Find intersection over union-area for given two boxes.
            It the ratio of intersection-area / union-area

        :param box1: Box object 1
        :param box2: Box object 2
        :return: Intersection-over-union value

def iou(box1, box2):
        """
        Find intersection over union-area for given two boxes.
            It the ratio of intersection-area / union-area

        :param box1: Box object 1
        :param box2: Box object 2
        :return: Intersection-over-union value
        """
        int_box = Box.intersection_box(box1, box2)
        int_area = int_box.area()
        union_area = box1.area() + box2.area() - int_area

        result = 0.0
        if union_area > 0:
            result = float(int_area) / float(union_area)

        return result