Create Custom Messages from ROS 2 Package

Use custom messages to extend the set of message types currently supported in ROS 2. Custom messages are messages that you define. If you are sending and receiving supported message types, you do not need to use custom messages. To see a list of supported message types, enter ros2 msg list in the MATLAB® Command Window. For more information about supported ROS 2 messages, see Work with Basic ROS 2 Messages.

If this if your first time working with ROS 2 custom messages, see ROS Toolbox System Requirements.

ROS 2 custom messages are specified in ROS 2 package folders that contain a folder named msg. The msg folder contains all your custom message type definitions. For example, the example_b_msgs package in the custom folder, has this folder and file structure.

The package contains the custom message type Standalone.msg. MATLAB uses these files to generate the necessary files for using the custom messages contained in the package.

In this example, you create ROS 2 custom messages in MATLAB. You must have a ROS 2 package that contains the required msg file.

After ensuring that your custom message package is correct, you specify the path to the parent folder and call ros2genmsg with the specified path. The following example provided three messages example_package_a, example_package_b, and example_package_c that have dependencies. This example also illustrates that you can use a folder containing multiple messages and generate them all at the same time.

Open a new MATLAB session and create a custom message folder in a local folder.

folderPath = fullfile(pwd,"custom");
copyfile("example_*_msgs",folderPath);

Specify the folder path for custom message files and use ros2genmsg to create custom messages.

ros2genmsg(folderPath)

Identifying message files in folder 'C:/Work/custom'.Done.
Removing previous version of Python virtual environment.Done.
Creating a Python virtual environment.Done.
Adding required Python packages to virtual environment.Done.
Copying include folders.Done.
Copying libraries.Done.
Validating message files in folder 'C:/Work/custom'.Done.
[3/3] Generating MATLAB interfaces for custom message packages... Done.
Running colcon build in folder 'C:/Work/custom/matlab_msg_gen/win64'.
Build in progress. This may take several minutes...
Build succeeded.build log

Call ros2 msg list to verify creation of new custom messages.

