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How to solve "Timestamps of odometry and imu are x seconds apart"?

asked 2012-01-29 15:01:39 -0500

weiin gravatar image

updated 2012-01-30 17:32:25 -0500

I am getting the "Timestamps of odometry and imu are x seconds apart" problem listed in robot_pose_ekf troubleshooting. What are the possible ways to solve this?

I am currently publishing to /odom and /imu/data in two separate nodes. I notice that turtlebot publishes both in the same turtlebot_node. Is this the only way to get the two timestamps to sync?


EDIT (code snippets of publishing nodes, launch file uses the same robot_pose_ekf parameters found in turtlebot's minimal.launch)

for node publishing odometry:

  odom_pub = nh.advertise<nav_msgs::Odometry>("odom", 1);

...

void publish_odom(double x, double y, double theta)
{
// store the current pose
  prevPose.x = cur_x;
  prevPose.y = cur_y;
  prevPose.theta = cur_theta;
// calculate the new pose
  trobot.calcOdom(&cur_x,&cur_y,&cur_theta);

  current_time = ros::Time::now();
  double dt = (current_time - last_time).toSec();

  // convert rotation about z into quaternion
  geometry_msgs::Quaternion odom_quat;
  odom_quat.z=sin(cur_theta/2.0);
  odom_quat.w=cos(cur_theta/2.0);

  //next, we'll publish the odometry message over ROS
  nav_msgs::Odometry odom;
  odom.header.stamp = current_time;
  odom.header.frame_id = "odom";
  odom.child_frame_id = "base_footprint";

  //set the position
  odom.pose.pose.position.x = cur_x;
  odom.pose.pose.position.y = cur_y;
  odom.pose.pose.position.z = 0.0;
  odom.pose.pose.orientation = odom_quat;
  odom.pose.covariance = 
        boost::array<double, 36>{{1e-3, 0, 0, 0, 0, 0, 
                                0, 1e-3, 0, 0, 0, 0,
                                0, 0, 1e6, 0, 0, 0,
                                0, 0, 0, 1e6, 0, 0,
                                0, 0, 0, 0, 1e6, 0,
                                0, 0, 0, 0, 0, 1e-3}};

  //set the velocity
  odom.twist.twist.linear.x = (cur_x-prevPose.x)/dt;
  odom.twist.twist.linear.y = (cur_y-prevPose.y)/dt;
  odom.twist.twist.angular.z = (cur_theta-prevPose.theta)/dt;
  odom.twist.covariance = 
        boost::array<double, 36>{{1e-3, 0, 0, 0, 0, 0, 
                                0, 1e-3, 0, 0, 0, 0,
                                0, 0, 1e6, 0, 0, 0,
                                0, 0, 0, 1e6, 0, 0,
                                0, 0, 0, 0, 1e6, 0,
                                0, 0, 0, 0, 0, 1e-3}};

  //publish the message
  odom_pub.publish(odom);
  last_time = current_time;
}

And for the imu (covariance values defined in initialisation):

imu_data_pub_ = imu_node_handle.advertise<sensor_msgs::Imu>("data", 100);

...

void publish_imu_data()
{
    // get gyro-stabilized quaternion, instantaneous acceleration and bias-compensated angular rate
    if(imu.ReadQuatVect(comPort, quaternion, accel, angRate))
    {

    // convert North-East-Down (NED) to East-North-Up (ENU) coordinates
        imu_data.orientation.w = quaternion.w;
        imu_data.orientation.x = quaternion.y;
        imu_data.orientation.y = quaternion.x;
        imu_data.orientation.z = -quaternion.z;

        imu_data.linear_acceleration.x = accel.y;
        imu_data.linear_acceleration.y = accel.x;
        imu_data.linear_acceleration.z = -accel.z;

        imu_data.angular_velocity.x = angRate.y;
        imu_data.angular_velocity.y = angRate.x;
        imu_data.angular_velocity.z = -angRate.z;

        if(errcnt>0) errcnt--;

        imu_data.header.stamp = ros::Time::now();
        imu_data.header.frame_id = "gyro_link";
        imu_data_pub_.publish(imu_data);
    }
    else errcnt++;

    // removed: code to handle large errcnt 
}
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Comments

How often are you calling these callbacks? Can you put a ROS_INFO into each printing the timestamp each time it publishes and show the result?
tfoote gravatar imagetfoote ( 2012-01-31 03:46:47 -0500 )edit
well. I'm not able to get the error message anymore, even after trying different callback rates (up to the max that my imu can handle). perhaps the system restart overnight did the trick...
weiin gravatar imageweiin ( 2012-02-02 11:19:48 -0500 )edit

1 Answer

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answered 2012-01-29 18:14:28 -0500

this post is marked as community wiki

This post is a wiki. Anyone with karma >75 is welcome to improve it.

It is not required to publish them from the same node. From the link:

"This error occurs when the timestamps of the sensor messages that are received differ more than 1 second. This is probably an indication of timing issues in your system, e.g. the clocks of two hosts connected to the same ros core are not synchronized."

The most common cause of this is that you're running on 2 or more computers and their system clocks are out of sync by x seconds. It's recommended to setup ntp servers to keep all computers in sync.

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Comments

The problem is that I am getting this out of sync message even though I'm running everything on the same laptop (the ASUS that came with turtlebot)
weiin gravatar imageweiin ( 2012-01-29 19:06:37 -0500 )edit
You should check how your nodes are setting their timestamps. If you want more help you will need to provide more information. Code snippets, and error messages verbatim.
tfoote gravatar imagetfoote ( 2012-01-30 08:52:56 -0500 )edit
I have posted the codes from the two nodes. But I am not currently able to reproduce the same error message all the time (it is basically the "[ERROR]... Timestamps of ... are x seconds apart" with x being something more than 1.0). I'm not sure if it matters, but my odom publisher publishes to /odom
weiin gravatar imageweiin ( 2012-01-30 17:37:01 -0500 )edit
and with robot_pose_ekf using output_frame="odom", will it affect how things work?
weiin gravatar imageweiin ( 2012-01-30 17:38:12 -0500 )edit
The frame /odom and the topic /odom are not related and won't affect each other.
raahlb gravatar imageraahlb ( 2012-01-30 18:32:30 -0500 )edit

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Asked: 2012-01-29 15:01:39 -0500

Seen: 1,765 times

Last updated: Jan 30 '12