by projecting a cartesian coordinate from one pole onto a tangent plane at the other pole.
The stereographic projection faithfully represents the relative directions of all great circles passing through its center point.
To faithfully represents angles everywhere, this is a conformal projection, which means points are projected onto an arbrary sphere.
@param {Cartesian2} [position] The steroegraphic coordinates.
@param {EllipseGeometry} [tangentPlane] The tangent plane onto which the point was projected.