Update sensors.md doc

ionic/sensors.md

@@ -86,7 +86,7 @@ The last command listens to the messages sent over the `/imu` topic. The IMU dat
 
 ![Imu_message](tutorials/sensors/imu_msgs.png)
 
-Move your robot forward using the keyboard up key. You should see the sensor values changing.
+Move your robot forward using the keyboard up key. To do so, don't forget to enable the Key Publisher Plugin. You should see the sensor values changing.
 
 ## Contact sensor
 
@@ -315,24 +315,25 @@ To do that, we'll write a short C++ program that listens to
 the sensor data and sends velocity commands to the robot.
 This program is called a node. We will build a node that subscribes
 to the `/lidar` topic and reads its data.
-Have a look at this [tutorial](https://gazebosim.org/api/transport/9.0/messages.html)
+Have a look at this [tutorial](https://gazebosim.org/api/transport/14/messages.html)
 to learn how to build a `publisher` and a `subscriber` node.
 You can download the finished node for this demo from [here](https://github.com/gazebosim/docs/blob/master/ionic/tutorials/sensors/lidar_node.cc).
 
 #### The lidar_node
 
 ```cpp
-gz::transport::Node node;
 std::string topic_pub = "/cmd_vel";
-gz::msgs::Twist data;
+gz::transport::Node node;
 auto pub = node.Advertise<gz::msgs::Twist>(topic_pub);
 ```
 
-We declare a `node` which will publish to `cmd_vel` topic and defined the message type `Twist`. Then advertise our node.
+We declare a `node` which will publish to `cmd_vel` topic. Then advertise our node.
 
 ```cpp
 void cb(const gz::msgs::LaserScan &_msg)
 {
+  gz::msgs::Twist data;
+
   bool allMore = true;
   for (int i = 0; i < _msg.ranges_size(); i++)
   {
@@ -362,11 +363,11 @@ If so we publish a message to our car to move forward. Otherwise we make the rob
 ```cpp
 int main(int argc, char **argv)
 {
-    std::string topic = "/lidar";
+    std::string topic_sub = "/lidar";
     // Subscribe to a topic by registering a callback.
-    if (!node.Subscribe(topic, cb))
+    if (!node.Subscribe(topic_sub, cb))
     {
-        std::cerr << "Error subscribing to topic [" << topic << "]" << std::endl;
+        std::cerr << "Error subscribing to topic [" << topic_sub << "]" << std::endl;
         return -1;
     }