class_docstr: A structure to manage box proposals and their relations with ground truth.
docstr: Returns: #fg x4
docstr_tok: ["Returns",":","#","fg","x4"]
code: def fg_boxes(self):
      """Returns: #fg x4"""
      return tf.gather(self.boxes, self.fg_inds(), name="fg_boxes")
  
imports: import tensorflow
  from tensorpack import tfv1
  from tensorpack.models import Conv2D, FullyConnected, layer_register
  from tensorpack.tfutils.argscope import argscope
  from tensorpack.tfutils.scope_utils import under_name_scope
  from tensorpack.tfutils.summary import add_moving_summary
  from tensorpack.utils.argtools import memoized_method
  from config import config
  from utils.box_ops import pairwise_iou
  from .model_box import decode_bbox_target, encode_bbox_target
  from .backbone import GroupNorm
label_desc: Use image node_id 3 for calling the BoxProposals obj's underlying member method code with example usage: obj.fg_boxes() and returns: tf