getAngle(referenceVector = null, returnAsDegrees = false) {
    let u = null;

    if (!referenceVector) {
      u = Vector2.subtract(this.position, this.previousPosition);
    } else {
      u = Vector2.subtract(this.position, referenceVector);
    }

    if (returnAsDegrees) {
      return MathHelper.toDeg(u.angle());
    }

    return u.angle();
  }
Returns the angle of this vertexes positional vector. If a reference vector is supplied in relations to this vector, else in relations to the coordinate system.

@param {Vector2} [referenceVector=null] - The reference vector.
@param {Boolean} [returnAsDegrees=false] - If true, returns angle in degrees, else in radians.
@returns {Number} The angle of this vertex.