ROS1 Development Skill

When to Use This Skill

Building or maintaining ROS1 packages and nodes
Writing launch files, message types, or services
Debugging ROS1 communication (topics, services, actions)
Configuring catkin workspaces and build systems
Working with tf/tf2 transforms, URDF, or robot models
Using actionlib for long-running tasks
Optimizing nodelets for zero-copy transport
Planning ROS1 → ROS2 migration

Core Architecture Principles

1. Node Design

Single Responsibility Nodes: Each node should do ONE thing well. Resist the temptation to build monolithic "do-everything" nodes.

# BAD: Monolithic node
class RobotNode:
    def __init__(self):
        self.sub_camera = rospy.Subscriber('/camera/image', Image, self.camera_cb)
        self.sub_lidar = rospy.Subscriber('/lidar/points', PointCloud2, self.lidar_cb)
        self.pub_cmd = rospy.Publisher('/cmd_vel', Twist, queue_size=10)
        self.pub_map = rospy.Publisher('/map', OccupancyGrid, queue_size=1)
        # This node does perception, planning, AND control

# GOOD: Decomposed nodes
class PerceptionNode:    # Fuses sensor data → publishes /obstacles
class PlannerNode:       # Subscribes /obstacles → publishes /path
class ControllerNode:    # Subscribes /path → publishes /cmd_vel

Node Initialization Pattern:

#!/usr/bin/env python
import rospy
from std_msgs.msg import String

class MyNode:
    def __init__(self):
        rospy.init_node('my_node', anonymous=False)

        # 1. Load parameters FIRST
        self.rate = rospy.get_param('~rate', 10.0)
        self.frame_id = rospy.get_param('~frame_id', 'base_link')

        # 2. Set up publishers BEFORE subscribers
        #    (prevents callbacks firing before publisher is ready)
        self.pub = rospy.Publisher('~output', String, queue_size=10)

        # 3. Set up subscribers LAST
        self.sub = rospy.Subscriber('~input', String, self.callback)

        rospy.loginfo(f"[{rospy.get_name()}] Initialized with rate={self.rate}")

    def callback(self, msg):
        # Process and republish
        result = String(data=msg.data.upper())
        self.pub.publish(result)

    def run(self):
        rate = rospy.Rate(self.rate)
        while not rospy.is_shutdown():
            # Periodic work here
            rate.sleep()

if __name__ == '__main__':
    try:
        node = MyNode()
        node.run()
    except rospy.ROSInterruptException:
        pass

2. Topic Design

Naming Conventions:

/robot_name/sensor_type/data_type

# Examples:
/ur5/joint_states              # Robot joint states
/realsense/color/image_raw     # Camera color image
/realsense/depth/points        # Depth point cloud
/mobile_base/cmd_vel           # Velocity commands
/gripper/command               # Gripper commands

Queue Sizes Matter:

# For sensor data (high frequency, OK to drop old messages):
rospy.Subscriber('/camera/image', Image, self.cb, queue_size=1)

# For commands (don't want to miss any):
rospy.Publisher('/cmd_vel', Twist, queue_size=10)

# For large data (point clouds, images) - use small queues to prevent memory bloat:
rospy.Subscriber('/lidar/points', PointCloud2, self.cb, queue_size=1)

# NEVER use queue_size=0 (infinite) for high-frequency topics
# This WILL cause memory leaks under load

Latched Topics for data that changes infrequently:

# Robot description, static maps, calibration data
pub = rospy.Publisher('/robot_description', String, queue_size=1, latch=True)

3. Launch File Best Practices

<launch>
  <!-- ALWAYS use args for configurability -->
  <arg name="robot_name" default="ur5"/>
  <arg name="sim" default="false"/>
  <arg name="debug" default="false"/>

  <!-- Group by subsystem with namespaces -->
  <group ns="$(arg robot_name)">

    <!-- Conditional loading based on sim vs real -->
    <group if="$(arg sim)">
      <include file="$(find my_pkg)/launch/sim_drivers.launch"/>
    </group>
    <group unless="$(arg sim)">
      <include file="$(find my_pkg)/launch/real_drivers.launch"/>
    </group>

