rosparam command-line tools - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the rosparam command-line tool in ROS?

The rosparam tool is used to get, set, load, and delete parameters on the ROS parameter server from the command line. It helps manage configuration data for ROS nodes.

beginner

How do you load parameters from a YAML file into the ROS parameter server using rosparam?

Use rosparam load <file.yaml> [namespace] to load parameters from a YAML file into the parameter server optionally under a namespace.

beginner

What command would you use to delete a parameter named /robot_speed from the parameter server?

Use rosparam delete /robot_speed to remove the parameter /robot_speed from the parameter server.

intermediate

Explain the difference between rosparam get and rosparam dump.

rosparam get <param_name> retrieves the value of a single parameter. rosparam dump <file.yaml> [namespace] saves all parameters or those under a namespace to a YAML file.

beginner

How can you set a parameter named /max_speed to 5.0 using rosparam?

Use rosparam set /max_speed 5.0 to set the parameter /max_speed to the value 5.0 on the parameter server.

Which rosparam command loads parameters from a YAML file?

A rosparam set file.yaml

B rosparam get file.yaml

C rosparam load file.yaml

D rosparam delete file.yaml

rosparam load loads parameters from a YAML file into the parameter server.

How do you retrieve the value of a parameter named /robot_name?

A rosparam get /robot_name

B rosparam set /robot_name

C rosparam load /robot_name

D rosparam delete /robot_name

rosparam get /robot_name fetches the value of the parameter from the server.

What does rosparam dump params.yaml do?

A Saves all parameters to params.yaml

B Loads parameters from params.yaml

C Deletes parameters listed in params.yaml

D Sets parameters to default values

rosparam dump saves parameters from the server to a YAML file.

Which command deletes a parameter named /speed_limit?

A rosparam get /speed_limit

B rosparam delete /speed_limit

C rosparam set /speed_limit

D rosparam load /speed_limit

rosparam delete removes a parameter from the server.

If you want to set a parameter /threshold to 10, which command do you use?

A rosparam get /threshold 10

B rosparam delete /threshold 10

C rosparam load /threshold 10

D rosparam set /threshold 10

rosparam set assigns a value to a parameter.

Describe how you would use rosparam to manage parameters for a ROS node, including loading, setting, getting, and deleting parameters.

Think about how you handle configuration files and changing settings in a program.

Explain the difference between rosparam get and rosparam dump and when you might use each.

One is for reading one value, the other is for saving many values.

Practice

1. What is the primary purpose of the rosparam command-line tool in ROS?

easy

A. To compile ROS packages

B. To visualize robot models

C. To launch ROS nodes

D. To manage parameters on the ROS parameter server

Solution

1. Step 1: Understand the role of rosparam

   rosparam is designed to interact with the ROS parameter server, allowing users to set, get, and delete parameters.

2. Step 2: Differentiate from other ROS tools

   Compiling packages is done by catkin_make, launching nodes by roslaunch, and visualization by tools like rviz. These are unrelated to parameter management.

3. Final Answer:

   To manage parameters on the ROS parameter server -> Option D

4. Quick Check:

   rosparam manages parameters = B [OK]

Hint: rosparam always deals with parameters, not nodes or builds [OK]

Common Mistakes:

• Confusing rosparam with roslaunch
• Thinking rosparam compiles code
• Assuming rosparam visualizes data

2. Which of the following is the correct syntax to set a parameter named robot_speed to 1.5 using rosparam?

easy

A. rosparam get robot_speed 1.5

B. rosparam set robot_speed 1.5

C. rosparam load robot_speed 1.5

D. rosparam delete robot_speed 1.5

Solution

1. Step 1: Identify the command to assign a value

   The set command is used to assign a value to a parameter on the ROS parameter server.

2. Step 2: Check the syntax format

   The correct syntax is rosparam set <param_name> <value>. So rosparam set robot_speed 1.5 is correct.

3. Final Answer:

   rosparam set robot_speed 1.5 -> Option B

4. Quick Check:

   Set command assigns value = A [OK]

Hint: Use 'set' to assign values, not 'get' or 'load' [OK]

Common Mistakes:

• Using 'get' to set a value
• Confusing 'load' with 'set'
• Adding extra arguments after parameter name

3. Given the following commands run in order:

rosparam set /max_speed 2.0
rosparam get /max_speed
rosparam delete /max_speed
rosparam get /max_speed

What will be the output of the second rosparam get /max_speed command?

medium

A. Parameter /max_speed not set

B. 0

C. 2.0

D. Error: invalid command

Solution

1. Step 1: Understand the sequence of commands

   First, the parameter /max_speed is set to 2.0. Then it is retrieved, so the first get returns 2.0. Next, the parameter is deleted.

2. Step 2: Check the second get command after deletion

   After deletion, the parameter no longer exists on the server. So the second get command will report that the parameter is not set.

3. Final Answer:

   Parameter /max_speed not set -> Option A

4. Quick Check:

   Deleted parameter returns 'not set' = C [OK]

Hint: Deleted parameters return 'not set' on get [OK]

Common Mistakes:

• Assuming deleted parameters return default 0
• Expecting an error instead of a message
• Confusing set and delete effects

4. You run the command rosparam load config.yaml but get an error saying the file does not exist. What is the most likely cause?

medium

A. The YAML file path is incorrect or file is missing

B. rosparam cannot load YAML files

C. You need to use rosparam set instead of load

D. The parameter server is not running

Solution

1. Step 1: Understand rosparam load requirements

   The rosparam load command requires a valid YAML file path to load parameters from.

2. Step 2: Identify common causes of file errors

   If the file does not exist or the path is wrong, rosparam will report an error. The parameter server must be running, but that usually causes a different error.

3. Final Answer:

   The YAML file path is incorrect or file is missing -> Option A

4. Quick Check:

   File missing causes load error = A [OK]

Hint: Check file path carefully before loading YAML [OK]

Common Mistakes:

• Thinking rosparam can't load YAML files
• Using set instead of load for files
• Ignoring parameter server status

5. You want to save all current parameters under the namespace /robot to a file named robot_params.yaml. Which command correctly does this?

hard

A. rosparam get /robot > robot_params.yaml

B. rosparam load robot_params.yaml /robot

C. rosparam dump robot_params.yaml /robot

D. rosparam set /robot robot_params.yaml

Solution

1. Step 1: Identify the command to save parameters

   rosparam dump saves parameters to a YAML file. It takes the filename and optionally a namespace.

2. Step 2: Match the syntax to the requirement

   To save parameters under /robot to robot_params.yaml, the command is rosparam dump robot_params.yaml /robot.

3. Final Answer:

   rosparam dump robot_params.yaml /robot -> Option C

4. Quick Check:

   Dump saves parameters to file = D [OK]

Hint: Use 'dump' to save parameters, 'load' to restore [OK]

Common Mistakes:

• Using load instead of dump to save
• Trying to redirect get output to file
• Confusing set with dump