ROS1 vs ROS2 Comprehensive Comparison (1)

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Basic Architecture and Concepts

Feature ROS1 ROS2
Communication Middleware Custom TCPROS/UDPROS DDS (Data Distribution Service)
Master Node Required (roscore) No master needed (distributed discovery)
Operating Systems Primary: Ubuntu Linux
Limited: Windows, macOS		 Full support for Linux, Windows, macOS
Real-time Support Limited Improved with DDS and QoS policies
Multi-robot Systems Requires network configuration Native multi-domain support
Security Limited Built-in security with DDS (authentication, encryption)
Scalability Limited by single master Improved with distributed architecture

Package Management and Creation

Feature ROS1 ROS2
Package Creation Command catkin_create_pkg <pkg_name> [dependencies] ros2 pkg create --build-type ament_cmake/ament_python <pkg_name>
Package Structure (C++) CMakeLists.txt, package.xml, src/, include/ CMakeLists.txt, package.xml, src/, include/
Package Structure (Python) Same as C++, with Python files in scripts/ or src/ Different structure with setup.py, setup.cfg, Python modules in <pkg_name>/
Package XML Format Format 1 or 2 Format 3 (supports conditional dependencies)
Build System Catkin Ament
Build Command catkin_make or catkin build colcon build
Workspace Setup ~/catkin_ws/src, ~/catkin_ws/devel, ~/catkin_ws/build ~/ros2_ws/src, ~/ros2_ws/install, ~/ros2_ws/build
Source Workspace source ~/catkin_ws/devel/setup.bash source ~/ros2_ws/install/setup.bash

Nodes and Execution

Feature ROS1 ROS2
Node Creation (C++) Inherit from no class, use global NodeHandle Inherit from rclcpp::Node
Node Creation (Python) Import rospy, use global functions Import rclpy, inherit from rclpy.node.Node
Node Launch rosrun <pkg_name> <node_name> ros2 run <pkg_name> <node_name>
Node List Command rosnode list ros2 node list
Node Info Command rosnode info <node_name> ros2 node info <node_name>
Main Loop (C++) ros::spin() or ros::spinOnce() rclcpp::spin() or custom executor
Main Loop (Python) rospy.spin() rclpy.spin()
Execution Model Single-threaded or multi-threaded only Flexible executors (single-threaded, multi-threaded, custom)
Node Lifecycle Not supported natively Managed nodes with lifecycle states

Topics, Publishers, and Subscribers

Feature ROS1 ROS2
List Topics rostopic list ros2 topic list
Topic Info rostopic info <topic> ros2 topic info <topic>
Echo Topic rostopic echo <topic> ros2 topic echo <topic>
Publisher Creation (C++) ros::Publisher pub = nh.advertise<msg_type>("topic", queue_size) rclcpp::Publisher<msg_type>::SharedPtr pub = node->create_publisher<msg_type>("topic", qos)
Publisher Creation (Python) pub = rospy.Publisher("topic", msg_type, queue_size=10) pub = node.create_publisher(msg_type, "topic", qos_profile)
Subscriber Creation (C++) ros::Subscriber sub = nh.subscribe("topic", queue_size, callback) auto sub = node->create_subscription<msg_type>("topic", qos, callback)
Subscriber Creation (Python) sub = rospy.Subscriber("topic", msg_type, callback) sub = node.create_subscription(msg_type, "topic", callback, qos_profile)
Publishing Messages (C++) pub.publish(msg) pub->publish(msg)
Publishing Messages (Python) pub.publish(msg) pub.publish(msg)
Quality of Service Not supported Configurable QoS policies (reliability, durability, etc.)
Intra-process Communication Not supported natively Supported for optimized same-process communication
Topic Remapping Command line only rosrun pkg node _topic:=new_name Command line ros2 run pkg node --ros-args -r topic:=new_name

Services and Actions

Feature ROS1 ROS2
Service Creation (C++) ros::ServiceServer srv = nh.advertiseService("service", callback) rclcpp::Service<srv_type>::SharedPtr srv = node->create_service<srv_type>("service", callback)
Service Creation (Python) rospy.Service("service", srv_type, callback) node.create_service(srv_type, "service", callback)
Service Call (C++) ros::ServiceClient client = nh.serviceClient<srv_type>("service") rclcpp::Client<srv_type>::SharedPtr client = node->create_client<srv_type>("service")
Service Call (Python) rospy.ServiceProxy("service", srv_type) node.create_client(srv_type, "service")
List Services rosservice list ros2 service list
Call Service rosservice call <service> <args> ros2 service call <service> <srv_type> <args>
Actions Uses actionlib package Built-in rclcpp_action/rclpy.action

