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https://github.com/artivis/ros_msgs_sync

[ROS] synchronises msgs
https://github.com/artivis/ros_msgs_sync

c-plus-plus message-synchronization robotics ros

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[ROS] synchronises msgs

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# ros_msgs_sync

## A couple utils to ease ros messages synchronization using the [`message_filters::Synchronizer`](http://wiki.ros.org/message_filters#Policy-Based_Synchronizer_.5BROS_1.1.2B-.5D)



## Package Summary

Provides a template class `MessageSynchronizerBase` which automically register and setup the whole pipeline

used by [`message_filters::Synchronizer`](http://wiki.ros.org/message_filters#Policy-Based_Synchronizer_.5BROS_1.1.2B-.5D) by

means of nasty metaprogramming.



The `MessageSynchronizerBase` can be used as a standalone or else by

inheriting from `MessageSynchronizerBase` one only has to overload

the virtual function `callback()` to manage to synchronized callback messages.



-   Maintainer status: maintained

-   Maintainer: name 

-   Author: name 

-   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)



[![Build Status](https://travis-ci.org/artivis/ros_msgs_sync.svg?branch=master)](https://travis-ci.org/artivis/ros_msgs_sync)

---



## Quick Start



### Installation



#### Binaries

```terminal

todo...

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

```



#### From source

```terminal

$ 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.



```terminal

$ 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` :

```cpp

#include "ros_msgs_sync/ros_msgs_sync.h"

#include 



/// Typef the synchronizer

/// Template arguments

/// 1. synchronization policy

/// 2-9. message types to be synchronized

using MySync =

  ros_msgs_sync::MessageSynchronizerBase;



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

```xml



```



##### 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



```cpp

#include "ros_msgs_sync/ros_msgs_sync.h"

#include 



/// Typef the synchronizer

/// Template arguments

/// 1. synchronization policy

/// 2-9. message types to be synchronized

using MySync =

  ros_msgs_sync::MessageSynchronizerBase;



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:



```cpp

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:  



```cpp

MessageSynchronizerApprox;



MessageSynchronizerExact;

```



## Contributing



Please, feel free.