function pointDistance(x1, y1, x2, y2) {
  const xx = Math.pow(x2 - x1, 2);
  const yy = Math.pow(y2 - y1, 2);
  return (Math.sqrt(xx + yy));
}
@param {Number} x1
@param {Number} y1
@param {Number} x2
@param {Number} y2
@return {Number}