code: def _generate_gravel_patch(rectangular_roi):
      x1 = rectangular_roi[0]
      y1 = rectangular_roi[1]
      x2 = rectangular_roi[2]
      y2 = rectangular_roi[3]
      gravels = []
      area = abs((x2 - x1) * (y2 - y1))
  
      for i in range((int(area // 10))):
          x = np.random.randint(x1, x2)
          y = np.random.randint(y1, y2)
          gravels.append((x, y))
  
      return gravels
  
imports: import cv2
  import random
  import math
  import numpy
  from ..coreten import Tensor, to_tensor
  from ..annotations import Tuple, Union
  from ..color import to_hls, to_rgb, to_bgr, to_hsv, to_gray, to_lab
label_desc: Use image node_id 16 for calling a global function with example usage: _generate_gravel_patch(rectangular_roi) and returns: gravels