有一次机器人没有装雷达和相机，打算随便跑跑。于是在通用代价地图的障碍层，不设置传感器数据来源，运行move_base出现频繁报警

The /scan observation buffer has not been updated for 22.06 seconds, and it should be updated every 5.00 seconds.

来源在

bool ObservationBuffer::isCurrent() const
{
  if (expected_update_rate_ == ros::Duration(0.0))
    	return true;
  // last_updated_ 没有赋值
  bool current = (ros::Time::now() - last_updated_).toSec() <= expected_update_rate_.toSec();
  if (!current)
  {
    ROS_WARN(
        "The %s observation buffer has not been updated for %.2f seconds, and it should be updated every %.2f seconds.",
        topic_name_.c_str(), (ros::Time::now() - last_updated_).toSec(), expected_update_rate_.toSec());
  }
  return current;
}

此时发导航命令，又有报警

[/move_base]:Sensor data is out of date, we're not going to allow commanding of the base for safety

因为没有可靠的传感器数据，move_base不允许车跑起来。来源在MoveBase::executeCycle

if(!controller_costmap_ros_->isCurrent())
{
  ROS_WARN("[%s]:Sensor data is out of date, we're not going to allow commanding of the base for safety",ros::this_node::getName().c_str());
  publishZeroVelocity();
  return false;
}

也就是函数

bool LayeredCostmap::isCurrent()
{
  current_ = true;
  for (vector<boost::shared_ptr<Layer> >::iterator plugin = plugins_.begin(); plugin != plugins_.end();
      ++plugin)
  {
    current_ = current_ && (*plugin)->isCurrent();
  }
}

显然是因为障碍层不符合isCurrent，导致代价地图也不符合isCurrent。如果希望车照样跑，就把MoveBase::executeCycle那段注释掉，把ObservationBuffer::isCurrent()的报警也注释掉，否则没完没了。

从网上下载一个包含雷达数据的bag，又设置了通用代价地图和tf树后，发现报警依然，应该还是时间戳问题，懒得再对齐了。