question: public double distance ( LatLng ll ) { double er = 6366.707 ; double latFrom = Math . toRadians ( getLat ( ) ) ; double latTo = Math . toRadians ( ll . getLat ( ) ) ; double lngFrom = Math . toRadians ( getLng ( ) ) ; double lngTo = Math . toRadians ( ll . getLng ( ) ) ; double d = Math . acos ( Math . sin ( latFrom ) * Math . sin ( latTo ) + Math . cos ( latFrom ) * Math . cos ( latTo ) * Math . cos ( lngTo - lngFrom ) ) * er ; return d ; }
target:  Calculate the surface distance in kilometres from the this LatLng to the given LatLng.