Setting navigation goals in ROS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a navigation goal message.

ROS

goal.target_pose.header.frame_id = [1]

Drag options to blanks, or click blank then click option'

A"odom"

B"base_link"

C"camera"

D"map"

Attempts:

3 left

💡 Hint

Common Mistakes

Using robot's base frame instead of map frame

Forgetting quotes around frame_id

The navigation goal frame is usually set to "map" to specify the global coordinate frame.

2fill in blank

medium

Complete the code to set the position x coordinate of the goal.

ROS

goal.target_pose.pose.position.x = [1]

Drag options to blanks, or click blank then click option'

A0

Bgoal_x

C1.0

Dpose_x

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names not defined

Using integers without decimal for floats

The position x coordinate is set to a float value like 1.0 to specify the goal location.

3fill in blank

hard

Fix the error in setting the orientation w component of the goal.

ROS

goal.target_pose.pose.orientation.w = [1]

Drag options to blanks, or click blank then click option'

A1.0

B"1"

C90

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using integer zero instead of float

Using string instead of number

The orientation w component must be a float value like 1.0, not an integer zero or string.

4fill in blank

hard

Fill both blanks to set the goal's orientation as a quaternion with no rotation.

ROS

goal.target_pose.pose.orientation.x = [1]
goal.target_pose.pose.orientation.y = [2]

Drag options to blanks, or click blank then click option'

A0.0

B1.0

C0

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using integer zero without decimal

Using None or null values

For no rotation, quaternion x and y components are set to 0.0.

5fill in blank

hard

Fill all three blanks to set the goal's orientation quaternion correctly for no rotation.

ROS

goal.target_pose.pose.orientation.x = [1]
goal.target_pose.pose.orientation.y = [2]
goal.target_pose.pose.orientation.z = [3]

Drag options to blanks, or click blank then click option'

A0.0

B1.0

C0

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using None for quaternion components

Mixing string and numeric types

For no rotation, quaternion x, y, and z components are zero (x=0.0, y=0.0, z=0). The w component is 1.0 (set elsewhere).

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