code: def plot_sg(img, preds, obj_classes, rel_classes, topk=1):
      """visualization of generated scene graph"""
      size = img.shape[0:2]
      box_scale = np.array([size[1], size[0], size[1], size[0]])
      topk = min(topk, preds.shape[0])
      ax = gcv.utils.viz.plot_image(img)
      for i in range(topk):
          rel = int(preds[i, 2])
          src = int(preds[i, 3])
          dst = int(preds[i, 4])
          src_name = obj_classes[src]
          dst_name = obj_classes[dst]
          rel_name = rel_classes[rel]
          src_bbox = preds[i, 5:9] * box_scale
          dst_bbox = preds[i, 9:13] * box_scale
  
          src_center = np.array(
              [
                  (src_bbox[0] + src_bbox[2]) / 2,
                  (src_bbox[1] + src_bbox[3]) / 2,
              ]
          )
          dst_center = np.array(
              [
                  (dst_bbox[0] + dst_bbox[2]) / 2,
                  (dst_bbox[1] + dst_bbox[3]) / 2,
              ]
          )
          rel_center = (src_center + dst_center) / 2
  
          line_x = np.array(
              [
                  (src_bbox[0] + src_bbox[2]) / 2,
                  (dst_bbox[0] + dst_bbox[2]) / 2,
              ]
          )
          line_y = np.array(
              [
                  (src_bbox[1] + src_bbox[3]) / 2,
                  (dst_bbox[1] + dst_bbox[3]) / 2,
              ]
          )
  
          ax.plot(
              line_x,
              line_y,
              linewidth=3.0,
              alpha=0.7,
              color=plt.cm.cool(rel),
          )
  
          ax.text(
              src_center[0],
              src_center[1],
              "{:s}".format(src_name),
              bbox=dict(alpha=0.5),
              fontsize=12,
              color="white",
          )
          ax.text(
              dst_center[0],
              dst_center[1],
              "{:s}".format(dst_name),
              bbox=dict(alpha=0.5),
              fontsize=12,
              color="white",
          )
          ax.text(
              rel_center[0],
              rel_center[1],
              "{:s}".format(rel_name),
              bbox=dict(alpha=0.5),
              fontsize=12,
              color="white",
          )
      return ax
  
label_desc: Use image node_id 1 for calling a global function with example usage: plot_sg(img, preds, obj_classes, rel_classes, topk) and returns: ax