ros2 msg list

action_msgs/CancelGoalRequest
action_msgs/CancelGoalResponse
action_msgs/GoalInfo
action_msgs/GoalStatus
action_msgs/GoalStatusArray
actionlib_msgs/GoalID
actionlib_msgs/GoalStatus
actionlib_msgs/GoalStatusArray
builtin_interfaces/Duration
builtin_interfaces/Time
composition_interfaces/ListNodesRequest
composition_interfaces/ListNodesResponse
composition_interfaces/LoadNodeRequest
composition_interfaces/LoadNodeResponse
composition_interfaces/UnloadNodeRequest
composition_interfaces/UnloadNodeResponse
diagnostic_msgs/AddDiagnosticsRequest
diagnostic_msgs/AddDiagnosticsResponse
diagnostic_msgs/DiagnosticArray
diagnostic_msgs/DiagnosticStatus
diagnostic_msgs/KeyValue
diagnostic_msgs/SelfTestRequest
diagnostic_msgs/SelfTestResponse
example_a_msgs/DependsOnB
example_b_msgs/Standalone
example_c_msgs/DependsOnB
example_interfaces/AddTwoIntsRequest
example_interfaces/AddTwoIntsResponse
example_interfaces/Bool
example_interfaces/Byte
example_interfaces/ByteMultiArray
example_interfaces/Char
example_interfaces/Empty
example_interfaces/Float32
example_interfaces/Float32MultiArray
example_interfaces/Float64
example_interfaces/Float64MultiArray
example_interfaces/Int16
example_interfaces/Int16MultiArray
example_interfaces/Int32
example_interfaces/Int32MultiArray
example_interfaces/Int64
example_interfaces/Int64MultiArray
example_interfaces/Int8
example_interfaces/Int8MultiArray
example_interfaces/MultiArrayDimension
example_interfaces/MultiArrayLayout
example_interfaces/SetBoolRequest
example_interfaces/SetBoolResponse
example_interfaces/String
example_interfaces/TriggerRequest
example_interfaces/TriggerResponse
example_interfaces/UInt16
example_interfaces/UInt16MultiArray
example_interfaces/UInt32
example_interfaces/UInt32MultiArray
example_interfaces/UInt64
example_interfaces/UInt64MultiArray
example_interfaces/UInt8
example_interfaces/UInt8MultiArray
example_interfaces/WString
geometry_msgs/Accel
geometry_msgs/AccelStamped
geometry_msgs/AccelWithCovariance
geometry_msgs/AccelWithCovarianceStamped
geometry_msgs/Inertia
geometry_msgs/InertiaStamped
geometry_msgs/Point
geometry_msgs/Point32
geometry_msgs/PointStamped
geometry_msgs/Polygon
geometry_msgs/PolygonStamped
geometry_msgs/Pose
geometry_msgs/Pose2D
geometry_msgs/PoseArray
geometry_msgs/PoseStamped
geometry_msgs/PoseWithCovariance
geometry_msgs/PoseWithCovarianceStamped
geometry_msgs/Quaternion
geometry_msgs/QuaternionStamped
geometry_msgs/Transform
geometry_msgs/TransformStamped
geometry_msgs/Twist
geometry_msgs/TwistStamped
geometry_msgs/TwistWithCovariance
geometry_msgs/TwistWithCovarianceStamped
geometry_msgs/Vector3
geometry_msgs/Vector3Stamped
geometry_msgs/Wrench
geometry_msgs/WrenchStamped
lifecycle_msgs/ChangeStateRequest
lifecycle_msgs/ChangeStateResponse
lifecycle_msgs/GetAvailableStatesRequest
lifecycle_msgs/GetAvailableStatesResponse
lifecycle_msgs/GetAvailableTransitionsRequest
lifecycle_msgs/GetAvailableTransitionsResponse
lifecycle_msgs/GetStateRequest
lifecycle_msgs/GetStateResponse
lifecycle_msgs/State
lifecycle_msgs/Transition
lifecycle_msgs/TransitionDescription
lifecycle_msgs/TransitionEvent
logging_demo/ConfigLoggerRequest
logging_demo/ConfigLoggerResponse
map_msgs/GetMapROIRequest
map_msgs/GetMapROIResponse
map_msgs/GetPointMapROIRequest
map_msgs/GetPointMapROIResponse
map_msgs/GetPointMapRequest
map_msgs/GetPointMapResponse
map_msgs/OccupancyGridUpdate
map_msgs/PointCloud2Update
map_msgs/ProjectedMap
map_msgs/ProjectedMapInfo
map_msgs/ProjectedMapsInfoRequest
map_msgs/ProjectedMapsInfoResponse
map_msgs/SaveMapRequest
map_msgs/SaveMapResponse
map_msgs/SetMapProjectionsRequest
map_msgs/SetMapProjectionsResponse
nav_msgs/GetMapRequest
nav_msgs/GetMapResponse
nav_msgs/GetPlanRequest
nav_msgs/GetPlanResponse
nav_msgs/GridCells
nav_msgs/MapMetaData
nav_msgs/OccupancyGrid
nav_msgs/Odometry
nav_msgs/Path
nav_msgs/SetMapRequest
nav_msgs/SetMapResponse
pendulum_msgs/JointCommand
pendulum_msgs/JointState
pendulum_msgs/RttestResults
rcl_interfaces/DescribeParametersRequest
rcl_interfaces/DescribeParametersResponse
rcl_interfaces/FloatingPointRange
rcl_interfaces/GetParameterTypesRequest
rcl_interfaces/GetParameterTypesResponse
rcl_interfaces/GetParametersRequest
rcl_interfaces/GetParametersResponse
rcl_interfaces/IntegerRange
rcl_interfaces/ListParametersRequest
rcl_interfaces/ListParametersResponse
rcl_interfaces/ListParametersResult
rcl_interfaces/Log
rcl_interfaces/Parameter
rcl_interfaces/ParameterDescriptor
rcl_interfaces/ParameterEvent
rcl_interfaces/ParameterEventDescriptors
rcl_interfaces/ParameterType
rcl_interfaces/ParameterValue
rcl_interfaces/SetParametersAtomicallyRequest
rcl_interfaces/SetParametersAtomicallyResponse
rcl_interfaces/SetParametersRequest
rcl_interfaces/SetParametersResponse
rcl_interfaces/SetParametersResult
rosgraph_msgs/Clock
sensor_msgs/BatteryState
sensor_msgs/CameraInfo
sensor_msgs/ChannelFloat32
sensor_msgs/CompressedImage
sensor_msgs/FluidPressure
sensor_msgs/Illuminance
sensor_msgs/Image
sensor_msgs/Imu
sensor_msgs/JointState
sensor_msgs/Joy
sensor_msgs/JoyFeedback
sensor_msgs/JoyFeedbackArray
sensor_msgs/LaserEcho
sensor_msgs/LaserScan
sensor_msgs/MagneticField
sensor_msgs/MultiDOFJointState
sensor_msgs/MultiEchoLaserScan
sensor_msgs/NavSatFix
sensor_msgs/NavSatStatus
sensor_msgs/PointCloud
sensor_msgs/PointCloud2
sensor_msgs/PointField
sensor_msgs/Range
sensor_msgs/RegionOfInterest
sensor_msgs/RelativeHumidity
sensor_msgs/SetCameraInfoRequest
sensor_msgs/SetCameraInfoResponse
sensor_msgs/Temperature
sensor_msgs/TimeReference
shape_msgs/Mesh
shape_msgs/MeshTriangle
shape_msgs/Plane
shape_msgs/SolidPrimitive
simple_msgs/AddTwoIntsRequest
simple_msgs/AddTwoIntsResponse
simple_msgs/Num
statistics_msgs/MetricsMessage
statistics_msgs/StatisticDataPoint
statistics_msgs/StatisticDataType
std_msgs/Bool
std_msgs/Byte
std_msgs/ByteMultiArray
std_msgs/Char
std_msgs/ColorRGBA
std_msgs/Empty
std_msgs/Float32
std_msgs/Float32MultiArray
std_msgs/Float64
std_msgs/Float64MultiArray
std_msgs/Header
std_msgs/Int16
std_msgs/Int16MultiArray
std_msgs/Int32
std_msgs/Int32MultiArray
std_msgs/Int64
std_msgs/Int64MultiArray
std_msgs/Int8
std_msgs/Int8MultiArray
std_msgs/MultiArrayDimension
std_msgs/MultiArrayLayout
std_msgs/String
std_msgs/UInt16
std_msgs/UInt16MultiArray
std_msgs/UInt32
std_msgs/UInt32MultiArray
std_msgs/UInt64
std_msgs/UInt64MultiArray
std_msgs/UInt8
std_msgs/UInt8MultiArray
std_srvs/EmptyRequest
std_srvs/EmptyResponse
std_srvs/SetBoolRequest
std_srvs/SetBoolResponse
std_srvs/TriggerRequest
std_srvs/TriggerResponse
stereo_msgs/DisparityImage
test_msgs/Arrays
test_msgs/ArraysRequest
test_msgs/ArraysResponse
test_msgs/BasicTypes
test_msgs/BasicTypesRequest
test_msgs/BasicTypesResponse
test_msgs/BoundedSequences
test_msgs/Builtins
test_msgs/Constants
test_msgs/Defaults
test_msgs/Empty
test_msgs/EmptyRequest
test_msgs/EmptyResponse
test_msgs/MultiNested
test_msgs/Nested
test_msgs/Strings
test_msgs/UnboundedSequences
test_msgs/WStrings
trajectory_msgs/JointTrajectory
trajectory_msgs/JointTrajectoryPoint
trajectory_msgs/MultiDOFJointTrajectory
trajectory_msgs/MultiDOFJointTrajectoryPoint
unique_identifier_msgs/UUID
visualization_msgs/GetInteractiveMarkersRequest
visualization_msgs/GetInteractiveMarkersResponse
visualization_msgs/ImageMarker
visualization_msgs/InteractiveMarker
visualization_msgs/InteractiveMarkerControl
visualization_msgs/InteractiveMarkerFeedback
visualization_msgs/InteractiveMarkerInit
visualization_msgs/InteractiveMarkerPose
visualization_msgs/InteractiveMarkerUpdate
visualization_msgs/Marker
visualization_msgs/MarkerArray
visualization_msgs/MenuEntry

