ROS Synchronization Example

CMakeLists.txt

cmake_minimum_required(VERSION 2.8.3)
project(sync_example)

find_package(catkin REQUIRED COMPONENTS message_filters roscpp sensor_msgs)

catkin_package(
  CATKIN_DEPENDS message_filters roscpp sensor_msgs
)

include_directories(${catkin_INCLUDE_DIRS})

add_executable(sync_example src/sync_example.cpp)
target_link_libraries(sync_example ${catkin_LIBRARIES})

package.xml

<package format="2">
  <name>sync_example</name>
  <version>0.0.1</version>
  <description>
    Approximate time sync example.
  </description>
  <author>Thomas Denewiler</author>
  <maintainer email="tdenewiler@gmail.com">Thomas Denewiler</maintainer>
  <license>BSD</license>
  <url>https://github.com/tdenewiler/sync_example</url>

  <buildtool_depend>catkin</buildtool_depend>

  <depend>message_filters</depend>
  <depend>roscpp</depend>
  <depend>sensor_msgs</depend>
</package>

sync_example.cpp

#include <ros/ros.h>
#include <sensor_msgs/Image.h>
#include <message_filters/subscriber.h>
#include <message_filters/synchronizer.h>
#include <message_filters/sync_policies/approximate_time.h>


class Node
{
 public:
  Node()
  {
    sub_1_.subscribe(nh_, "in1", 1);
    sub_2_.subscribe(nh_, "in2", 1);
    sync_.reset(new Sync(MySyncPolicy(10), sub_1_, sub_2_));
    sync_->registerCallback(boost::bind(&Node::callback, this, _1, _2));
  }

  void callback(const sensor_msgs::ImageConstPtr &in1, const sensor_msgs::ImageConstPtr &in2)
  {
    ROS_INFO("Synchronization successful");
  }

 private:
  ros::NodeHandle nh_;
  message_filters::Subscriber<sensor_msgs::Image> sub_1_;
  message_filters::Subscriber<sensor_msgs::Image> sub_2_;

  typedef message_filters::sync_policies::ApproximateTime<sensor_msgs::Image, sensor_msgs::Image> MySyncPolicy;
  typedef message_filters::Synchronizer<MySyncPolicy> Sync;
  boost::shared_ptr<Sync> sync_;
};

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

  Node synchronizer;

  ros::spin();
}