code: def encode_delta(self, gt_box_list, fg_anchor_list):
      px, py, pw, ph = (
          fg_anchor_list[:, 0],
          fg_anchor_list[:, 1],
          fg_anchor_list[:, 2],
          fg_anchor_list[:, 3],
      )
      gx, gy, gw, gh = (
          gt_box_list[:, 0],
          gt_box_list[:, 1],
          gt_box_list[:, 2],
          gt_box_list[:, 3],
      )
      dx = (gx - px) / pw
      dy = (gy - py) / ph
      dw = np.log(gw / pw)
      dh = np.log(gh / ph)
      return np.stack([dx, dy, dw, dh], axis=1)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from numbers import Integral
  import cv2
  import copy
  import numpy
  import random
  import math
  from .operators import BaseOperator, register_op
  from .batch_operators import Gt2TTFTarget
  from ppdet.modeling.bbox_utils import bbox_iou_np_expand
  from ppdet.utils.logger import setup_logger
  from .op_helper import gaussian_radius
label_desc: Use image node_id 3 for calling the Gt2JDETargetThres obj's underlying member method code with example usage: obj.encode_delta(gt_box_list, fg_anchor_list) and returns: np