Add box_area_center and box_iou_center functions for cxcywh format with tests

[alperenunlu]

Related #8961

This pull request introduces new utility functions for handling bounding boxes and adds corresponding tests. The main changes include the addition of box_area_center and box_iou_center functions, as well as comprehensive tests to ensure their correctness.

New utility functions:

• torchvision/ops/boxes.py: Added box_area_center function to compute the area of bounding boxes specified by their center coordinates.
• torchvision/ops/boxes.py: Added box_iou_center function to compute the intersection-over-union (IoU) for bounding boxes specified by their center coordinates.

Documentation updates:

• docs/source/ops.rst: Updated the documentation to include box_area_center and box_iou_center.

Test additions:

• test/test_ops.py: Added TestBoxAreaCenter class with tests for box_area_center function.
• test/test_ops.py: Added TestBoxIouCenter class with tests for box_iou_center function.

Module initialization:

• torchvision/ops/__init__.py: Updated the module initialization to include box_area_center and box_iou_center [1] [2].

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/8992

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[NicolasHug]

Thanks a lot for the PR and for the benchmarks @alperenunlu !

I agree with @AntoineSimoulin 's suggestion in #8961 (comment) to not expose the new _center() functions, and instead just add a new fmt (or in_fmt) parameter to the existing box_area() and box_iou() functions.

This will reduce surface area of the API, so it'll be easier to find for users, and easier for us to maintain as well!

For the rest I will let @AntoineSimoulin take a look

[AntoineSimoulin]

Hi @alperenunlu, thanks for your patience here. I went through the PR again and pushed some small changes. To simplify the code, I integrated all the logic specific to different formats directly to the box_area, box_iou, and _box_inter_union. This should not change the logic behind your PR. Could you kindly review and let me know if this fits your needs before we merge? Thanks!

[alperenunlu]

Hi @AntoineSimoulin,

Thanks for reviewing the PR.
These changes look great, and I’ve fixed a few small issues with them.

Since we now support the xywh format, I think we should also add tests for it.

Overall, I’m very satisfied with the changes.