code: def _egi_256(head_size):
      fname = op.join(MONTAGE_PATH, "EGI_256.csd")
      montage = _read_csd(fname, head_size)
      ch_pos = montage._get_ch_pos()
  
      # For this cap, the Nasion is the frontmost electrode,
      # LPA/RPA we approximate by putting 75% of the way (toward the front)
      # between the two electrodes that are halfway down the ear holes
      nasion = ch_pos["E31"]
      lpa = 0.75 * ch_pos["E67"] + 0.25 * ch_pos["E94"]
      rpa = 0.75 * ch_pos["E219"] + 0.25 * ch_pos["E190"]
  
      fids_montage = make_dig_montage(
          coord_frame="unknown",
          nasion=nasion,
          lpa=lpa,
          rpa=rpa,
      )
  
      montage += fids_montage  # add fiducials to montage
  
      return montage
  
imports: import csv
  import os.path
  from collections import OrderedDict
  from functools import partial
  import numpy
  from .._freesurfer import get_mni_fiducials
  from ..transforms import _sph_to_cart
  from ..utils import _pl, _soft_import, warn
  from .None import __file__
  from .montage import make_dig_montage
label_desc: Use image node_id 1 for calling a global function with example usage: _egi_256(head_size) and returns: montage