Update publisher.md

Author: vidurvij-Unity

tutorials/ros_unity_integration/publisher.md

@@ -103,4 +103,120 @@ public class RosPublisherExample : MonoBehaviour
 
 ![](images/tcp_1.gif)
 
+## ROSSPublisherExample script
+
+```csharp
+using RosMessageTypes.RoboticsDemo;
+using UnityEngine;
+using Unity.Robotics.ROSTCPConnector;
+
+/// <summary>
+/// 
+/// </summary>
+public class RosPublisherExample : MonoBehaviour
+{
+ ROSConnection ros;
+ public string topicName = "pos_rot";
+
+ // The game object 
+ public GameObject cube;
+ // Publish the cube's position and rotation every N seconds
+ public float publishMessageFrequency = 0.5f;
+
+ // Used to determine how much time has elapsed since the last message was published
+ private float timeElapsed;
+ 
+ void Start()
+ {
+ // start the ROS connection
+ ros = ROSConnection.instance;
+ }
+
+ private void Update()
+ {
+ timeElapsed += Time.deltaTime;
+
+ if (timeElapsed > publishMessageFrequency)
+ {
+ cube.transform.rotation = Random.rotation;
+
+ MPosRot cubePos = new MPosRot(
+ cube.transform.position.x,
+ cube.transform.position.y,
+ cube.transform.position.z,
+ cube.transform.rotation.x,
+ cube.transform.rotation.y,
+ cube.transform.rotation.z,
+ cube.transform.rotation.w
+ );
+
+ // Finally send the message to server_endpoint.py running in ROS
+ ros.Send(topicName, cubePos);
+
+ timeElapsed = 0;
+ }
+ }
+}
+```
+
+### Import Statements for Publisher and Messages 
+
+```csharp
+using RosMessageTypes.RoboticsDemo;
+using UnityEngine;
+using Unity.Robotics.ROSTCPConnector;
+```
+
+### Instantiating the ROSConnection class in unity
+
+```csharp
+void Start()
+ {
+ // start the ROS connection
+ ros = ROSConnection.instance;
+ }
+```
+To access the APIs needed to communicate with ROS, we need to create a variable of the class ROSConnection in the script. In the rest of the script, we will use `ros` variable to access the APIs needed to publish the message on the desired topic.
+
+### Creating the message
+
+```csharp
+timeElapsed += Time.deltaTime;
+
+ if (timeElapsed > publishMessageFrequency)
+ {
+ cube.transform.rotation = Random.rotation;
+
+ MPosRot cubePos = new MPosRot(
+ cube.transform.position.x,
+ cube.transform.position.y,
+ cube.transform.position.z,
+ cube.transform.rotation.x,
+ cube.transform.rotation.y,
+ cube.transform.rotation.z,
+ cube.transform.rotation.w
+ );
+```
+We create the message by instantiating a new variable of the message class. In this case we are instantiating a new `MPosRot` message class and assigning the current position and rotation of the cube to the message.
+
+### Publishing the message
+
+```csharp
+ros.Send(topicName, cubePos);
+```
+After we have created the message, we use the `Send` API to publish the topic.
+
+### Send API
+```csharp
+public async void Send(string rosTopicName, Message message)
+```
+### Summary
+Its a non-static member of ROSConnection class. Its used to send a ROS message to the desired topic on the ROS machine.
+### Parameters
+ Parameters | Description |
+| ------------- | ------------- |
+| `string rosTopicName` | Name of the topic to which the message will be published |
+| `Message message` | Message to be published on the topic. 
+
+
 Continue to the [ROS Subscriber](subscriber.md) tutorial.