How do I change the QOS in ROS2?

[tom-bu]

Describe your question
Is there a good way to change the QOS to be best effort and a history of 1? Currently, it seems it's only editable by changing the use_system_default_qos parameter, which I'm also not sure where it is being called. When use_system_default_qos is false, the QOS is best effort and history of 5 but a long history with point clouds may be consuming too much memory. When it's set to true, it's set to reliable and a history of 1 but reliable is not appropriate for sensor data. Currently, I have been inspecting the QOS by doing ros2 topic info -v /ouster/points. Is there a QOS parameter file that the driver loads to modify the publisher?

Platform

• OS-1
• ROS2 Humble
• Linux
• x64

[yashmewada9618]

Hi @tom-bu,

The use_system_default_qos param is been called here.

You can create your own rmw QoS policy like this:

static const rmw_qos_profile_t qos = {RMW_QOS_POLICY_HISTORY_KEEP_LAST,
                                          1, // depth
                                          RMW_QOS_POLICY_RELIABILITY_RELIABLE,
                                          RMW_QOS_POLICY_DURABILITY_VOLATILE,
                                          RMW_QOS_DEADLINE_DEFAULT,
                                          RMW_QOS_LIFESPAN_DEFAULT,
                                          RMW_QOS_POLICY_LIVELINESS_SYSTEM_DEFAULT,
                                          RMW_QOS_LIVELINESS_LEASE_DURATION_DEFAULT,
                                          false}; // RMW QOS policy for Ouster lidar, without this the sync won't work
auto lidar_qos = rclcpp::QoS(rclcpp::QoSInitialization::from_rmw(my_custom_qos_profile), my_custom_qos_profile);

Hope this helps.

[Samahu]

Is there a QOS parameter file that the driver loads to modify the publisher?

The only way you can control the QoS currently would be through the use_system_default_qos which can be set through the driver_params.yaml, which allow you to switch between reliable and sensor data. If you need more fine tune control then you need to follow the advice from @yashmewada9618 which requires you to modify the driver code.