code: def lookat_camera(vertices, eye, at=None, up=None):
      """'look at' transformation: from world space to camera space
      standard camera space:
          camera located at the origin.
          looking down negative z-axis.
          vertical vector is y-axis.
      Xcam = R(X - C)
      Homo: [[R, -RC], [0, 1]]
      Args:
        vertices: [nver, 3]
        eye: [3,] the XYZ world space position of the camera.
        at: [3,] a position along the center of the camera's gaze.
        up: [3,] up direction
      Returns:
        transformed_vertices: [nver, 3]
      """
      if at is None:
          at = np.array([0, 0, 0], np.float32)
      if up is None:
          up = np.array([0, 1, 0], np.float32)
  
      eye = np.array(eye).astype(np.float32)
      at = np.array(at).astype(np.float32)
      z_aixs = -normalize(at - eye)  # look forward
      x_aixs = normalize(np.cross(up, z_aixs))  # look right
      y_axis = np.cross(z_aixs, x_aixs)  # look up
  
      R = np.stack((x_aixs, y_axis, z_aixs))  # , axis = 0) # 3 x 3
      transformed_vertices = vertices - eye  # translation
      transformed_vertices = transformed_vertices.dot(R.T)  # rotation
      return transformed_vertices
  
file_path: insightface/python-package/insightface/thirdparty/face3d/mesh/transform.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import numpy
  import math
  from math import cos, sin
label_desc: Use image node_id 6 for calling a global function with example usage: lookat_camera(vertices, eye, at, up) and returns: transformed_vertices