State of ROS 2

Publish / Subscribe

Source code of the listener (ROS 1)

void callback(const std_msgs::String::ConstPtr & msg)
{
  ROS_INFO("I heard: [%s]", msg->data.c_str());
}

int main(int argc, char * argv[])
{
  ros::init(argc, argv, "listener");

  ros::NodeHandle node;

  ros::Subscriber sub = node.subscribe("chatter", 10, callback);

  ros::spin();

  return 0;
}
 
 
 
 
 
 
 
            

Source code of the listener (ROS 1)

// void callback(const std_msgs::String::ConstPtr & msg)

{
  // ROS_INFO("I heard: [%s]", msg->data.c_str());

}

int main(int argc, char * argv[])
{
  // ros::init(argc, argv, "listener");


  // ros::NodeHandle node;


  // ros::Subscriber sub = node.subscribe("chatter", 10, callback);



  // ros::spin();


  return 0;
}
            

Source code of the listener (ROS 2)

// void callback(const std_msgs::String::ConstPtr & msg)
void callback(std_msgs::msg::String::ConstSharedPtr msg)
{
  // ROS_INFO("I heard: [%s]", msg->data.c_str());
  printf("I heard: [%s]\n", msg->data.c_str());
}

int main(int argc, char * argv[])
{
  // ros::init(argc, argv, "listener");
  rclcpp::init(argc, argv);

  // ros::NodeHandle node;
  auto node = rclcpp::Node::make_shared("listener");

  // ros::Subscriber sub = node.subscribe("chatter", 10, callback);
  auto sub = node->create_subscription<std_msgs::msg::String>(
    "chatter", rmw_qos_profile_default, callback);

  // ros::spin();
  rclcpp::spin(node);

  return 0;
}
            

C++11 wherever it makes it easier,
the callback can be a lambda.

The node's name is passed
to the node constructor,
not the global init() function.

The subscriber is templated on the message type.

spin() is called on the node,
not globally.

DDS vendors

Company and product name		License	RMW impl.	Comments
	RTI Connext	commercial, research		stat. & dyn. impl.
	PrismTech OpenSplice	commercial, LGPL		only version 6.4 is LGPL
	TwinOaks CoreDX	commercial
	eProsima FastRTPS	LGPL		no support for fragmentation yet
	OSRF FreeRTPS	Apache 2	partial	small part of DDS only aiming for emb. devices

Inter Process Publish / Subscribe

Intra Process Publish / Subscribe

The networking spectrum

Some of the QoS settings

• ROS1: UDPROS/TCPROS ROS2: Reliability
  • Best effort: messages arrive “on time“
    at the expense of losing some
  • Reliable: all messages must reach the other end
• ROS1: Queueing ROS2: History
  • Keep last: only store N messages,
    configurable with queue depth option
  • Keep all: store all messages
• ROS1: Latching ROS2: Durability
  • Volatile: no persistence
  • Transient local: durable data is maintained by the writer
• Much richer spectrum of QoS capabilities with ROS2

DDS provides QoS “for free”

• Industry-proven QoS strategies
  • Extensive DDS documentation
  • Shared knowledge
  • Frees us from implementing a complex custom solution
  
  
• Using UDP (instead of TCP) allows multicasting
  • Publisher won't have to transmit extra copies of a message to every subscriber


• Support unreliable networks, e.g. drones, IoT, high latency links

QoS profiles

typedef struct RMW_PUBLIC_TYPE rmw_qos_profile_t
{
  enum rmw_qos_history_policy_t history;
  size_t depth;
  enum rmw_qos_reliability_policy_t reliability;
  enum rmw_qos_durability_policy_t durability;
} rmw_qos_profile_t;
            

Bridging between ROS versions

Dynamic Bridge