code: def _forward_train(self):
      feats = self.backbone.forward_features(self.inputs["image"])
      vitpost_output = self.head(feats)
      return self.loss(vitpost_output, self.inputs)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import paddle
  import numpy
  import math
  import cv2
  from ppdet.core.workspace import register, create, serializable
  from .meta_arch import BaseArch
  from ..keypoint_utils import transform_preds
  from ..None import layers
label_desc: Use image node_id 3 for calling the VitPose_TopDown obj's underlying member method code with example usage: obj._forward_train() and returns: self