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Problems publishing synchronized topics

asked 2015-03-19 07:03:39 -0500

aba92 gravatar image

I want to publish image synchronized topics using following code:

#include <message_filters/subscriber.h>
#include <message_filters/time_synchronizer.h>
#include <sensor_msgs/Image.h>
#include <sensor_msgs/CameraInfo.h>

using namespace sensor_msgs;
using namespace message_filters;

void callback(const ImageConstPtr& left_image, const CameraInfoConstPtr& left_cam_info, const ImageConstPtr& right_image, const CameraInfoConstPtr& right_cam_info)
  // Solve all of perception here...
    std::cout << "Time stamp (left image): "<< left_image->header.stamp << std::endl;
    std::cout << "Time stamp (right image): "<< right_image->header.stamp << std::endl;
    std::cout << "Time stamp (left camera info): "<< left_cam_info->header.stamp << std::endl;
    std::cout << "Time stamp (right camera info): "<< right_cam_info->header.stamp << std::endl;

int main(int argc, char** argv)
  ros::init(argc, argv, "vizzy_sync_node");

  ros::NodeHandle nh;

  message_filters::Subscriber<Image> left_image_sub(nh, "vizzy/left/image_raw", 1);
  message_filters::Subscriber<CameraInfo> left_info_sub(nh, "vizzy/left/camera_info", 1);
  message_filters::Subscriber<Image> right_image_sub(nh, "vizzy/right/image_raw", 1);
  message_filters::Subscriber<CameraInfo> right_info_sub(nh, "vizzy/right/camera_info", 1);

  TimeSynchronizer<Image, CameraInfo, Image, CameraInfo> sync(left_image_sub, left_info_sub, right_image_sub, right_info_sub, 10);
  sync.registerCallback(boost::bind(&callback, _1, _2, _3, _4));    // cria 4 callbacks


  return 0;

but I see that the Callback function is not fired and don't know why. Anyone can help me and if possible tell me if in order to output the synchronized topics I can just publish them with simple advertise?

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Are you sure the time stamps do EXACTLY match? The TimeSynchronizer requires this for firing the callback, no epsilon allowed....

Wolf gravatar image Wolf  ( 2015-03-19 08:33:21 -0500 )edit

1 Answer

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answered 2015-03-19 08:30:05 -0500

Chaos gravatar image

updated 2015-03-19 08:31:45 -0500

As far as I know you should specify the sychronization policy, i.e.

#include "message_filters/subscriber.h"
#include "message_filters/synchronizer.h"
#include "message_filters/time_synchronizer.h"
#include "message_filters/sync_policies/approximate_time.h"
#include <ros/callback_queue.h>
#include <boost/bind.hpp>

Furthermore you should set a callback queue.

Example: First:

using namespace message_filters;
ros::CallbackQueue my_callback_queue_;
message_filters::Subscriber<nav_msgs::Odometry> poseSub_;
message_filters::Subscriber<sensor_msgs::LaserScan> laserSub_;
typedef sync_policies::ApproximateTime<nav_msgs::Odometry, sensor_msgs::LaserScan> MySyncPolicy;
typedef message_filters::Synchronizer<MySyncPolicy> Synchronizer;
boost::shared_ptr<Synchronizer> sync_;

Specify the message_filter subscriber:

ros::NodeHandle nh_;
poseSub_.subscribe(nh_, "/robot_pose", 1);
laserSub_.subscribe(nh_, "/scan", 1);

Then set the synchronizer:

sync_.reset(new Synchronizer(MySyncPolicy(10), poseSub_, laserSub_));
sync_->registerCallback(boost::bind(&emergency_handler::avoid, this, _1, _2));

Then, in order to spin the callback:


The code I posted is intended for a class use.I hope this helped...

PS: Sorry for my poor English...

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Asked: 2015-03-19 07:03:39 -0500

Seen: 1,113 times

Last updated: Mar 19 '15