===== P1 - Mobile Robot Exploration ======
The main task is to implement ROS modules based on the tasks: [[courses:b4m36uir:hw:t1a-ctrl|T1a-ctrl]], [[courses:b4m36uir:hw:t1c-map|T1c-map]], [[courses:b4m36uir:hw:t1d-plan|T1d-plan]], and [[courses:b4m36uir:hw:t1e-expl|T1e-expl]] and thus create an integrated solution for autonomous robotic exploration.
|**Deadline** | January 5th, 23:59 PST |
|**Points** | 15 |
|**Label in BRUTE** | P1 |
|**Evaluation** | Solution is evaluated by a demonstration to an instructor |
|**Resources** | {{:courses:b4m36uir:hw:uir-p1-expl.zip | P1-expl resource package}} |
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===Assignment===
Implement ROS nodes to solve the exploration tasks.
The provided resource pack support deployment using both the V-REP and STDR simulators.
Moreover, an R-VIZ setup file is provided to visualize the robot knowledge of the environment using the messages published by the individual ROS nodes.
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==Simulators==
The simulators provide and process the following inputs and outputs, respectively
| | Message type | ROS Topic | Description |
| Outputs | Laser scan ([[http://docs.ros.org/melodic/api/sensor_msgs/html/msg/LaserScan.html|sensor_msgs/LaserScan]]) | /robot0/laser_0 | Range measurements from a sensor |
| | Robot pose ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/Odometry.html|nav_msgs/Odometry]]) | /robot0/odom | Robot pose provided by a simulator |
| Inputs | Velocity command ([[https://docs.ros.org/api/geometry_msgs/html/msg/Twist.html|geometry_msgs/Twist]] ) | /robot0/cmd_vel | Velocities to drive the robot |
To run the V-REP simulator
- run V-REP
- open a scene, e.g., ''blocks.ttt''
- launch the ROS node
roslaunch uir_tools uir_backend_vrep.launch
When running the V-REP simulator, calling ''rospy.Time.now()'' causes the V-REP simulation time to freeze.
Therefore, when using V-REP subscribe to the ROS topic ''/clock'' to get the current ROS time.
To run the STDR simulator
- launch the ROS node
roslaunch uir_tools uir_backend_stdr.launch
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==RVIZ==
The provided RVIZ setup file may be used to visualize the following topics
| Message type | Topic | Description |
| Robot odometry ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/Odometry.html|nav_msgs/Odometry]]) | /robot0/odom | Robot position and orientation provided by a simulator |
| Laser scans ([[http://docs.ros.org/melodic/api/sensor_msgs/html/msg/LaserScan.html|sensor_msgs/LaserScan]]) | /robot0/laser_0 | Range measurements from a sensor |
| Path ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/Path.html|nav_msgs/Path]]) | /robot0/path | Path to be followed by the robot |
| Occupancy map ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/OccupancyGrid.html|nav_msgs/OccupancyGrid]] ) | /gridmap | Map of the robot surroundings |
| Point cloud ([[http://docs.ros.org/melodic/api/sensor_msgs/html/msg/PointCloud2.html|sensor_msgs/PointCloud2]] ) | /frontiers/cells | Frontier cells detected by the robot |
| Point cloud ([[http://docs.ros.org/melodic/api/sensor_msgs/html/msg/PointCloud2.html|sensor_msgs/PointCloud2]] ) | /frontiers/clusters | Clustered frontier cells |
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== Expected Behavior ==
{{:courses:b4m36uir:projects:p1.gif?300|}}
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=== Evaluation ===
A demonstration of the working robotic exploration in STDR or V-REP simulator is evaluated by an instructor during the labs.
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===Suggested architecture===
The individual nodes roughly correspond to [[courses:b4m36uir:hw:t1a-ctrl|T1a-ctrl]], [[courses:b4m36uir:hw:t1c-map|T1c-map]], and [[courses:b4m36uir:hw:t1d-plan|T1d-plan]] paired with [[courses:b4m36uir:hw:t1e-expl|T1e-expl]].
The following text describes the recommended architecture of ROS modules, and extends the idea of robotic exploration.
Note, it is strongly recommended to first prepare the ROS interface and test whether the messages are correctly sent and received.
Then, connect all the interfaces within the ROS framework and test all the modules together.
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==Path following module==
The path following module drives the robot along a given path by publishing velocity commands.
| | Message type | Topic | Description
| Inputs | Path ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/Path.html|nav_msgs/Path]]) | /robot0/path | Path to be followed by the robot |
| | Robot odometry ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/Odometry.html|nav_msgs/Odometry]]) | /robot0/odom | Robot position and orientation provided by a simulator |
| Outputs | Velocity command ([[https://docs.ros.org/api/geometry_msgs/html/msg/Twist.html|geometry_msgs/Twist]] ) | /robot0/cmd_vel | Velocities to drive the robot |
Unlike in [[courses:b4m36uir:hw:t1a-ctrl|T1a-ctrl]], where the left and right velocity is used control the robot, the simulators accept [[https://docs.ros.org/api/geometry_msgs/html/msg/Twist.html|geometry_msgs/Twist]]. Therefore, for your convenience a simplistic path follower is already prepared in the resource pack's ''uir_path_follower'' node.
