class_docstr: Creates ShapelyAnnotation (as shapely MultiPolygon).
  Can convert this instance annotation to various formats.
docstr: [
      [[[1, 1]], [[325, 125]], [[250, 200]], [[5, 200]]],
      [[[1, 1]], [[325, 125]], [[250, 200]], [[5, 200]]]
  ]
docstr_tok: ["[","[","[","[","1",",","1","]","]",",","[","[","325",",","125","]","]",",","[","[","250",",","200","]","]",",","[","[","5",",","200","]","]","]",",","[","[","[","1",",","1","]","]",",","[","[","325",",","125","]","]",",","[","[","250",",","200","]","]",",","[","[","5",",","200","]","]","]","]"]
code: def to_opencv_contours(self):
      """
      [
          [[[1, 1]], [[325, 125]], [[250, 200]], [[5, 200]]],
          [[[1, 1]], [[325, 125]], [[250, 200]], [[5, 200]]]
      ]
      """
      opencv_contours: List = []
      for shapely_polygon in self.multipolygon.geoms:
          # create opencv_contour for selected shapely_polygon
          if shapely_polygon.area != 0:
              x_coords = shapely_polygon.exterior.coords.xy[0]
              y_coords = shapely_polygon.exterior.coords.xy[1]
              # fix coord by slice_bbox
              if self.slice_bbox:
                  minx = self.slice_bbox[0]
                  miny = self.slice_bbox[1]
                  x_coords = [x_coord - minx for x_coord in x_coords]
                  y_coords = [y_coord - miny for y_coord in y_coords]
              opencv_contour = [
                  [[int(x_coords[ind]), int(y_coords[ind])]]
                  for ind in range(len(x_coords))
              ]
          else:
              opencv_contour: List = []
          # append opencv_contour to opencv_contours
          opencv_contours.append(opencv_contour)
      # return result
      return opencv_contours
  
imports: from typing import List
  from shapely.geometry import CAP_STYLE, JOIN_STYLE, MultiPolygon, Polygon, box
label_desc: Use image node_id 9 for calling the ShapelyAnnotation obj's underlying member method code with example usage: obj.to_opencv_contours() and returns: opencv_contours