void TebLocalPlannerROS::configureBackupModes(
    std::vector<geometry_msgs::PoseStamped>& transformed_plan,  
    int& goal_idx)
{
    ros::Time current_time = ros::Time::now();
    // reduced horizon backup mode  上篇博客所列的第四种情况下

    // we do not reduce if the goal is already selected , because the orientation 
    // might change -> can introduce oscillations
    // no_infeasible_plans_  改成 no_feasible_plans_ 比较合适
    if (cfg_.recovery.shrink_horizon_backup && 
        goal_idx < (int)transformed_plan.size()-1 && 
       (no_infeasible_plans_>0 || (current_time - time_last_infeasible_plan_).toSec() < 
         // keep short horizon for at least a few seconds
         cfg_.recovery.shrink_horizon_min_duration )  ) 
    {
        ROS_INFO_COND(no_infeasible_plans_==1, 
        "Activating reduced horizon backup mode for at least %.2f sec (infeasible 
        trajectory detected).", 
        cfg_.recovery.shrink_horizon_min_duration);

        // Shorten horizon if requested     reduce to 50 percent:
        int horizon_reduction = goal_idx/2;
        
        if (no_infeasible_plans_ > 9)
        {
            ROS_INFO_COND(no_infeasible_plans_==10, "Infeasible trajectory detected 
                10 times in a row: further reducing horizon...");
            horizon_reduction /= 2;
        }
        // we have a small overhead (过头) here, since we already transformed 50% 
        // more of the trajectory.  But that's ok for now, since we do not 
        // need to make   transformGlobalPlan   more complex
        // reduced horizon 应当很少发生
        int new_goal_idx_transformed_plan = int(transformed_plan.size()) - horizon_reduction - 1;
        goal_idx -= horizon_reduction;

        // 从 transformed_plan 的 new_goal_idx 开始，一直删除到尾部
        if (new_goal_idx_transformed_plan >0  &&  goal_idx >= 0)
            transformed_plan.erase(transformed_plan.begin() + new_goal_idx_transformed_plan, transformed_plan.end());
        else
            goal_idx += horizon_reduction; // this should not happen, but safety first
    }
                // ......第二部分......
}

• shrink_horizon_backup: true. 在自动检测到问题(plan not feasible)的情况下，允许planner临时缩小范围(50%). TEB将以更近的点作为规划目标，尝试重新规划出可行路径。调试时可关闭，以在可视化界面上观察原出错路径。另请参阅参数shrink_horizo​​n_min_duration

• shrink_horizon_min_duration: 10，单位秒。 如果检测到不可行的轨迹，激活缩小的水平线后备模式，本参数为其最短持续时间。个人怀疑这个参数无意义，因为它更新值的地方也都有no_infeasible_plans_变量的更新，判断时，只根据no_infeasible_plans_即可，详见代码configureBackupModes