question: private static Double computeAngle ( final GeoPoint point , final double sinLatitude , final double cosLatitude , final double sinLongitude , final double cosLongitude ) { final double x1 = point . x * cosLongitude + point . y * sinLongitude ; final double y1 = - point . x * sinLongitude + point . y * cosLongitude ; final double z1 = point . z ; final double y2 = y1 ; final double z2 = - x1 * sinLatitude + z1 * cosLatitude ; if ( Math . sqrt ( y2 * y2 + z2 * z2 ) < Vector . MINIMUM_RESOLUTION ) { return null ; } return Math . atan2 ( z2 , y2 ) ; }
target:  Compute the angle for a point given rotation information.