Using ros_gz_bridge

Using `ros_gz_bridge`#

Added in version Jazzy: This section.

Warning

This topic is under construction and this might not even be its final form. Please feel free to open an issue if you spot any typos or other problems.

Sensors#

gz.msgs.Image#

In a previous section, we have seen that the Gazebo topic /rgbd_camera/image exists and has transport type gz.msgs.Image. Looking at the pairing table, we notice that the pairing ROS2 message type is sensor_msgs/msg/Image.

We can run, therefore in one terminal, the following command.

ros2 run ros_gz_bridge \
parameter_bridge \
/rgbd_camera/image@sensor_msgs/msg/Image[gz.msgs.Image

To show the images, we can use rqt_image_view. Notice that the internal Gazebo topic name will be replicated into a ROS2 topic with the same name.

ros2 run rqt_image_view rqt_image_view /rgbd_camera/image

This will show the image obtained from Gazebo in rqt_image_view, effectively showing that these two are paired.

Exercises

Can you do the same for the /depth_camera or /thermal_camera internal Gazebo topic available in the same scene? What steps would you take to show the images available in Gazebo into rqt_image_view?

gz.msgs.LaserScan#

We have already listed the Gazebo topics for this scene, so we know that there is a topic called /lidar. We can obtain the related information with the following command.

gz topic -i --topic /lidar

This will output the following.

Publishers [Address, Message Type]:
  tcp://172.16.191.128:40679, gz.msgs.LaserScan
No subscribers on topic [/lidar]

By looking at the pairing table, we find that gz.msgs.LaserScan should be paired with a sensor_msgs/msg/LaserScan. Therefore, we can run the bridge as follows.

ros2 run ros_gz_bridge \
parameter_bridge \
/lidar@sensor_msgs/msg/LaserScan[gz.msgs.LaserScan

One convenient way to visualise this messages is through rviz2. We can do so as follows.

ros2 run rviz2 rviz2 -f camera_with_lidar/link/gpu_lidar

Note

We are starting rviz2 with the reference frame camera_with_lidar/link/gpu_lidar because that is the frame shown in the topic /lidar.

We can then define the proper rviz2 view so be able to visualise the laser scan results.

Add ‣ rviz_default_plugins ‣ LaserScan ‣ OK.
Displays ‣ LaserScan ‣ topic ‣ lidar ‣ Press ENTER.

Getting pose information#

One important aspect of entities in any simulation is their pose. We must be able to obtain poses to define the behavior of our robots. For instance, if a box in a simulation moves, the controller might need this information to define evasive maneuvers.

The most basic manner to be able to obtain the pose of an entity in Gazebo from an external program is to add the following to each model, in the .sdf scene.

<plugin
        filename="gz-sim-pose-publisher-system"
        name="gz::sim::systems::PosePublisher">
    <publish_link_pose>false</publish_link_pose>
    <publish_collision_pose>false</publish_collision_pose>
    <publish_visual_pose>false</publish_visual_pose>
    <publish_nested_model_pose>true</publish_nested_model_pose>
</plugin>

Note

Settings will vary for more advanced use, but for basic shapes this will be enough.

To show how this works, let us create a folder for our modified shapes.sdf scene.

mkdir -p ~/gazebo_tutorial_workspace/scenes
cd ~/gazebo_tutorial_workspace/scenes

In this case, the file is quite large, so I suggest downloading shapes_with_pose_publisher.sdf and adding it to the folder above.

shapes_with_pose_publisher.sdf

Contents of shapes_with_pose_publisher.sdf

You will note that this is simply the default shapes.sdf with the plugin added to each entity.

