class_docstr: Tracker for OC-SORT.
  
  Args:
      motion (dict): Configuration of motion. Defaults to None.
      obj_score_thrs (float): Detection score threshold for matching objects.
          Defaults to 0.3.
      init_track_thr (float): Detection score threshold for initializing a
          new tracklet. Defaults to 0.7.
      weight_iou_with_det_scores (bool): Whether using detection scores to
          weight IOU which is used for matching. Defaults to True.
      match_iou_thr (float): IOU distance threshold for matching between two
          frames. Defaults to 0.3.
      num_tentatives (int, optional): Number of continuous frames to confirm
          a track. Defaults to 3.
      vel_consist_weight (float): Weight of the velocity consistency term in
          association (OCM term in the paper).
      vel_delta_t (int): The difference of time step for calculating of the
          velocity direction of tracklets.
      init_cfg (dict or list[dict], optional): Initialization config dict.
          Defaults to None.
docstr: return the observation k step away before.
docstr_tok: ["return","the","observation","k","step","away","before","."]
code: def k_step_observation(self, track: Dict):
      """return the observation k step away before."""
      obs_seqs = track.obs
      num_obs = len(obs_seqs)
      if num_obs == 0:
          return torch.tensor((-1, -1, -1, -1)).to(track.obs[0].device)
      elif num_obs > self.vel_delta_t:
          if obs_seqs[num_obs - 1 - self.vel_delta_t] is not None:
              return obs_seqs[num_obs - 1 - self.vel_delta_t]
          else:
              return self.last_obs(track)
      else:
          return self.last_obs(track)
  
imports: from typing import List, Optional, Tuple
  import numpy
  import torch
  from addict import Dict
  from mmengine.structures import InstanceData
  from mmdet.registry import MODELS
  from mmdet.structures import DetDataSample
  from mmdet.structures.bbox import bbox_cxcyah_to_xyxy, bbox_overlaps, bbox_xyxy_to_cxcyah
  from .sort_tracker import SORTTracker
label_desc: Use image node_id 7 for calling the OCSORTTracker obj's underlying member method code with example usage: obj.k_step_observation(track) and returns: torch, self, obs_seqs, self