Setting navigation goals in ROS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a navigation goal in ROS?

A navigation goal in ROS is a target position and orientation that a robot should reach within its environment using the navigation stack.

beginner

Which ROS message type is commonly used to set a navigation goal?

The geometry_msgs/PoseStamped message is commonly used to specify the position and orientation for a navigation goal.

intermediate

How do you send a navigation goal to the move_base action server?

You create a MoveBaseGoal message with the desired pose and send it to the move_base action server using an action client.

intermediate

Why is the frame_id important when setting a navigation goal?

The frame_id defines the coordinate frame (like 'map' or 'odom') in which the goal position is specified, ensuring the robot interprets the goal correctly.

intermediate

What happens if the robot cannot reach the navigation goal?

The navigation stack will report a failure status, and the robot may try to replan or stop depending on the configuration and recovery behaviors.

Which ROS package is primarily responsible for handling navigation goals?

A rosbag

B tf2

C rviz

D move_base

The move_base package handles navigation goals by planning and controlling the robot to reach the target.

What message type do you use to specify the robot's goal pose?

A geometry_msgs/PoseStamped

B std_msgs/String

C sensor_msgs/Image

D nav_msgs/Path

geometry_msgs/PoseStamped includes position and orientation with a timestamp and frame, perfect for navigation goals.

What is the role of the 'frame_id' in a navigation goal message?

A Defines the robot's battery level

B Specifies the coordinate frame for the goal

C Sets the robot's speed

D Indicates the sensor type

frame_id tells the system which coordinate frame the goal position is relative to, like 'map' or 'odom'.

How does the robot know when it has reached the navigation goal?

A When the robot stops moving

B When the battery is full

C When the move_base action server reports success

D When the sensors detect an obstacle

The move_base action server sends a success status when the robot reaches the goal within a tolerance.

What should you do if the robot fails to reach a navigation goal?

A Check for obstacles and try recovery behaviors

B Ignore the failure and send a new goal immediately

C Turn off the robot

D Change the robot's color

Recovery behaviors help the robot handle obstacles or errors to try reaching the goal again.

Explain how to set a navigation goal in ROS using the move_base action server.

Think about the message type and the action client process.

Describe why coordinate frames matter when setting navigation goals in ROS.

Consider how the robot understands where to go.

Practice

1. What is the main purpose of setting a navigation goal in ROS?

easy

A. To tell the robot where to move using coordinates and orientation

B. To change the robot's color

C. To update the robot's software version

D. To stop the robot immediately

Solution

1. Step 1: Understand navigation goals

   Navigation goals specify a target position and orientation for the robot to reach.

2. Step 2: Identify the purpose

   Setting a navigation goal directs the robot where to move in its environment.

3. Final Answer:

   To tell the robot where to move using coordinates and orientation -> Option A

4. Quick Check:

   Navigation goal = target position [OK]

Hint: Navigation goals set robot's target position and direction [OK]

Common Mistakes:

• Confusing navigation goals with software updates
• Thinking navigation goals change robot appearance
• Assuming navigation goals stop the robot

2. Which ROS frame is commonly used to set navigation goals relative to the environment?

easy

A. "base_link" frame

B. "odom" frame

C. "map" frame

D. "camera" frame

Solution

1. Step 1: Identify common frames in ROS navigation

   Frames like "base_link", "odom", and "map" represent different coordinate systems.

2. Step 2: Choose the frame for environment-relative goals

   The "map" frame is fixed to the environment and used for global navigation goals.

3. Final Answer:

   "map" frame -> Option C

4. Quick Check:

   Environment-relative goals use "map" frame [OK]

Hint: "map" frame is fixed to environment, perfect for goals [OK]

Common Mistakes:

• Using "base_link" which is robot-centered
• Choosing "odom" which drifts over time
• Selecting "camera" which is unrelated to navigation

3. Given this ROS Python snippet to send a navigation goal:

goal.target_pose.header.frame_id = "map"
goal.target_pose.pose.position.x = 2.0
goal.target_pose.pose.position.y = 3.0
goal.target_pose.pose.orientation.w = 1.0
client.send_goal(goal)
client.wait_for_result()

What will the robot do?

medium

A. Throw an error due to missing orientation x, y, z

B. Move to position (3.0, 2.0) on the map facing backward

C. Stay still because orientation is incomplete

D. Move to position (2.0, 3.0) on the map facing forward

Solution

1. Step 1: Analyze position and orientation values

   Position is set to x=2.0, y=3.0; orientation.w=1.0 means no rotation (facing forward).

2. Step 2: Understand client commands

   Sending goal and waiting for result commands the robot to move to the specified pose.

3. Final Answer:

   Move to position (2.0, 3.0) on the map facing forward -> Option D

4. Quick Check:

   Goal pose = (2.0,3.0), orientation forward [OK]

Hint: Orientation w=1 means facing forward, position sets location [OK]

Common Mistakes:

• Mixing up x and y coordinates
• Assuming missing orientation x,y,z causes error
• Thinking orientation.w=1 means backward

4. What is wrong with this ROS Python code snippet for setting a navigation goal?

goal.target_pose.header.frame_id = "map"
goal.target_pose.pose.position.x = 1.0
goal.target_pose.pose.position.y = 2.0
client.send_goal(goal)
client.wait_for_result()

medium

A. frame_id should be "odom" instead of "map"

B. Missing orientation in goal.pose causes navigation failure

C. Position values must be integers, not floats

D. client.wait_for_result() must come before send_goal()

Solution

1. Step 1: Check completeness of goal pose

   Orientation is not set, which is required for a valid navigation goal.

2. Step 2: Verify other parts

   frame_id "map" is correct; position floats are allowed; wait_for_result() must follow send_goal().

3. Final Answer:

   Missing orientation in goal.pose causes navigation failure -> Option B

4. Quick Check:

   Orientation required for goal [OK]

Hint: Always set orientation when sending navigation goals [OK]

Common Mistakes:

• Ignoring missing orientation
• Changing frame_id unnecessarily
• Misordering wait_for_result and send_goal

5. You want the robot to navigate to two different points sequentially using ROS move_base. Which approach correctly sets and sends these goals?

hard

A. Send first goal, wait for result, then send second goal and wait again

B. Send both goals at the same time without waiting

C. Send second goal first, then send first goal after completion

D. Only send the last goal; the robot will visit both automatically

Solution

1. Step 1: Understand sequential goal sending

   To visit points in order, send one goal and wait for it to finish before sending the next.

2. Step 2: Evaluate options

   Sending both simultaneously confuses the robot; sending second first breaks order; last goal alone ignores first.

3. Final Answer:

   Send first goal, wait for result, then send second goal and wait again -> Option A

4. Quick Check:

   Sequential goals need wait between sends [OK]

Hint: Wait for each goal to finish before sending next [OK]

Common Mistakes:

• Sending multiple goals simultaneously
• Assuming robot queues goals automatically
• Sending goals in wrong order