Map saving and loading in ROS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to save a map using the ROS map_server node.

ROS

rosrun map_server map_saver -f [1]

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

Amap_file

Bload_map

Cmy_map

Dsave_map

Attempts:

3 left

💡 Hint

Common Mistakes

Using a command other than map_saver to save the map.

Providing a filename with spaces or invalid characters.

The map_saver node saves the map to a file with the given name. Here, my_map is the filename prefix.

2fill in blank

medium

Complete the command to load a saved map using the ROS map_server node.

ROS

rosrun map_server map_server [1].yaml

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

Amy_map

Bmap_save

Cmap_load

Dload_map

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong filename or extension.

Confusing map_saver with map_server.

The map_server node loads a map from a YAML file. The filename should match the saved map prefix.

3fill in blank

hard

Fix the error in the command to save a map with a custom filename.

ROS

rosrun map_server [1] -f custom_map

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

Amap_saver

Bmap_server

Cmap_loader

Dmap_save

Attempts:

3 left

💡 Hint

Common Mistakes

Using map_server instead of map_saver to save maps.

Using non-existent node names like map_loader.

The map_saver node is used to save maps. Using map_server here is incorrect because it loads maps.

4fill in blank

hard

Fill both blanks to correctly save a map with a specific filename and format.

ROS

rosrun map_server [1] -f [2]

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

Amap_saver

Bmap_server

Ccustom_map

Ddefault_map

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the node name and filename.

Using map_server to save maps.

Use map_saver to save the map and specify the filename prefix as custom_map.

5fill in blank

hard

Fill all three blanks to load a map and start the ROS node with a specific namespace and map file.

ROS

roslaunch map_server map_server.launch map_file:=[1] namespace:=[2] [3]

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

Amy_map.yaml

Brobot1

C__ns:=robot1

Dmap.yaml

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect file extensions.

Confusing namespace parameter with remapping syntax.

The map_file parameter specifies the YAML map file. The namespace sets the ROS namespace. The __ns:=robot1 remaps the namespace for the node.

Practice

1. What is the primary purpose of using map_saver in ROS?

easy

A. To control the robot's movement based on the map

B. To load a previously saved map into the robot's system

C. To save the current map of the robot's environment to files

D. To visualize the robot's sensor data in real-time

Solution

1. Step 1: Understand the role of map_saver

   map_saver is a ROS tool used to save the map data the robot has explored.

2. Step 2: Differentiate from map_server

   map_server is used to load maps, not save them.

3. Final Answer:

   To save the current map of the robot's environment to files -> Option C

4. Quick Check:

   Saving maps = map_saver [OK]

Hint: Remember: saver saves, server loads maps [OK]

Common Mistakes:

• Confusing map_saver with map_server
• Thinking map_saver controls robot movement
• Assuming map_saver visualizes sensor data

2. Which command correctly saves a map in ROS using map_saver?

easy

A. rosrun map_saver map_server -f my_map

B. rosrun map_saver save_map -o my_map

C. roslaunch map_saver save_map.launch

D. rosrun map_server map_saver -f my_map

Solution

1. Step 1: Recall the correct command syntax

   The correct command to save a map is rosrun map_server map_saver -f filename.

2. Step 2: Check each option

   rosrun map_server map_saver -f my_map matches the correct syntax. The other options have incorrect package names, flags, or commands.

3. Final Answer:

   rosrun map_server map_saver -f my_map -> Option D

4. Quick Check:

   Correct save command = rosrun map_server map_saver -f my_map [OK]

Hint: Use rosrun map_server map_saver -f filename to save [OK]

Common Mistakes:

• Swapping map_saver and map_server in command
• Using wrong flags like -o instead of -f
• Using roslaunch instead of rosrun for map_saver

3. Given the following command:

rosrun map_server map_saver -f office_map

What files will be created after running this command?

medium

A. office_map.pgm and office_map.yaml

B. office_map.txt and office_map.yaml

C. office_map.png and office_map.json

D. office_map.map and office_map.config

Solution

1. Step 1: Understand map_saver output files

   map_saver saves maps as an image file (.pgm) and a YAML file (.yaml) describing the map metadata.

2. Step 2: Match file extensions to options

   office_map.pgm and office_map.yaml correctly lists .pgm and .yaml files. Other options list incorrect file types.

3. Final Answer:

   office_map.pgm and office_map.yaml -> Option A

4. Quick Check:

   Map files = .pgm + .yaml [OK]

Hint: Map saves as .pgm image and .yaml metadata files [OK]

Common Mistakes:

• Expecting .png or .json files instead of .pgm and .yaml
• Confusing .txt or .map extensions with map files
• Thinking map_saver creates only one file

4. You try to load a saved map using rosrun map_server map_server office_map.yaml but get an error saying the map file is missing. What is the most likely cause?

medium

A. The map_server command requires a .pgm file, not a YAML file

B. The .pgm image file is missing or not in the same folder as the YAML file

C. The YAML file is corrupted and cannot be read

D. The robot's sensors are not turned on

Solution

1. Step 1: Understand map_server loading requirements

   map_server loads the YAML file which references the .pgm image file. Both must be present in the same folder.

2. Step 2: Analyze the error cause

   If the .pgm file is missing, map_server cannot load the map, causing the error.

3. Final Answer:

   The .pgm image file is missing or not in the same folder as the YAML file -> Option B

4. Quick Check:

   Missing .pgm file causes load error [OK]

Hint: YAML needs matching .pgm file in same folder to load [OK]

Common Mistakes:

• Trying to load only the .pgm file without YAML
• Assuming sensors affect map_server loading
• Confusing file corruption with missing files

5. You want to save a map and then load it later for robot navigation. Which sequence of commands correctly achieves this?

hard

A. rosrun map_server map_saver -f home_maprosrun map_server map_server home_map.yaml

B. rosrun map_saver map_server -f home_maprosrun map_server map_saver home_map.yaml

C. roslaunch map_saver save.launch -map home_maproslaunch map_server load.launch -map home_map

D. rosrun map_server map_server -f home_maprosrun map_server map_saver home_map.yaml

Solution

1. Step 1: Save the map using map_saver

   Use rosrun map_server map_saver -f home_map to save the map files.

2. Step 2: Load the saved map using map_server

   Use rosrun map_server map_server home_map.yaml to load the saved map for navigation.

3. Step 3: Verify command correctness

   rosrun map_server map_saver -f home_map
rosrun map_server map_server home_map.yaml correctly shows the save then load sequence. Other options mix commands or use incorrect syntax.

4. Final Answer:

   rosrun map_server map_saver -f home_map then rosrun map_server map_server home_map.yaml -> Option A

5. Quick Check:

   Save then load with map_saver and map_server [OK]

Hint: Save first with map_saver, then load with map_server [OK]

Common Mistakes:

• Mixing up map_saver and map_server commands
• Using roslaunch instead of rosrun incorrectly
• Trying to load before saving the map