content: from yacs.config import CfgNode as CN
  
  
  def lower_config(yacs_cfg):
      if not isinstance(yacs_cfg, CN):
          return yacs_cfg
      return {k.lower(): lower_config(v) for k, v in yacs_cfg.items()}
  
  
  _CN = CN()
  _CN.BACKBONE_TYPE = 'ResNetFPN'
  _CN.RESOLUTION = (8, 2)  # options: [(8, 2), (16, 4)]
  _CN.FINE_WINDOW_SIZE = 5  # window_size in fine_level, must be odd
  _CN.FINE_CONCAT_COARSE_FEAT = True
  
  # 1. LoFTR-backbone (local feature CNN) config
  _CN.RESNETFPN = CN()
  _CN.RESNETFPN.INITIAL_DIM = 128
  _CN.RESNETFPN.BLOCK_DIMS = [128, 196, 256]  # s1, s2, s3
  
  # 2. LoFTR-coarse module config
  _CN.COARSE = CN()
  _CN.COARSE.D_MODEL = 256
  _CN.COARSE.D_FFN = 256
  _CN.COARSE.NHEAD = 8
  _CN.COARSE.LAYER_NAMES = ['self', 'cross'] * 4
  _CN.COARSE.ATTENTION = 'linear'  # options: ['linear', 'full']
  _CN.COARSE.TEMP_BUG_FIX = False
  
  # 3. Coarse-Matching config
  _CN.MATCH_COARSE = CN()
  _CN.MATCH_COARSE.THR = 0.2
  _CN.MATCH_COARSE.BORDER_RM = 2
  _CN.MATCH_COARSE.MATCH_TYPE = 'dual_softmax'  # options: ['dual_softmax, 'sinkhorn']
  _CN.MATCH_COARSE.DSMAX_TEMPERATURE = 0.1
  _CN.MATCH_COARSE.SKH_ITERS = 3
  _CN.MATCH_COARSE.SKH_INIT_BIN_SCORE = 1.0
  _CN.MATCH_COARSE.SKH_PREFILTER = True
  _CN.MATCH_COARSE.TRAIN_COARSE_PERCENT = 0.4  # training tricks: save GPU memory
  _CN.MATCH_COARSE.TRAIN_PAD_NUM_GT_MIN = 200  # training tricks: avoid DDP deadlock
  
  # 4. LoFTR-fine module config
  _CN.FINE = CN()
  _CN.FINE.D_MODEL = 128
  _CN.FINE.D_FFN = 128
  _CN.FINE.NHEAD = 8
  _CN.FINE.LAYER_NAMES = ['self', 'cross'] * 1
  _CN.FINE.ATTENTION = 'linear'
  
  default_cfg = lower_config(_CN)
  