content: Add heading controller API

docs/leo-rover/documentation/ros-api.mdx

@@ -26,6 +26,20 @@ image: /img/robots/leo/leo-rover-1.9.webp
   $[\frac{m}{s}]$ (if using the mecanum wheels mode) and `angular.z`
   $[\frac{rad}{s}]$ are used.
 
+- `heading_controller/cmd_vel` ([geometry_msgs/msg/Twist])
+
+  Target velocity for the Rover when using heading control. Publish to this
+  topic instead of `cmd_vel` if you want the Rover to automatically correct its
+  steering and maintain its heading while driving straight or making wide turns.
+  Only `linear.x` $[\frac{m}{s}]$ and `angular.z` $[\frac{rad}{s}]$ are used.
+  This topic is not supported when using mecanum wheels.
+
+  :::warning
+
+  Cannot be used at the same time as other `cmd` topics.
+
+  :::
+
 - `firmware/wheel_{FL,RL,FR,RR}/cmd_pwm_duty` ([std_msgs/msg/Float32])
 
   Target PWM duty cycle for each wheel motor. $[\%]$
@@ -374,6 +388,30 @@ The parameters for `/firmware` node can be overridden by modifying the
   readings. The size of the array must be 3, representing the variances for the
   x, y and z axes.
 
+#### /heading_controller
+
+- `linear_hold_deadband` (type: `float`, default: `0.05`)
+
+  Minimum absolute `linear.x` command required to enable heading hold. If the
+  command is below this value, no heading correction is applied.
+
+- `kp` (type: `float`, default: `15.0`)
+
+  Proportional gain used to convert heading error into `angular.z` correction.
+
+- `max_correction` (type: `float`, default: `1.0`)
+
+  Maximum absolute `angular.z` correction allowed by the heading controller.
+
+- `yaw_deadband` (type: `float`, default: `0.005`)
+
+  Heading error tolerance. Errors within this range produce no correction.
+
+- `angular_hold_deadband` (type: `float`, default: `0.2`)
+
+  Maximum absolute `angular.z` command still treated as heading-hold mode. Above
+  this value, no heading correction is applied.
+
 #### /imu_filter
 
 - `gain_acc` (type: `float`, default: `0.01`)

docs/leo-rover/documentation/specification.mdx

@@ -486,6 +486,13 @@ There are two important software components that don't run as native ROS nodes:
         to communicate with ROS nodes.
       </td>
     </tr>
+    <tr>
+      <td>Heading controller</td>
+      <td>
+        Node that filters the movement commands sent to the robot to maintain a desired heading when driving straight or during
+        wide turns. This helps the robot to better maintain its course, especially if the rubber wheels are slightly deformed.
+      </td>
+    </tr>
 
   </tbody>
 </table>
@@ -538,7 +545,7 @@ This is a user interface that can be accessed via a web browser. It communicates
 with the Rosbridge server using [roslibjs] to access features available on ROS
 topics. The default [leo_ui] provides features such as:
 
-- control of the rover via a keyboard or a virtual joystick,
+- control of the rover via a keyboard, gamepad or a virtual joystick,
 - display of a camera stream from the Web video server, with the ability to
   select the source ROS topic for the video stream,
 - display of the current battery voltage measurement,