code: def forward(self, images, features, gt_instances=None):
      assert not self.training
      features = [features[f] for f in self.in_features]
      objectness_logits_pred, anchor_deltas_pred = self.rpn_head(
          features
      )
      return self._generate_proposals(
          images,
          objectness_logits_pred,
          anchor_deltas_pred,
          gt_instances,
      )
  
imports: import math
  from typing import Dict
  import torch
  import torch.nn.functional
  from detectron2.layers import ShapeSpec, cat
  from detectron2.layers.roi_align_rotated import ROIAlignRotated
  from detectron2.modeling import poolers
  from detectron2.modeling.proposal_generator import rpn
  from detectron2.modeling.roi_heads.mask_head import mask_rcnn_inference
  from detectron2.structures import Boxes, ImageList, Instances, Keypoints, RotatedBoxes
  from .shared import alias, to_device
label_desc: Use image node_id 3 for calling the Caffe2RPN obj's underlying member method code with example usage: obj.forward(images, features, gt_instances) and returns: self