Parameters

Feature ROS1 ROS2
Parameter Server Centralized in master Distributed (each node has its own)
Set Parameter rosparam set <param> <value> ros2 param set <node> <param> <value>
Get Parameter rosparam get <param> ros2 param get <node> <param>
List Parameters rosparam list ros2 param list <node>
Parameter Files Load with rosparam load <file> Part of node configuration
Get Parameter (C++) nh.getParam("param", var) node->get_parameter("param", var) or node->declare_parameter("param", default_val)
Get Parameter (Python) rospy.get_param("param") node.get_parameter("param").value or node.declare_parameter("param", default_val)

Build Tools and Process

Feature ROS1 ROS2
Build System Catkin Ament
Build Tool catkin_make or catkin build colcon build
Package Dependencies <build_depend>, <run_depend> <build_depend>, <exec_depend>, <test_depend>, etc.
CMake Functions catkin_package(), add_executable() ament_package(), add_executable(), ament_target_dependencies()
Python Setup catkin_python_setup() Uses Python's setup.py
Install Rules Optional Required for all executables and libraries
Build Options Limited options with catkin Extensive options with colcon (symlink-install, packages-select, etc.)

Launch Files

Feature ROS1 ROS2
Format XML only Python, XML, or YAML
Launch Command roslaunch <pkg> <file>.launch ros2 launch <pkg> <file>.py/xml/yaml
Node Inclusion <node pkg="pkg" type="executable" name="name"/> XML: similar
Python: Node(package='pkg', executable='exec', name='name')
Arguments <arg name="arg" default="val"/> XML: similar
Python: DeclareLaunchArgument('arg', default_value='val')
Conditionals Limited XML conditionals Full programming language capabilities in Python launches
Include Files <include file="$(find pkg)/launch/file.launch"/> XML: similar
Python: IncludeLaunchDescription(...)

Data Recording and Playback (Bags)

Feature ROS1 ROS2
Command Tool rosbag ros2 bag
Record All Topics rosbag record -a ros2 bag record -a
Record Specific Topics rosbag record <topic1> <topic2> ros2 bag record <topic1> <topic2>
Play Bag File rosbag play <file>.bag ros2 bag play <path-to-bag-folder>
Info on Bag rosbag info <file>.bag ros2 bag info <path-to-bag-folder>
Storage Format Custom .bag files SQLite database by default, pluggable storage
Compression Limited options Multiple modes (file, message) and formats (zstd)
Splitting By size only By size or duration
Simulation Time Use with --clock Use with --use-sim-time
Playback Control Limited (start/stop) Services for pause, resume, seek, play at rate, etc.

Debugging and Analysis Tools

Feature ROS1 ROS2
Visualization RViz RViz2
Graph Visualization rqt_graph rqt_graph
Message Plotting rqt_plot rqt_plot
Console Logging rqt_console rqt_console
Topic Monitoring rostopic, rqt_topic ros2 topic, rqt_topic
Node Introspection rosnode ros2 node
Message Introspection rosmsg show ros2 interface show
Service Introspection rossrv show ros2 interface show
Diagnostics /diagnostics topic /diagnostics topic
Image Debugging image_view image_tools

Converting Between ROS1 and ROS2

Feature Description
ros1_bridge Package for connecting ROS1 and ROS2 systems
Message Compatibility Standard messages have equivalent types in both systems
Bridge Usage ros2 run ros1_bridge dynamic_bridge
Bridge Limitations Only works with message types known at compile time
Bridge Options --bridge-all-2to1-topics to bridge all ROS2 topics to ROS1

Additional ROS2 Features

Feature Description
Lifecycle Nodes Managed nodes with predefined states (unconfigured, inactive, active, etc.)
Components Dynamically loadable nodes that can use intra-process communications
QoS Settings Configure reliability, durability, history, and other communication properties
Multi-domain Support Run ROS2 nodes in different DDS domains for isolation
Security Authentication, encryption, and access control with SROS2

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