You can now use the above created custom message as the standard messages. For more information on sending and receiving messages, see Exchange Data with ROS 2 Publishers and Subscribers.

Create a publisher to use example_b_msgs/Standalone message.

node = ros2node("/node_1");
pub = ros2publisher(node,"/example_topic","example_b_msgs/Standalone");

Create a subscriber on the same topic.

sub = ros2subscriber(node,"/example_topic");

Create a message and send the message.

custom_msg = ros2message("example_b_msgs/Standalone");
custom_msg.int_property = uint32(12);
custom_msg.string_property='This is ROS 2 custom message example';
send(pub,custom_msg);
pause(3) % Allow a few seconds for the message to arrive

Use LatestMessage field to know the recent message received by the subscriber.

sub.LatestMessage

ans = struct with fields:
        MessageType: 'example_b_msgs/Standalone'
       int_property: 12
    string_property: 'This is ROS 2 custom message example'

Remove the created ROS objects.

clear node pub sub

Replacing Definitions of Built-In Messages with Custom Definitions

MATLAB provides a lot of built-in ROS 2 message types. You can replace the definitions of those message types with new definitions using the same custom message creation workflow detailed above. When you are replacing the definitions of a built-in message package, you must ensure that the custom message package folder contains new definitions (.msg files) for all the message types in the corresponding built-in message package.