Add the ability to control the depth and reliability of the /scan topic

docker-compose.yml

@@ -40,4 +40,6 @@ services:
       - frame_id:=${LIDAR_FRAME_ID:-laser}
       - serial_baudrate:=115200
       - angle_compensate:=true
+      - scan_qos_depth:=${LIDAR_QOS_DEPTH:-2}
+      - scan_qos_reliability:=${LIDAR_QOS_RELIABILITY:-best_effort}
     restart: unless-stopped

lidar/README.md

@@ -70,7 +70,8 @@ git remote add sllidar_ros2 https://github.com/m5p3nc3r/sllidar_ros2.git
 
 | File | Change |
 |---|---|
-| `src/sllidar_node.cpp` | `/scan` publisher QoS set to `BEST_EFFORT` with depth 2. Required for compatibility with Nav2 and RViz2, which subscribe to `/scan` with `BEST_EFFORT`. The upstream default (`RELIABLE`) causes those consumers to receive no data. |
+| `src/sllidar_node.cpp` | `/scan` publisher QoS made configurable via `scan_qos_depth` (int) and `scan_qos_reliability` (`best_effort`\|`reliable`) parameters. Defaults to `best_effort`, depth 2 — required for Nav2 / RViz2 compatibility. |
+| `launch/sllidar_a1_launch.py` | Exposes `scan_qos_depth` and `scan_qos_reliability` as launch arguments. |
 
 The upstream Slamtec repository is at:
 

lidar/sllidar_ros2/launch/sllidar_a1_launch.py

@@ -18,6 +18,8 @@ def generate_launch_description():
     inverted = LaunchConfiguration('inverted', default='false')
     angle_compensate = LaunchConfiguration('angle_compensate', default='true')
     scan_mode = LaunchConfiguration('scan_mode', default='Sensitivity')
+    scan_qos_depth = LaunchConfiguration('scan_qos_depth', default='10')
+    scan_qos_reliability = LaunchConfiguration('scan_qos_reliability', default='reliable')
     
     return LaunchDescription([
 
@@ -55,17 +57,28 @@ def generate_launch_description():
             default_value=scan_mode,
             description='Specifying scan mode of lidar'),
 
+        DeclareLaunchArgument(
+            'scan_qos_depth',
+            default_value=scan_qos_depth,
+            description='Queue depth for the /scan publisher'),
+
+        DeclareLaunchArgument(
+            'scan_qos_reliability',
+            default_value=scan_qos_reliability,
+            description='Reliability policy for the /scan publisher: best_effort or reliable'),
 
         Node(
             package='sllidar_ros2',
             executable='sllidar_node',
             name='sllidar_node',
-            parameters=[{'channel_type':channel_type,
+            parameters=[{'channel_type': channel_type,
                          'serial_port': serial_port,
                          'serial_baudrate': serial_baudrate,
                          'frame_id': frame_id,
                          'inverted': inverted,
-                         'angle_compensate': angle_compensate}],
+                         'angle_compensate': angle_compensate,
+                         'scan_qos_depth': scan_qos_depth,
+                         'scan_qos_reliability': scan_qos_reliability}],
             output='screen'),
     ])
 

lidar/sllidar_ros2/src/sllidar_node.cpp

@@ -58,9 +58,24 @@ class SLlidarNode : public rclcpp::Node
     SLlidarNode()
     : Node("sllidar_node")
     {
+        // QoS parameters must be declared here because the publisher is created
+        // before init_param() is called in work_loop().
+        this->declare_parameter<int>("scan_qos_depth", 2);
+        this->declare_parameter<std::string>("scan_qos_reliability", "best_effort");
 
-      scan_pub = this->create_publisher<sensor_msgs::msg::LaserScan>("scan", rclcpp::QoS(rclcpp::KeepLast(2)).best_effort());
+        int qos_depth;
+        std::string qos_reliability;
+        this->get_parameter_or<int>("scan_qos_depth", qos_depth, 2);
+        this->get_parameter_or<std::string>("scan_qos_reliability", qos_reliability, "best_effort");
 
+        auto qos = rclcpp::QoS(rclcpp::KeepLast(qos_depth));
+        if (qos_reliability == "best_effort") {
+            qos.best_effort();
+        } else {
+            qos.reliable();
+        }
+
+        scan_pub = this->create_publisher<sensor_msgs::msg::LaserScan>("scan", qos);
     }
 
   private:    

troubleshooting.md

@@ -0,0 +1,23 @@
+# Troubleshooting
+
+## No sensor data is received on topic
+
+Data is sent over UDP, and if the sensor data exceeds the maximum receive buffer size of the network stack, the data frame will be silently discarded.
+
+The solution is to increase the receive memory buffer size
+
+```bash
+sudo sysctl -w net.core.rmem_max=2097152
+sudo sysctl -w net.core.rmem_default=2097152
+```
+
+## Discarding message because the queue is full
+
+If you are getting a message like: 
+```
+ [rviz]: Message Filter dropping message: frame 'laser' at time 1776876114.823 for reason 'discarding message because the queue is full'
+ ```
+
+ This could be because there is no `/tf` topic available.  This topic is used to describe the relationship between coordinate systems (robot position, lidar position, camera position etc).
+
+ If this is the case, you can changet the fixed frame reference to the lidar itself.  Change the `Global Options -> Fixed Frame` option from `map` to `laser` to tell the system to use the laser as the base of all transforms.