code: def knn_ground_truth(self):
      logger.info("knn_ground_truth: begin")
      flat_desc = self.get_index_desc("Flat")
      self.build_index_wrapper(flat_desc)
      (
          self.gt_knn_D,
          self.gt_knn_I,
          _,
          _,
          requires,
      ) = flat_desc.index.knn_search(
          dry_run=False,
          search_parameters=None,
          query_vectors=self.query_vectors,
          k=self.k,
      )
      assert requires is None
      logger.info("knn_ground_truth: end")
  
imports: import logging
  from copy import copy
  from dataclasses import dataclass
  from operator import itemgetter
  from statistics import median, mean
  from typing import Any, Dict, List, Optional
  from .utils import dict_merge
  from .index import Index, IndexFromCodec, IndexFromFactory
  from .descriptors import DatasetDescriptor, IndexDescriptor
  import faiss
  import numpy
  from scipy.optimize import curve_fit
label_desc: Use image node_id 8 for calling the Benchmark obj's underlying member method code with example usage: obj.knn_ground_truth() without return types