    <!-- Node with proper remapping -->
    <node pkg="my_pkg" type="perception_node.py" name="perception"
          output="screen" respawn="true" respawn_delay="5">
      <param name="rate" value="30.0"/>
      <param name="frame_id" value="$(arg robot_name)_base_link"/>
      <remap from="~input_image" to="/$(arg robot_name)/camera/image_raw"/>
      <remap from="~output_detections" to="detections"/>
      <!-- Load a YAML param file -->
      <rosparam file="$(find my_pkg)/config/perception.yaml" command="load"/>
    </node>

  </group>

  <!-- Debug tools (conditionally loaded) -->
  <group if="$(arg debug)">
    <node pkg="rviz" type="rviz" name="rviz"
          args="-d $(find my_pkg)/rviz/debug.rviz"/>
    <node pkg="rqt_graph" type="rqt_graph" name="rqt_graph"/>
  </group>
</launch>

4. TF Transform Tree

Rules:

Every frame has EXACTLY one parent (tree, not graph)
Static transforms use static_transform_publisher
Dynamic transforms publish at consistent rates
ALWAYS set timestamps correctly

import tf2_ros

# Publishing transforms
br = tf2_ros.TransformBroadcaster()
t = TransformStamped()
t.header.stamp = rospy.Time.now()  # CRITICAL: Use current time
t.header.frame_id = "odom"
t.child_frame_id = "base_link"
t.transform.translation.x = x
t.transform.translation.y = y
t.transform.rotation = quaternion_from_euler(0, 0, theta)
br.sendTransform(t)

# Listening for transforms (with timeout and exception handling)
tf_buffer = tf2_ros.Buffer()
listener = tf2_ros.TransformListener(tf_buffer)

try:
    trans = tf_buffer.lookup_transform(
        'map', 'base_link',
        rospy.Time(0),          # Get latest available
        rospy.Duration(1.0)     # Wait up to 1 second
    )
except (tf2_ros.LookupException,
        tf2_ros.ConnectivityException,
        tf2_ros.ExtrapolationException) as e:
    rospy.logwarn(f"TF lookup failed: {e}")

5. Actionlib for Long-Running Tasks

import actionlib
from my_msgs.msg import PickPlaceAction, PickPlaceGoal, PickPlaceResult

# Server
class PickPlaceServer:
    def __init__(self):
        self.server = actionlib.SimpleActionServer(
            'pick_place',
            PickPlaceAction,
            execute_cb=self.execute,
            auto_start=False  # ALWAYS set auto_start=False
        )
        self.server.start()

    def execute(self, goal):
        feedback = PickPlaceFeedback()

        # Check for preemption INSIDE your loop
        for step in self.plan_steps(goal):
            if self.server.is_preempt_requested():
                self.server.set_preempted()
                return
            self.execute_step(step)
            feedback.progress = step.progress
            self.server.publish_feedback(feedback)

        result = PickPlaceResult(success=True)
        self.server.set_succeeded(result)

Common Pitfalls & Failure Modes

Time Synchronization

# BAD: Comparing timestamps from different clocks
if camera_msg.header.stamp == lidar_msg.header.stamp:  # Almost never true

# GOOD: Use message_filters for approximate time sync
import message_filters
sub_cam = message_filters.Subscriber('/camera/image', Image)
sub_lidar = message_filters.Subscriber('/lidar/points', PointCloud2)
sync = message_filters.ApproximateTimeSynchronizer(
    [sub_cam, sub_lidar], queue_size=10, slop=0.05  # 50ms tolerance
)
sync.registerCallback(self.synced_callback)

Callback Threading

# ROS1 uses a single-threaded spinner by default.
# Long-running callbacks BLOCK all other callbacks.

# BAD:
def callback(self, msg):
    result = self.expensive_computation(msg)  # Blocks for 2 seconds!
    self.pub.publish(result)

# GOOD: Use a MultiThreadedSpinner or process in a separate thread
rospy.init_node('my_node')
# ... setup ...
spinner = rospy.MultiThreadedSpinner(num_threads=4)
spinner.spin()

# Or use a processing thread:
import threading, queue
class MyNode:
    def __init__(self):
        self.work_queue = queue.Queue(maxsize=1)
        self.worker = threading.Thread(target=self._process_loop, daemon=True)
        self.worker.start()

    def callback(self, msg):
        try:
            self.work_queue.put_nowait(msg)  # Non-blocking
        except queue.Full:
            pass  # Drop old data

    def _process_loop(self):
        while not rospy.is_shutdown():
            msg = self.work_queue.get()
            result = self.expensive_computation(msg)
            self.pub.publish(result)

