function getAxisAngle(axisStart, axisEnd) {
  if (axisStart.x === axisEnd.x) {
    return axisEnd.y > axisStart.y ? Math.PI / 2 : (3 * Math.PI) / 2;
  }
  return Math.atan((axisEnd.y - axisStart.y) / (axisEnd.x - axisStart.x));
}
Compute the angle (in radians) of a decorative axis
@param {Object} axisStart Object of format {x, y} describing in coordinates
the start position of the decorative axis
@param {Object} axisEnd Object of format {x, y} describing in coordinates
the start position of the decorative axis
@returns {Number} Angle in radials