ros_msgs_sync

A couple utils to ease ros messages synchronization using the message_filters::Synchronizer

Package Summary

Provides a template class MessageSynchronizerBase which automically register and setup the whole pipeline used by message_filters::Synchronizer by means of nasty metaprogramming.

The MessageSynchronizerBase can be used as a standalone or else by inheriting from MessageSynchronizerBase<my-list-of-msg-type> one only has to overload the virtual function callback() to manage to synchronized callback messages.

• Maintainer status: maintained
• Maintainer: name deray.jeremie@gmail.com
• Author: name deray.jeremie@gmail.com
• License: APACHE-2.0
• Bug / feature tracker: https://github.com/artivis/ros_msgs_sync/issues
• Source: git https://github.com/artivis/ros_msgs_sync (branch: master)

Quick Start

Installation

Binaries

todo...
#$ apt-get install ros-indigo-my-package

From source

$ git clone https://github.com/artivis/ros_msgs_sync
$ catkin build ros_msgs_sync

Demo Example

The file example/demo_synchronizer.cpp together with it's launch file shows how one can use one of the synchronizer available with this package. The demo synchronizes 2 sensor_msgs::Image and 2 sensor_msgs::CameraInfo messages.

$ roslaunch ros_msgs_sync demo_synchronizer.launch

Documentation and Tutorials

As a minimal example, we will synchronize a sensor_msgs::Image with an associated sensor_msgs::Camera :

#include "ros_msgs_sync/ros_msgs_sync.h"
#include <ros/ros.h>

/// Typef the synchronizer
/// Template arguments
/// 1. synchronization policy
/// 2-9. message types to be synchronized
using MySync =
  ros_msgs_sync::MessageSynchronizerBase<message_filters::sync_policies::ApproximateTime,
                                         sensor_msgs::Image, sensor_msgs::CameraInfo>;

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

  std::size_t image_queue = 5;
  std::size_t camera_info_queue = 5;

  MySync msg_sync(image_queue, camera_info_queue);

  msg_sync.start();

  sensor_msgs::ImageConstPtr image;
  sensor_msgs::CameraInfoConstPtr cam_info;

  while (ros::ok())
  {
    std::tie(image, cam_info) = msg_sync.getMessage();

    // Do stuff with messages.

    ros::spinOnce();
  }

  return EXIT_SUCCESS;
}

That's it !

For more details, an example is available in the example folder of the package together with its launch file.

Notice

Topics :

Subscribers are listening to the topics :

• ~synchronized_topic_0
• ~synchronized_topic_1
• ...
• ~synchronized_topic_N

thus they need to be remapped, e.g. from a launch file

<remap from="~synchronized_topic_0" to="my_camera_topic"/>

Subscribers :

The class automatically instantiate a image_transport::SubscriberFilter for image messages - configurable through a ImageSubcriberParameters - while uses a message_filters::Subscriber for any other message types - configurable through a SubcriberParameters.

More configuration

#include "ros_msgs_sync/ros_msgs_sync.h"
#include <ros/ros.h>

/// Typef the synchronizer
/// Template arguments
/// 1. synchronization policy
/// 2-9. message types to be synchronized
using MySync =
  ros_msgs_sync::MessageSynchronizerBase<message_filters::sync_policies::ApproximateTime,
                                         sensor_msgs::Image, sensor_msgs::CameraInfo>;

int main(int argc, char** argv)
{
  // See image_transport::TransportHints documentation for more information.
  image_transport::TransportHints image_transport_hints;

  ros_msgs_sync::ImageSubcriberParameters image_sub_params;
  image_sub_params.queue_size = 5;
  image_sub_params.transport_hints = image_transport_hints;

  // See ros::TransportHints documentation for more information.
  ros::TransportHints transport_hints;

  MySync camera_info_sub_params;
  camera_info_sub_params.queue_size = 5;
  camera_info_sub_params.transport_hints = transport_hints;
  camera_info_sub_params.callback_queue = nullptr;

  ros_msgs_sync::SyncApproxImagesWithInfo msg_sync(image_sub_params, camera_info_sub_params);

  // Set the callback queue size of the synchronizer.
  msg_sync.setSyncQueueSize(5);

  msg_sync.start();

  ...

  // subscribers parameters may be changed later on.
  msg_sync.setQueueSize<0>(10);
  msg_sync.getSubscriberParameters<1>().queue_size = 10;

  // However one need to stop/start the synchronizer
  // for the change to take effects

  msg_sync.restart();

  ...

  return EXIT_SUCCESS;
}

Pre-defined synchronizers

The header ros_msgs_sync.h defines the following useful synchronizer:

SyncApprox2Images;
SyncApproxNImages; // Where N is in [2 - 9]

SyncApproxImagesWithInfo;  // Sync sensor_msgs::Image + sensor_msgs::CameraInfo
SyncApprox2ImagesWithInfo; // Sync sensor_msgs::Image + sensor_msgs::CameraInfo X 2
SyncApprox3ImagesWithInfo; // Sync sensor_msgs::Image + sensor_msgs::CameraInfo X 3
SyncApprox4ImagesWithInfo; // Sync sensor_msgs::Image + sensor_msgs::CameraInfo X 4

SyncExactImagesWithInfo; // Sync sensor_msgs::Image + sensor_msgs::CameraInfo

Notice the following helper types:

MessageSynchronizerApprox<MsgType0, MsgType1, etc...>;

MessageSynchronizerExact<MsgType0, MsgType1, etc...>;

Contributing

Please, feel free.