An optional way to control the output shape (aspect ratio) of the bounding boxes. Defined in terms of width or height. If specified, an aspect ratio of
1.0 gives a square output; an aspect ratio of
2.0 gives twice as wide as it is high. Note that for making the output the correct aspect ratio, one of the height or width will be increased; the other dimension will not change. The pre-aspect-ratio-corrected box will be contained fully within the output box.