<?xml version="1.0" ?>
<sdf version="1.11">
    <!--
      Try moving a model using the command in the following CDATA block::
    -->
    <![CDATA[
    gz service -s /world/shapes/set_pose \
               --reqtype gz.msgs.Pose --reptype gz.msgs.Boolean \
               --timeout 300 --req 'name: "box", position: {z: 5.0}'
  ]]>
    <world name="shapes_with_pose_publisher">

        <scene>
            <ambient>1.0 1.0 1.0</ambient>
            <background>0.8 0.8 0.8</background>
        </scene>

        <light type="directional" name="sun">
            <cast_shadows>true</cast_shadows>
            <pose>0 0 10 0 0 0</pose>
            <diffuse>0.8 0.8 0.8 1</diffuse>
            <specular>0.2 0.2 0.2 1</specular>
            <attenuation>
                <range>1000</range>
                <constant>0.9</constant>
                <linear>0.01</linear>
                <quadratic>0.001</quadratic>
            </attenuation>
            <direction>-0.5 0.1 -0.9</direction>
        </light>

        <model name="ground_plane">
            <static>true</static>
            <link name="link">
                <collision name="collision">
                    <geometry>
                        <plane>
                            <normal>0 0 1</normal>
                            <size>100 100</size>
                        </plane>
                    </geometry>
                </collision>
                <visual name="visual">
                    <geometry>
                        <plane>
                            <normal>0 0 1</normal>
                            <size>100 100</size>
                        </plane>
                    </geometry>
                    <material>
                        <ambient>0.8 0.8 0.8 1</ambient>
                        <diffuse>0.8 0.8 0.8 1</diffuse>
                        <specular>0.8 0.8 0.8 1</specular>
                    </material>
                </visual>
            </link>
        </model>

        <model name="box">
            <pose>0 0 0.5 0 0 0</pose>
            <link name="box_link">
                <inertial>
                    <inertia>
                        <ixx>0.16666</ixx>
                        <ixy>0</ixy>
                        <ixz>0</ixz>
                        <iyy>0.16666</iyy>
                        <iyz>0</iyz>
                        <izz>0.16666</izz>
                    </inertia>
                    <mass>1.0</mass>
                </inertial>
                <collision name="box_collision">
                    <geometry>
                        <box>
                            <size>1 1 1</size>
                        </box>
                    </geometry>
                </collision>

                <visual name="box_visual">
                    <geometry>
                        <box>
                            <size>1 1 1</size>
                        </box>
                    </geometry>
                    <material>
                        <ambient>1 0 0 1</ambient>
                        <diffuse>1 0 0 1</diffuse>
                        <specular>1 0 0 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>

        <model name="cylinder">
            <pose>0 -1.5 0.5 0 0 0</pose>
            <link name="cylinder_link">
                <inertial>
                    <inertia>
                        <ixx>0.1458</ixx>
                        <ixy>0</ixy>
                        <ixz>0</ixz>
                        <iyy>0.1458</iyy>
                        <iyz>0</iyz>
                        <izz>0.125</izz>
                    </inertia>
                    <mass>1.0</mass>
                </inertial>
                <collision name="cylinder_collision">
                    <geometry>
                        <cylinder>
                            <radius>0.5</radius>
                            <length>1.0</length>
                        </cylinder>
                    </geometry>
                </collision>

                <visual name="cylinder_visual">
                    <geometry>
                        <cylinder>
                            <radius>0.5</radius>
                            <length>1.0</length>
                        </cylinder>
                    </geometry>
                    <material>
                        <ambient>0 1 0 1</ambient>
                        <diffuse>0 1 0 1</diffuse>
                        <specular>0 1 0 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>

        <model name="sphere">
            <pose>0 1.5 0.5 0 0 0</pose>
            <link name="sphere_link">
                <inertial>
                    <inertia>
                        <ixx>0.1</ixx>
                        <ixy>0</ixy>
                        <ixz>0</ixz>
                        <iyy>0.1</iyy>
                        <iyz>0</iyz>
                        <izz>0.1</izz>
                    </inertia>
                    <mass>1.0</mass>
                </inertial>
                <collision name="sphere_collision">
                    <geometry>
                        <sphere>
                            <radius>0.5</radius>
                        </sphere>
                    </geometry>
                </collision>

