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doc/06_perception/13_traffic_light_detection.md

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+# Traffic Light Detection
+
+## Vision Node
+
+For each analyzed image, it is checked whether an object with the ID=9 (traffic light) is detected.
+If that is the case, `process_traffic_lights()` is called which applies the bounding box of the predicition to cut out the found object (e.g. traffic light).
+
+Only if the object is within `min_x`, `max_x` and `min_prob` (probability), it will be published to `"/paf/{self.role_name}/{self.side}/segmented_traffic_light"`.
+
+## TrafficLightNode
+
+The `traffic_light_node.py` file is part of a larger system that handles traffic light detection. It contains a class `TrafficLightNode` that extends from `CompatibleNode`.
+
+This class is responsible for setting up the traffic light detection system and handling the incoming camera images.
+
+### Initialization
+
+The `TrafficLightNode` class is initialized with a name and additional keyword arguments. During initialization, it sets up the following:
+
+- A `CvBridge` instance for converting between ROS image messages and OpenCV images.
+- The role name and side, which are parameters that can be set externally.
+- A `TrafficLightInference` instance for performing traffic light detection.
+
+### Methods
+
+#### `setup_camera_subscriptions()`
+
+This method sets up a subscription to the camera images. It subscribes to the topic `"/paf/{self.role_name}/{self.side}/segmented_traffic_light"` and calls the `handle_camera_image` method whenever a new image message is received.
+
+#### `setup_traffic_light_publishers()`
+
+This method sets up a publisher for the traffic light state. It publishes to the topic `"/paf/{self.role_name}/{self.side}/traffic_light_state"` in the format of `TrafficLightState.msg` which uses an int8-based enum for the traffic light state.
+
+#### `handle_camera_image(image)`
+
+This method is called whenever a new image message is received. It performs traffic light detection by using `traffic_light_inference.py` on the image and publishes the result.
+The result is a `TrafficLightState` message where the state is set to the detected traffic light state (1 for green, 2 for red, 4 for yellow, 0 for unknown).