class_docstr: Making binary mask from detection data with ICDAR format.
  Typically following the process of class `MakeICDARData`.
docstr: compute polygon area
docstr_tok: ["compute","polygon","area"]
code: def polygon_area(self, polygon):
      """
      compute polygon area
      """
      area = 0
      q = polygon[-1]
      for p in polygon:
          area += p[0] * q[1] - p[1] * q[0]
          q = p
      return area / 2.0
  
file_path: PaddleOCR/ppocr/data/imaug/make_shrink_map.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  import numpy
  import cv2
  from shapely.geometry import Polygon
  import pyclipper
label_desc: Use image node_id 4 for calling the MakeShrinkMap obj's underlying member method code with example usage: obj.polygon_area(polygon) and returns: unknown