Simulation time and bag operation in ROS

ROS Time type

ROS There are two kinds of time ：

ROS::Time[/Duration/Rate]：ROS Time —— Sources can be considered as modifications such as acceleration / Slow down / Pause .
ROS::WallTime[WallDuration/WallRate]：ROS Absolute time —— Immutable " real " Time .

be-all ros::node If there is a setting at startup [ros::param] \use_sim_time = true The of the node ROS::Time from /clock In order to get , Otherwise, its value and ROS::WallTime Agreement .

Observe the phenomenon ：

stay ROS_INFO The difference between the two can be observed in the output timestamp . First we set up rosparam set /use_sim_time true Then start the following code :

ROS_INFO("%lf,%lf",(double)(ros::WallTime::now().toSec()),
                   (double)(ros::Time::now().toSec()));

Input :rostopic pub /clock rosgraph_msgs/Clock "clock: secs: 1 nsecs: 0" Then run the above code

Input :rosparam delete /use_sim_time Rerun code

use

ROS Time and time stamp stamp Yes, some rosnode It's crucial ：

such as rviz and tf Will msg Of header/stamp And rosnode Current time comparison to discard invalid data (OLD_DATA).
ActionClient The current time will be automatically added to stamp Send to ActionServer, and ActionSerer Will compare the new msg And history msg Of stamp To determine whether it is legal data .

Recording rosbag When msg/header/stamp The timestamp is the value of the recording time . May cause the current ROS Time A mismatch with the timestamp results in ： Throw an exception , What's more, the direct function is abnormal .

We can set use_sim_time Restart node , change ROS Time source . And through the rosbag ... --clock Parameter let rosbag Release /clock drive ROS Time