                <visual name="sphere_visual">
                    <geometry>
                        <sphere>
                            <radius>0.5</radius>
                        </sphere>
                    </geometry>
                    <material>
                        <ambient>0 0 1 1</ambient>
                        <diffuse>0 0 1 1</diffuse>
                        <specular>0 0 1 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>

        <model name="capsule">
            <pose>0 -3.0 0.5 0 0 0</pose>
            <link name="capsule_link">
                <inertial>
                    <inertia>
                        <ixx>0.074154</ixx>
                        <ixy>0</ixy>
                        <ixz>0</ixz>
                        <iyy>0.074154</iyy>
                        <iyz>0</iyz>
                        <izz>0.018769</izz>
                    </inertia>
                    <mass>1.0</mass>
                </inertial>
                <collision name="capsule_collision">
                    <geometry>
                        <capsule>
                            <radius>0.2</radius>
                            <length>0.6</length>
                        </capsule>
                    </geometry>
                </collision>
                <visual name="capsule_visual">
                    <geometry>
                        <capsule>
                            <radius>0.2</radius>
                            <length>0.6</length>
                        </capsule>
                    </geometry>
                    <material>
                        <ambient>1 1 0 1</ambient>
                        <diffuse>1 1 0 1</diffuse>
                        <specular>1 1 0 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>

        <model name="ellipsoid">
            <pose>0 3.0 0.5 0 0 0</pose>
            <link name="ellipsoid_link">
                <inertial>
                    <inertia>
                        <ixx>0.068</ixx>
                        <ixy>0</ixy>
                        <ixz>0</ixz>
                        <iyy>0.058</iyy>
                        <iyz>0</iyz>
                        <izz>0.026</izz>
                    </inertia>
                    <mass>1.0</mass>
                </inertial>
                <collision name="ellipsoid_collision">
                    <geometry>
                        <ellipsoid>
                            <radii>0.2 0.3 0.5</radii>
                        </ellipsoid>
                    </geometry>
                </collision>
                <visual name="ellipsoid_visual">
                    <geometry>
                        <ellipsoid>
                            <radii>0.2 0.3 0.5</radii>
                        </ellipsoid>
                    </geometry>
                    <material>
                        <ambient>1 0 1 1</ambient>
                        <diffuse>1 0 1 1</diffuse>
                        <specular>1 0 1 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>

        <model name="cone">
            <pose>0 4.5 0.5 0 0 0</pose>
            <link name="cone_link">
                <inertial auto="true">
                    <density>1</density>
                </inertial>
                <collision name="cone_collision">
                    <geometry>
                        <cone>
                            <radius>0.5</radius>
                            <length>1.0</length>
                        </cone>
                    </geometry>
                </collision>

                <visual name="cone_visual">
                    <geometry>
                        <cone>
                            <radius>0.5</radius>
                            <length>1.0</length>
                        </cone>
                    </geometry>
                    <material>
                        <ambient>1 0.47 0 1</ambient>
                        <diffuse>1 0.47 0 1</diffuse>
                        <specular>1 0.47 0 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>
    </world>
</sdf>

We open Gazebo with this scene, as follows, then run the simulation by clicking the run button.

gz sim ~/gazebo_tutorial_workspace/scenes/shapes_with_pose_publisher.sdf

Note

Don’t forget to run the simulation otherwise most information will not be available.

The plugin for each entity will create a pose topic. We can verify that with the following command.

gz topic -l

The result will be as follows, where the relevant topics are highlighted.