Parameter Server Anti-Patterns

# BAD: Hardcoded values
self.threshold = 0.5

# BAD: Global params without namespace
self.threshold = rospy.get_param('threshold', 0.5)  # Collides across nodes

# GOOD: Private params with defaults
self.threshold = rospy.get_param('~threshold', 0.5)

# GOOD: Dynamic reconfigure for runtime tuning
from dynamic_reconfigure.server import Server
from my_pkg.cfg import MyNodeConfig
self.dyn_server = Server(MyNodeConfig, self.dyn_callback)

Nodelets for Zero-Copy Transport

When nodes exchange large data (images, point clouds) within the same process, nodelets eliminate serialization overhead:

// my_nodelet.h
#include <nodelet/nodelet.h>
#include <pluginlib/class_list_macros.h>

class MyNodelet : public nodelet::Nodelet {
  virtual void onInit() {
    ros::NodeHandle& nh = getNodeHandle();
    ros::NodeHandle& pnh = getPrivateNodeHandle();
    // Use shared_ptr for zero-copy: pass pointers, not copies
    pub_ = nh.advertise<sensor_msgs::Image>("output", 1);
    sub_ = nh.subscribe("input", 1, &MyNodelet::callback, this);
  }
};
PLUGINLIB_EXPORT_CLASS(MyNodelet, nodelet::Nodelet)

Package Structure

my_robot_pkg/
├── CMakeLists.txt
├── package.xml
├── setup.py                    # For Python packages
├── config/
│   ├── robot_params.yaml       # Default parameters
│   └── dynamic_reconfigure/    # .cfg files
├── launch/
│   ├── robot.launch            # Top-level launcher
│   ├── drivers.launch          # Hardware drivers
│   └── perception.launch       # Perception pipeline
├── msg/                        # Custom message definitions
│   └── Detection.msg
├── srv/                        # Service definitions
│   └── GetPose.srv
├── action/                     # Action definitions
│   └── PickPlace.action
├── src/                        # C++ source
│   └── my_node.cpp
├── scripts/                    # Python nodes (executable)
│   └── perception_node.py
├── include/my_robot_pkg/       # C++ headers
│   └── my_node.h
├── rviz/                       # RViz configs
│   └── debug.rviz
├── urdf/                       # Robot model
│   └── robot.urdf.xacro
└── test/                       # Unit and integration tests
    ├── test_perception.py
    └── test_perception.test    # rostest launch file

Debugging Toolkit

# Essential diagnostic commands
rostopic list                     # See all active topics
rostopic hz /camera/image_raw     # Check publish rate
rostopic bw /lidar/points         # Check bandwidth
rostopic echo /joint_states -n 1  # Inspect one message

rosnode list                      # Active nodes
rosnode info /perception          # Connections and subscriptions

roswtf                            # Automated diagnostics

rqt_graph                         # Visual node/topic graph
rqt_console                       # Log viewer with filtering

# TF debugging
rosrun tf tf_monitor              # Monitor TF tree health
rosrun tf view_frames             # Generate TF tree PDF
rosrun tf tf_echo map base_link   # Print transform continuously

# Bag file operations
rosbag record -a                  # Record everything (careful with disk!)
rosbag record /camera/image /tf   # Record specific topics
rosbag info recording.bag         # Inspect bag contents
rosbag play recording.bag --clock # Playback with simulated time

ROS1 → ROS2 Migration Checklist

When planning a migration, note these key differences:

rospy → rclpy, roscpp → rclcpp
catkin_make → colcon build
roslaunch XML → ROS2 Python launch files
Global parameter server → Per-node parameters
rospy.Rate → node.create_timer()
Single roscore → DDS discovery (no central master)
message_filters works in both, but API differs
Custom messages: same .msg format, different build system
Nodelets → ROS2 Components (intra-process communication)
dynamic_reconfigure → ROS2 parameters with callbacks

Start migration from leaf nodes (sensors, actuators) and work inward. Use the ros1_bridge package to run both stacks simultaneously during transition.

ros1-development