docstr: Find the higher resolution image tiles that compose this parent
  image tile.
  
  Parameters
  ----------
  collection_image
      A tuple pair containing the parent
      :class:`~cartopy.io.img_nest.ImageCollection` name and
      :class:`~cartopy.io.img_nest.Img` instance.
  
  Returns
  -------
  iterator
      An iterator of tuple pairs containing the higher resolution child
      :class:`~cartopy.io.img_nest.ImageCollection` name and
      :class:`~cartopy.io.img_nest.Img` instance that compose the parent.
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code: def subtiles(self, collection_image):
      """
      Find the higher resolution image tiles that compose this parent
      image tile.
  
      Parameters
      ----------
      collection_image
          A tuple pair containing the parent
          :class:`~cartopy.io.img_nest.ImageCollection` name and
          :class:`~cartopy.io.img_nest.Img` instance.
  
      Returns
      -------
      iterator
          An iterator of tuple pairs containing the higher resolution child
          :class:`~cartopy.io.img_nest.ImageCollection` name and
          :class:`~cartopy.io.img_nest.Img` instance that compose the parent.
  
      """
      return iter(self._ancestry.get(collection_image, []))
  
imports: import collections
  from pathlib import Path
  import numpy
  from PIL import Image
  import shapely.geometry
label_desc: Use image node_id 5 for calling the NestedImageCollection obj's underlying member method code with example usage: obj.subtiles(collection_image) and returns: iter