/clock
/gazebo/resource_paths
/gui/camera/pose
/gui/currently_tracked
/gui/track
/model/box/pose
/model/capsule/pose
/model/cone/pose
/model/cylinder/pose
/model/ellipsoid/pose
/model/sphere/pose
/stats
/world/shapes_with_pose_publisher/clock
/world/shapes_with_pose_publisher/dynamic_pose/info
/world/shapes_with_pose_publisher/pose/info
/world/shapes_with_pose_publisher/scene/deletion
/world/shapes_with_pose_publisher/scene/info
/world/shapes_with_pose_publisher/state
/world/shapes_with_pose_publisher/stats
/world/shapes_with_pose_publisher/light_config
/world/shapes_with_pose_publisher/material_color

As always, we can investigate the Gazebo type these topics, as we expect all of them to be the same as they come from the same plugin. Let’s choose the box as it’s the first entity on the list.

We use the following command.

gz topic -i --topic /model/box/pose

It will output the type.

Publishers [Address, Message Type]:
  tcp://172.16.191.128:41611, gz.msgs.Pose
No subscribers on topic [/model/box/pose]

Because this will be an unilateral bridge from Gazebo to ROS2, we use the [ instead of @ as follows.

ros2 run ros_gz_bridge \
parameter_bridge \
/model/box/pose@geometry_msgs/msg/Pose[gz.msgs.Pose

We can see the contents of the topic with the following command. It will show the real-time information of the entity, even if you move it around within Gazebo.

ros2 topic echo /model/box/pose

We can see how fast your bridge is running with the usual command below.

ros2 topic hz /model/box/pose

Depending on the quality of your machine, your results will very, but you should expect this frequency to be quite high.

average rate: 799.066
    min: 0.000s max: 0.009s std dev: 0.00142s window: 800
average rate: 824.706
    min: 0.000s max: 0.009s std dev: 0.00129s window: 1652
average rate: 811.552
    min: 0.000s max: 0.010s std dev: 0.00131s window: 2439
average rate: 815.633
    min: 0.000s max: 0.010s std dev: 0.00129s window: 3267

Exercises

I have shown how to obtain the pose of the box entity. This scene has other five topics, namely.

/model/capsule/pose
/model/cone/pose
/model/cylinder/pose
/model/ellipsoid/pose
/model/sphere/pose

Can you run the bridge of each one of these and see the results of each of these entities?

Getting transforms#

Warning

You’ll notice that each scene creates a Gazebo topic called /world/<SCENE>/pose/info where <SCENE> is the name of the active scene. Although this publishes useful information when checking through Gazebo topics, it does not play well with ros_gz_bridge. You can get the transform information without the headers, which in ROS2 is not useful.

See also

gazebosim/ros_gz#172

Integration with other parts of ROS2 is important, therefore it could be useful to have all poses of relevant objects available for tf2. In this case, we need to modify the message that is published by Gazebo, but otherwise there is no big difference.

Our use of gz::sim::systems::PosePublisher will be slightly modified to have <use_pose_vector_msg>true</use_pose_vector_msg>, highlighted below.

<plugin
        filename="gz-sim-pose-publisher-system"
        name="gz::sim::systems::PosePublisher">
    <use_pose_vector_msg>true</use_pose_vector_msg>
    <publish_link_pose>false</publish_link_pose>
    <publish_collision_pose>false</publish_collision_pose>
    <publish_visual_pose>false</publish_visual_pose>
    <publish_nested_model_pose>true</publish_nested_model_pose>
</plugin>

Add the following file to your ~/gazebo_tutorial_workspace/scenes folder.

shapes_with_tf2_publisher.sdf

Contents of shapes_with_tf2_publisher.sdf

This is shapes_with_pose_publisher.sdf with one additional line in each gz::sim::systems::PosePublisher plugin.

