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 hybrid_forward(self, F, x):
      _, _, width, height = self._pre(x)
      width = F.where(width > 0, width, F.zeros_like(width))
      height = F.where(height > 0, height, F.zeros_like(height))
      return width * height
  
imports: from __future__ import absolute_import
  import numpy
  from mxnet import gluon
label_desc: Use image node_id 2 for calling the BBoxArea obj's underlying member method code with example usage: obj.hybrid_forward(F, x) and returns: unknown