docstr: Calculate the angle between vector AB and x-axis positive direction.
docstr_tok: ["Calculate","the","angle","between","vector","AB","and","x-axis","positive","direction","."]
code: def vector_angle(self, A, B):
      """
      Calculate the angle between vector AB and x-axis positive direction.
      """
      AB = np.array([B[1] - A[1], B[0] - A[0]])
      return np.arctan2(*AB)
  
imports: import math
  import cv2
  import numpy
  import json
  import sys
  import os
label_desc: Use image node_id 14 for calling the SASTProcessTrain obj's underlying member method code with example usage: obj.vector_angle(A, B) and returns: np