<?xml version="1.0" ?>
<sdf version="1.11">
    <!--
      Try moving a model using the command in the following CDATA block::
    -->
    <![CDATA[
    gz service -s /world/shapes/set_pose \
               --reqtype gz.msgs.Pose --reptype gz.msgs.Boolean \
               --timeout 300 --req 'name: "box", position: {z: 5.0}'
  ]]>
    <world name="shapes_with_tf2_publisher">

        <scene>
            <ambient>1.0 1.0 1.0</ambient>
            <background>0.8 0.8 0.8</background>
        </scene>

        <light type="directional" name="sun">
            <cast_shadows>true</cast_shadows>
            <pose>0 0 10 0 0 0</pose>
            <diffuse>0.8 0.8 0.8 1</diffuse>
            <specular>0.2 0.2 0.2 1</specular>
            <attenuation>
                <range>1000</range>
                <constant>0.9</constant>
                <linear>0.01</linear>
                <quadratic>0.001</quadratic>
            </attenuation>
            <direction>-0.5 0.1 -0.9</direction>
        </light>

        <model name="ground_plane">
            <static>true</static>
            <link name="link">
                <collision name="collision">
                    <geometry>
                        <plane>
                            <normal>0 0 1</normal>
                            <size>100 100</size>
                        </plane>
                    </geometry>
                </collision>
                <visual name="visual">
                    <geometry>
                        <plane>
                            <normal>0 0 1</normal>
                            <size>100 100</size>
                        </plane>
                    </geometry>
                    <material>
                        <ambient>0.8 0.8 0.8 1</ambient>
                        <diffuse>0.8 0.8 0.8 1</diffuse>
                        <specular>0.8 0.8 0.8 1</specular>
                    </material>
                </visual>
            </link>
        </model>

        <model name="box">
            <pose>0 0 0.5 0 0 0</pose>
            <link name="box_link">
                <inertial>
                    <inertia>
                        <ixx>0.16666</ixx>
                        <ixy>0</ixy>
                        <ixz>0</ixz>
                        <iyy>0.16666</iyy>
                        <iyz>0</iyz>
                        <izz>0.16666</izz>
                    </inertia>
                    <mass>1.0</mass>
                </inertial>
                <collision name="box_collision">
                    <geometry>
                        <box>
                            <size>1 1 1</size>
                        </box>
                    </geometry>
                </collision>

                <visual name="box_visual">
                    <geometry>
                        <box>
                            <size>1 1 1</size>
                        </box>
                    </geometry>
                    <material>
                        <ambient>1 0 0 1</ambient>
                        <diffuse>1 0 0 1</diffuse>
                        <specular>1 0 0 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <use_pose_vector_msg>true</use_pose_vector_msg>
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>

        <model name="cylinder">
            <pose>0 -1.5 0.5 0 0 0</pose>
            <link name="cylinder_link">
                <inertial>
                    <inertia>
                        <ixx>0.1458</ixx>
                        <ixy>0</ixy>
                        <ixz>0</ixz>
                        <iyy>0.1458</iyy>
                        <iyz>0</iyz>
                        <izz>0.125</izz>
                    </inertia>
                    <mass>1.0</mass>
                </inertial>
                <collision name="cylinder_collision">
                    <geometry>
                        <cylinder>
                            <radius>0.5</radius>
                            <length>1.0</length>
                        </cylinder>
                    </geometry>
                </collision>

                <visual name="cylinder_visual">
                    <geometry>
                        <cylinder>
                            <radius>0.5</radius>
                            <length>1.0</length>
                        </cylinder>
                    </geometry>
                    <material>
                        <ambient>0 1 0 1</ambient>
                        <diffuse>0 1 0 1</diffuse>
                        <specular>0 1 0 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <use_pose_vector_msg>true</use_pose_vector_msg>
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>

        <model name="sphere">
            <pose>0 1.5 0.5 0 0 0</pose>
            <link name="sphere_link">
                <inertial>
                    <inertia>
                        <ixx>0.1</ixx>
                        <ixy>0</ixy>
                        <ixz>0</ixz>
                        <iyy>0.1</iyy>
                        <iyz>0</iyz>
                        <izz>0.1</izz>
                    </inertia>
                    <mass>1.0</mass>
                </inertial>
                <collision name="sphere_collision">
                    <geometry>
                        <sphere>
                            <radius>0.5</radius>
                        </sphere>
                    </geometry>
                </collision>

