question: public static double pointCircleDistance ( Geo p1 , Geo p2 , Geo center ) { Geo n = Geo . crossNormalize ( p1 , p2 , new Geo ( ) ) ; Geo c = center . normalize ( new Geo ( ) ) ; double cosTheta = Geo . dot ( n , c ) ; double theta = Math . acos ( cosTheta ) ; return Math . abs ( Math . PI / 2 - theta ) ; }
target:  Calculates the great circle distance from the point (center) to the great circle containing the points (p1) and (p2).