class_docstr: Creates ShapelyAnnotation (as shapely MultiPolygon).
  Can convert this instance annotation to various formats.
docstr: [xmin, ymin, width, height]
docstr_tok: ["[","xmin",",","ymin",",","width",",","height","]"]
code: def to_xywh(self):
      """
      [xmin, ymin, width, height]
      """
      if self.multipolygon.area != 0:
          coco_bbox, _ = get_bbox_from_shapely(self.multipolygon)
          # fix coord by slice box
          if self.slice_bbox:
              minx = self.slice_bbox[0]
              miny = self.slice_bbox[1]
              coco_bbox[0] = coco_bbox[0] - minx
              coco_bbox[1] = coco_bbox[1] - miny
      else:
          coco_bbox: List = []
      return coco_bbox
  
imports: from typing import List
  from shapely.geometry import CAP_STYLE, JOIN_STYLE, MultiPolygon, Polygon, box
label_desc: Use image node_id 10 for calling the ShapelyAnnotation obj's underlying member method code with example usage: obj.to_xywh() and returns: coco_bbox