                <visual name="sphere_visual">
                    <geometry>
                        <sphere>
                            <radius>0.5</radius>
                        </sphere>
                    </geometry>
                    <material>
                        <ambient>0 0 1 1</ambient>
                        <diffuse>0 0 1 1</diffuse>
                        <specular>0 0 1 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <use_pose_vector_msg>true</use_pose_vector_msg>
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>

        <model name="capsule">
            <pose>0 -3.0 0.5 0 0 0</pose>
            <link name="capsule_link">
                <inertial>
                    <inertia>
                        <ixx>0.074154</ixx>
                        <ixy>0</ixy>
                        <ixz>0</ixz>
                        <iyy>0.074154</iyy>
                        <iyz>0</iyz>
                        <izz>0.018769</izz>
                    </inertia>
                    <mass>1.0</mass>
                </inertial>
                <collision name="capsule_collision">
                    <geometry>
                        <capsule>
                            <radius>0.2</radius>
                            <length>0.6</length>
                        </capsule>
                    </geometry>
                </collision>
                <visual name="capsule_visual">
                    <geometry>
                        <capsule>
                            <radius>0.2</radius>
                            <length>0.6</length>
                        </capsule>
                    </geometry>
                    <material>
                        <ambient>1 1 0 1</ambient>
                        <diffuse>1 1 0 1</diffuse>
                        <specular>1 1 0 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <use_pose_vector_msg>true</use_pose_vector_msg>
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>

        <model name="ellipsoid">
            <pose>0 3.0 0.5 0 0 0</pose>
            <link name="ellipsoid_link">
                <inertial>
                    <inertia>
                        <ixx>0.068</ixx>
                        <ixy>0</ixy>
                        <ixz>0</ixz>
                        <iyy>0.058</iyy>
                        <iyz>0</iyz>
                        <izz>0.026</izz>
                    </inertia>
                    <mass>1.0</mass>
                </inertial>
                <collision name="ellipsoid_collision">
                    <geometry>
                        <ellipsoid>
                            <radii>0.2 0.3 0.5</radii>
                        </ellipsoid>
                    </geometry>
                </collision>
                <visual name="ellipsoid_visual">
                    <geometry>
                        <ellipsoid>
                            <radii>0.2 0.3 0.5</radii>
                        </ellipsoid>
                    </geometry>
                    <material>
                        <ambient>1 0 1 1</ambient>
                        <diffuse>1 0 1 1</diffuse>
                        <specular>1 0 1 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <use_pose_vector_msg>true</use_pose_vector_msg>
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>

        <model name="cone">
            <pose>0 4.5 0.5 0 0 0</pose>
            <link name="cone_link">
                <inertial auto="true">
                    <density>1</density>
                </inertial>
                <collision name="cone_collision">
                    <geometry>
                        <cone>
                            <radius>0.5</radius>
                            <length>1.0</length>
                        </cone>
                    </geometry>
                </collision>

                <visual name="cone_visual">
                    <geometry>
                        <cone>
                            <radius>0.5</radius>
                            <length>1.0</length>
                        </cone>
                    </geometry>
                    <material>
                        <ambient>1 0.47 0 1</ambient>
                        <diffuse>1 0.47 0 1</diffuse>
                        <specular>1 0.47 0 1</specular>
                    </material>
                </visual>
            </link>

            <plugin
                    filename="gz-sim-pose-publisher-system"
                    name="gz::sim::systems::PosePublisher">
                <use_pose_vector_msg>true</use_pose_vector_msg>
                <publish_link_pose>false</publish_link_pose>
                <publish_collision_pose>false</publish_collision_pose>
                <publish_visual_pose>false</publish_visual_pose>
                <publish_nested_model_pose>true</publish_nested_model_pose>
            </plugin>

        </model>
    </world>
</sdf>

We open Gazebo with this scene, as follows, then run the simulation by clicking the run button.

gz sim ~/gazebo_tutorial_workspace/scenes/shapes_with_tf2_publisher.sdf

Note

Don’t forget to run the simulation otherwise most information will not be available.

