undergroundColorAlphaByDistance
Gets or sets the near and far distance for blending Globe.undergroundColor with the globe color. The alpha will interpolate between the NearFarScalar.nearValue and NearFarScalar.farValue while the camera distance falls within the lower and upper bounds of the specified NearFarScalar.near and NearFarScalar.far. Outside of these ranges the alpha remains clamped to the nearest bound. If undefined, the underground color will not be blended with the globe color.
When the camera is above the ellipsoid the distance is computed from the nearest point on the ellipsoid instead of the camera's position.