public S1Angle angle(){
  if (isEmpty()) {
    return S1Angle.radians(-1);
  }
  return S1Angle.radians(2 * Math.asin(Math.sqrt(0.5 * height)));
}

public S1Angle angle ( ) { if ( isEmpty ( ) ) { return S1Angle . radians ( - 1 ) ; } return S1Angle . radians ( 2 * Math . asin ( Math . sqrt ( 0.5 * height ) ) ) ; }
return the cap opening angle in radians , or a negative number for empty caps .