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===Mapping module===
The mapping module incrementally builds a map of the robot surroundings from the robot sensoric measurements.
| | Message type | Topic | Description
| Inputs | Laser scans ([[http://docs.ros.org/melodic/api/sensor_msgs/html/msg/LaserScan.html|sensor_msgs/LaserScan]]) | /robot0/laser_0 | Range measurements from a sensor |
| | Robot pose ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/Odometry.html|nav_msgs/Odometry]]) | /robot0/odom | Robot pose provided by a simulator |
| Outputs | Occupancy map ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/OccupancyGrid.html|nav_msgs/OccupancyGrid]] ) | /gridmap | Map of the robot surroundings |
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===Exploration module===
The exploration module selects the exploration goals and plans paths for the robot to explore.
| | Message type | Topic | Description
| Inputs | Occupancy map ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/OccupancyGrid.html|nav_msgs/OccupancyGrid]] ) | /gridmap |Map of the robot surroundings |
| | Robot pose ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/Odometry.html|nav_msgs/Odometry]]) | /robot0/odom | Robot pose provided by a simulator |
| Outputs | Point cloud ([[http://docs.ros.org/melodic/api/sensor_msgs/html/msg/PointCloud2.html|sensor_msgs/PointCloud2]] ) | /frontiers/cells | Frontier cells detected by the robot (for visualization only) |
| | Point cloud ([[http://docs.ros.org/melodic/api/sensor_msgs/html/msg/PointCloud2.html|sensor_msgs/PointCloud2]] ) | /frontiers/clusters | Clustered frontier cells (for visualization only) |
| | Path ([[http://docs.ros.org/melodic/api/nav_msgs/html/msg/Path.html|nav_msgs/Path]]) | /robot0/path | Path followed by the robot |
This node is based on the tasks [[courses:b4m36uir:hw:t1d-plan|T1d-plan]] and [[courses:b4m36uir:hw:t1e-expl|T1e-expl]].
In the frontier based approach, the path is to be planned to the closest location selected among the detected frontiers, i.e., the borders between the free and unknown space.
Note, it is beneficial to cluster the observed frontiers cells to reduce the computational load of goal selection.
Moreover, keep in mind that even in a simulator the path is not executed perfectly.
Therefore, using a safety margin around the walls is advisable.
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===Appendix===
==Setup==
To run the ROS nodes, it is strongly recommended to use either Ubuntu 16 with ROS Kinetic or Ubuntu 18 with ROS Melodic.
Detailed installation instructions may be found on ROS web pages
[[http://wiki.ros.org/kinetic/Installation/Ubuntu|ROS Kinetic]], [[http://wiki.ros.org/melodic/Installation/Ubuntu|ROS Melodic]].
On the lab computers, ROS Kinetic is already preinstalled but two more libraries need to be installed before using it.
pip install rospkg
pip install netifaces
Moreover, it is necessary to source the main ROS setup script, which has to be done in each new terminal instance.
Thus, it is recommended to add the following source command in your ''~/.bashrc'' file
echo "source /opt/ros/kinetic/setup.bash" >> ~/.bashrc
or alternatively when running ROS Meloding
echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc
Finally, on Ubuntu 16 the STDR simulator is installed using
sudo apt-get install ros-kinetic-stdr-*
On Ubuntu 18, STDR has to be compiled from source, which can be found at [[https://github.com/stdr-simulator-ros-pkg/stdr_simulator]].
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==ROS Basics==
On Ubuntu 16 and 18 the ROS workspace is created as follows
cd ~/
mkdir rds_ws
mkdir rds_ws/src
cd rds_ws
catkin_make
# source the workspace
cd devel
devel_path=$(pwd)
echo "source $devel_path/setup.bash" >> ~/.bashrc
source setup.bash
# Add new (custom) package to the workspace
cd ~/rds_ws/src # Go to src folder in your workspace.
ln -s [path to your package] # Create symlink to your package (or place the whole package directly to src).
cd ~/rds_ws
catkin_make # Compile the workspace.
rospack list # Make sure that your pack is known. (Sometimes this is necessary to refresh ROS. )
# Now, you should be able to use the package within ROS (rosrun or roslaunch).
# useful commands
rostopic list # all current topics in the ROS system
rostopic info [topic name] # show info about topic - publishers, subscribers
rostopic echo [topic name] # writes msgs data on certain topic to stdout
rostopic hz [topic name] # prints frequency of msgs on a certain topic
rosnode list # all currently running nodes
rosnode info [node name] # info about the node: published topics, subscribed topics
# useful tools
rqt_graph # visualize connection between the nodes (might not be 100% accurate)
rviz # spatial visualization of the msgs
rosrun tf view_frames # creates pdf with a visualization of the whole transformation tree (all the /tf msgs in the system)
rosbag record # capture ROS msgs on selected topics (data can be played with selected speed afterwards)
rosbag play [bagfile] # play data saved in bagfile
The main study material for ROS is [[http://wiki.ros.org/ROS/Tutorials]].
A special attention should be given to ROS message-based communication presented in [[http://wiki.ros.org/ROS/Tutorials/WritingPublisherSubscriber%28python%29]].