In another terminal, we can check the type of message being used to publish poses.

gz topic -i --topic /model/box/pose

The output will be similar to the one below. Our modification in the plugin makes the Gazebo topic use a different message type, gz.msgs.Pose_V.

Publishers [Address, Message Type]:
  tcp://172.16.191.128:34555, gz.msgs.Pose_V
Subscribers [Address, Message Type]:
  tcp://172.16.191.128:37389, gz.msgs.Pose_V

The idea now is to bridge that type of message with tf2. Beyond simply bridging the topics, we have to make sure that these two points are correct.

All transforms are published to a topic named /tf, for compatibility with tf2.
The clock used in ROS2 matches the one used in Gazebo. This will make sure that when we look up transforms the timestamp will make sense.

Now, because we have seven topics to bridge, it would not be practical to have that done through the command line. In addition we need topics that have different names in Gazebo and ROS2.

We can take advantage of .yaml configuration files that are supported by ros_gz_bridge.

To show how this works, let us create a folder for our .yaml bridge files.

mkdir -p ~/gazebo_tutorial_workspace/bridge_config
cd ~/gazebo_tutorial_workspace/bridge_config

We add the following file to the newly created folder. The /clock bridge and the /tf bridge elements that are new are highlighted.

transforms.yaml

- ros_topic_name: "/clock"
  gz_topic_name: "/clock"
  ros_type_name: "rosgraph_msgs/msg/Clock"
  gz_type_name: "gz.msgs.Clock"
  direction: GZ_TO_ROS

- ros_topic_name: "/tf"
  gz_topic_name: "/model/box/pose"
  ros_type_name: "tf2_msgs/msg/TFMessage"
  gz_type_name: "gz.msgs.Pose_V"
  direction: GZ_TO_ROS

- ros_topic_name: "/tf"
  gz_topic_name: "/model/capsule/pose"
  ros_type_name: "tf2_msgs/msg/TFMessage"
  gz_type_name: "gz.msgs.Pose_V"
  direction: GZ_TO_ROS

- ros_topic_name: "/tf"
  gz_topic_name: "/model/cone/pose"
  ros_type_name: "tf2_msgs/msg/TFMessage"
  gz_type_name: "gz.msgs.Pose_V"
  direction: GZ_TO_ROS

- ros_topic_name: "/tf"
  gz_topic_name: "/model/cylinder/pose"
  ros_type_name: "tf2_msgs/msg/TFMessage"
  gz_type_name: "gz.msgs.Pose_V"
  direction: GZ_TO_ROS

- ros_topic_name: "/tf"
  gz_topic_name: "/model/ellipsoid/pose"
  ros_type_name: "tf2_msgs/msg/TFMessage"
  gz_type_name: "gz.msgs.Pose_V"
  direction: GZ_TO_ROS

- ros_topic_name: "/tf"
  gz_topic_name: "/model/sphere/pose"
  ros_type_name: "tf2_msgs/msg/TFMessage"
  gz_type_name: "gz.msgs.Pose_V"
  direction: GZ_TO_ROS

Note

You will see that bridge files allow more flexibility. For instance, we are able to bridge topics in that have different names in Gazebo and ROS2.

We now have to call ros_gz_bridge using this newly created file. Note that some bash commands will not expand ~ into the home folder. We can replace those instances safely with $HOME. We send any configuration we want with the flag --ros-args -p, then set the parameter config_file to have a path to our newly created configuration file.

ros2 run ros_gz_bridge \
parameter_bridge \
--ros-args -p \
config_file:=$HOME/gazebo_tutorial_workspace/bridge_config/transforms.yaml

In the messages published to tf2 by gazebo, you will notice that the frame of reference is the name of the scene. In this case, shapes_with_tf2_publisher. