S1Angle.this - multiple declarations

Function S1Angle.this

Return the angle between two points, which is also equal to the distance between these points on the unit sphere. The points do not need to be normalized. This function has a maximum error of 3.25 * DBL_EPSILON (or 2.5 * double.epsilon for angles up to 1 radian).

this (
  in const(s2.util.math.vector.Vector!(double,3L)) x,
  in const(s2.util.math.vector.Vector!(double,3L)) y
);

Function S1Angle.this

Like the constructor above, but return the angle (i.e., distance) between two S2LatLng points. This function has about 15 digits of accuracy for small distances but only about 8 digits of accuracy as the distance approaches 180 degrees (i.e., nearly-antipodal points).

this (
  in const(s2.s2latlng.S2LatLng) x,
  in const(s2.s2latlng.S2LatLng) y
);