class_docstr: Container for a brain surface.
  
  It is used for storing vertices, faces and morphometric data
  (curvature) of a hemisphere mesh.
  
  Parameters
  ----------
  subject : string
      Name of subject
  hemi : {'lh', 'rh'}
      Which hemisphere to load
  surf : string
      Name of the surface to load (eg. inflated, orig ...).
  subjects_dir : str | None
      If not None, this directory will be used as the subjects directory
      instead of the value set using the SUBJECTS_DIR environment variable.
  offset : float | None
      If 0.0, the surface will be offset such that the medial
      wall is aligned with the origin. If None, no offset will
      be applied. If != 0.0, an additional offset will be used.
  units : str
      Can be 'm' or 'mm' (default).
  x_dir : ndarray | None
      The x direction to use for offset alignment.
  
  Attributes
  ----------
  bin_curv : numpy.ndarray
      Curvature values stored as non-negative integers.
  coords : numpy.ndarray
      nvtx x 3 array of vertex (x, y, z) coordinates.
  curv : numpy.ndarray
      Vector representation of surface morpometry (curvature) values as
      loaded from a file.
  grey_curv : numpy.ndarray
      Normalized morphometry (curvature) data, used in order to get
      a gray cortex.
  faces : numpy.ndarray
      nfaces x 3 array of defining mesh triangles.
  hemi : {'lh', 'rh'}
      Which hemisphere to load.
  nn : numpy.ndarray
      Vertex normals for a triangulated surface.
  offset : float | None
      If float, align inside edge of each hemisphere to center + offset.
      If None, do not change coordinates (default).
  subject : string
      Name of subject.
  surf : string
      Name of the surface to load (eg. inflated, orig ...).
  units : str
      Can be 'm' or 'mm' (default).
docstr: Return number of vertices.
code: def __len__(self):
      """Return number of vertices."""
      return len(self.coords)
  
file_path: mne-python/mne/viz/_brain/surface.py
imports: from os import path
  import numpy
  from ...surface import _read_patch, complete_surface_info, read_curvature, read_surface
  from ...utils import _check_fname, _check_option, _validate_type, get_subjects_dir
label_desc: Use image node_id 3 for calling the _Surface obj's underlying member method code with example usage: obj.__len__() and returns: len