code: def bbox_random_crop_with_constraints(
      bbox,
      size,
      min_scale=0.3,
      max_scale=1,
      max_aspect_ratio=2,
      constraints=None,
      max_trial=50,
  ):
      """Crop an image randomly with bounding box constraints.
  
      This data augmentation is used in training of
      Single Shot Multibox Detector [#]_. More details can be found in
      data augmentation section of the original paper.
      .. [#] Wei Liu, Dragomir Anguelov, Dumitru Erhan, Christian Szegedy,
         Scott Reed, Cheng-Yang Fu, Alexander C. Berg.
         SSD: Single Shot MultiBox Detector. ECCV 2016.
  
      Parameters
      ----------
      bbox : numpy.ndarray
          Numpy.ndarray with shape (N, 4+) where N is the number of bounding boxes.
          The second axis represents attributes of the bounding box.
          Specifically, these are :math:`(x_{min}, y_{min}, x_{max}, y_{max})`,
          we allow additional attributes other than coordinates, which stay intact
          during bounding box transformations.
      size : tuple
          Tuple of length 2 of image shape as (width, height).
      min_scale : float
          The minimum ratio between a cropped region and the original image.
          The default value is :obj:`0.3`.
      max_scale : float
          The maximum ratio between a cropped region and the original image.
          The default value is :obj:`1`.
      max_aspect_ratio : float
          The maximum aspect ratio of cropped region.
          The default value is :obj:`2`.
      constraints : iterable of tuples
          An iterable of constraints.
          Each constraint should be :obj:`(min_iou, max_iou)` format.
          If means no constraint if set :obj:`min_iou` or :obj:`max_iou` to :obj:`None`.
          If this argument defaults to :obj:`None`, :obj:`((0.1, None), (0.3, None),
          (0.5, None), (0.7, None), (0.9, None), (None, 1))` will be used.
      max_trial : int
          Maximum number of trials for each constraint before exit no matter what.
  
      Returns
      -------
      numpy.ndarray
          Cropped bounding boxes with shape :obj:`(M, 4+)` where M <= N.
      tuple
          Tuple of length 4 as (x_offset, y_offset, new_width, new_height).
  
      """
      # default params in paper
      if constraints is None:
          constraints = (
              (0.1, None),
              (0.3, None),
              (0.5, None),
              (0.7, None),
              (0.9, None),
              (None, 1),
          )
  
      w, h = size
  
      candidates = [(0, 0, w, h)]
      for min_iou, max_iou in constraints:
          min_iou = -np.inf if min_iou is None else min_iou
          max_iou = np.inf if max_iou is None else max_iou
  
          for _ in range(max_trial):
              scale = random.uniform(min_scale, max_scale)
              aspect_ratio = random.uniform(
                  max(1 / max_aspect_ratio, scale * scale),
                  min(max_aspect_ratio, 1 / (scale * scale)),
              )
              crop_h = int(h * scale / np.sqrt(aspect_ratio))
              crop_w = int(w * scale * np.sqrt(aspect_ratio))
  
              crop_t = random.randrange(h - crop_h)
              crop_l = random.randrange(w - crop_w)
              crop_bb = np.array(
                  (crop_l, crop_t, crop_l + crop_w, crop_t + crop_h)
              )
  
              if len(bbox) == 0:
                  top, bottom = crop_t, crop_t + crop_h
                  left, right = crop_l, crop_l + crop_w
                  return bbox, (left, top, right - left, bottom - top)
  
              iou = bbox_iou(bbox, crop_bb[np.newaxis])
              if min_iou <= iou.min() and iou.max() <= max_iou:
                  top, bottom = crop_t, crop_t + crop_h
                  left, right = crop_l, crop_l + crop_w
                  candidates.append(
                      (left, top, right - left, bottom - top)
                  )
                  break
  
      # random select one
      while candidates:
          crop = candidates.pop(np.random.randint(0, len(candidates)))
          new_bbox = bbox_crop(bbox, crop, allow_outside_center=False)
          if new_bbox.size < 1:
              continue
          new_crop = (crop[0], crop[1], crop[2], crop[3])
          return new_bbox, new_crop
      return bbox, (0, 0, w, h)
  
file_path: mxnet/python/mxnet/gluon/contrib/data/vision/transforms/bbox/utils.py
imports: from __future__ import division
  import random
  import numpy
label_desc: Use image node_id 10 for calling a global function with example usage: bbox_random_crop_with_constraints(bbox, size, min_scale, max_scale, max_aspect_ratio, constraints, max_trial) and returns: bbox,  int,  int,  w,  h, new_bbox,  new_crop, bbox,  left,  top,  unknown,  unknown