class_docstr: Calculate the area of bounding boxes.
  
  Parameters
  ----------
  fmt : str, default is corner
      Bounding box format, can be {'center', 'corner'}.
      'center': {x, y, width, height}
      'corner': {xmin, ymin, xmax, ymax}
  axis : int, default is -1
      Effective axis of the bounding box. Default is -1(the last dimension).
  
  Returns
  -------
  A BxNx1 NDArray
class_docstr_tok: ["Calculate","the","area","of","bounding","boxes",".","Parameters","--","--","--","--","--","fmt",":","str",",","default","is","corner","Bounding","box","format",",","can","be","{","'center","'",",","'corner","'","}",".","'center","'",":","{","x",",","y",",","width",",","height","}","'corner","'",":","{","xmin",",","ymin",",","xmax",",","ymax","}","axis",":","int",",","default","is","-1","Effective","axis","of","the","bounding","box",".","Default","is","-1","(","the","last","dimension",")",".","Returns","--","--","--","-","A","BxNx1","NDArray"]
code: def __init__(self, axis=-1, fmt="corner", **kwargs):
      super(BBoxArea, self).__init__(**kwargs)
      if fmt.lower() == "corner":
          self._pre = BBoxCornerToCenter(split=True)
      elif fmt.lower() == "center":
          self._pre = BBoxSplit(axis=axis)
      else:
          raise ValueError(
              "Unsupported format: {}. Use 'corner' or 'center'.".format(
                  fmt
              )
          )
  
imports: from __future__ import absolute_import
  import numpy
  from mxnet import gluon
label_desc: Use image node_id 1 to create a new BBoxArea object from inherited base classes: gluon with example: obj = BBoxArea(axis, fmt)