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Add creating new message tutorial (#191)
* Initial tutorial * Update * Update _docs/tutorials/core/create_new_type/index.md Co-authored-by: Jose Antonio Moral <joseantoniomoralparras@gmail.com> * Update _docs/tutorials/core/create_new_type/index.md Co-authored-by: Jose Antonio Moral <joseantoniomoralparras@gmail.com> * Update _docs/tutorials/core/create_new_type/index.md Co-authored-by: Jose Antonio Moral <joseantoniomoralparras@gmail.com> * Add type composition * Update _docs/tutorials/core/create_new_type/index.md Co-authored-by: FranFin <58737168+FranFin@users.noreply.github.com> * Update _docs/tutorials/core/create_new_type/index.md Co-authored-by: FranFin <58737168+FranFin@users.noreply.github.com> * Update _docs/tutorials/core/create_new_type/index.md Co-authored-by: FranFin <58737168+FranFin@users.noreply.github.com> * Update _docs/tutorials/core/create_new_type/index.md Co-authored-by: FranFin <58737168+FranFin@users.noreply.github.com> * Update index.md * Update _docs/tutorials/core/create_new_type/index.md Co-authored-by: FranFin <58737168+FranFin@users.noreply.github.com> Co-authored-by: Jose Antonio Moral <joseantoniomoralparras@gmail.com> Co-authored-by: FranFin <58737168+FranFin@users.noreply.github.com>
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‎_data/docs.yml‎

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- tutorials/core/first_application_rtos
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- tutorials/core/programming_rcl_rclc
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- tutorials/core/microxrcedds_rmw_configuration
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- tutorials/core/create_new_type
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- title: Advanced Tutorials
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docs:

‎_docs/tutorials/core/create_new_type/index.md‎

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---
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title: How to create a new micro-ROS type
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permalink: /docs/tutorials/core/create_new_type/
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---
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This tutorial starts in a previously created micro-ROS environment. Check [**First micro-ROS application on an RTOS**](../first_application_rtos/) for instructions about how to create a micro-ROS environment for embedded platforms.
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Once your micro-ROS workspace is created, go to `firmware/mcu_ws` and run the package creating command:
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```bash
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cd firmware/mcu_ws
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ros2 pkg create --build-type ament_cmake my_custom_message
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cd my_custom_message
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mkdir msg
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touch msg/MyCustomMessage.msg
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```
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In the autogenerated `CMakeLists.txt` file you should add the following lines just before `ament_package()`:
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```cmake
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...
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find_package(rosidl_default_generators REQUIRED)
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rosidl_generate_interfaces(${PROJECT_NAME}
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"msg/MyCustomMessage.msg"
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)
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...
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```
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In the autogenerated `package.xml` file you should add the following lines:
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```xml
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...
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<build_depend>rosidl_default_generators</build_depend>
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<exec_depend>rosidl_default_runtime</exec_depend>
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<member_of_group>rosidl_interface_packages</member_of_group>
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...
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```
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The content of the `msg/MyCustomMessage.msg` file contains your message defintion. For example, let's include these fields:
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```
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bool bool_test
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byte byte_test
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char char_test
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float32 float32_test
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float64 double_test
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int8 int8_test
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uint8 uint8_test
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int16 int16_test
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uint16 uint16_test
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int32 int32_test
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uint32 uint32_test
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int64 int64_test
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uint64 uint64_test
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```
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Now, you can build your micro-ROS workspace as usual. As explained in [**First micro-ROS application on an RTOS**](../first_application_rtos/), the `ros2 run micro_ros_setup build_firmware.sh` command will build all packages located inside `mcu_ws`.
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In your micro-ROS application code, you can use your new message type as usual:
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```c
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#include <my_custom_message/msg/my_custom_message.h>
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...
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my_custom_message__msg__MyCustomMessage msg;
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msg.byte_test = 3;
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msg.uint32_test = 42;
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...
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rclc_publisher_init_default(&publisher, &node, ROSIDL_GET_MSG_TYPE_SUPPORT(my_custom_message, msg, MyCustomMessage), "my_custom_publisher");
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rcl_publish(&publisher, &msg, NULL);
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...
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```
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You can find further information in the [ROS 2 Create custom ROS 2 msg and srv files](https://index.ros.org/doc/ros2/Tutorials/Custom-ROS2-Interfaces).
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## Using type composition
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It is possible to create custom types that include members from another ROS 2 message types packages. For example let's add a member with type `Point32` from the ROS 2 package `geometry_msgs`.
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First of all, you have to include the dependency in the `CMakeLists.txt`:
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```cmake
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...
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find_package(rosidl_default_generators REQUIRED)
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find_package(geometry_msgs REQUIRED)
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rosidl_generate_interfaces(${PROJECT_NAME}
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"msg/MyCustomMessage.msg"
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)
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...
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```
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Also, include the dependency in `package.xml`:
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```xml
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...
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<build_depend>rosidl_default_generators</build_depend>
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<exec_depend>rosidl_default_runtime</exec_depend>
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<member_of_group>rosidl_interface_packages</member_of_group>
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<depend>geometry_msgs</depend>
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...
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```
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The message definition in `msg/MyCustomMessage.msg` can now include types from the `geometry_msgs` package:
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```
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...
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int64 int64_test
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uint64 uint64_test
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geometry_msgs/Point32 point32_test
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```
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And finally, in your code you can access this new member of your custom type:
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```c
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#include <my_custom_message/msg/my_custom_message.h>
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...
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my_custom_message__msg__MyCustomMessage msg;
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msg.byte_test = 3;
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msg.uint32_test = 42;
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msg.point32_test.x = 1.23;
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msg.point32_test.y = 2.31;
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msg.point32_test.z = 3.12;
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...
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```

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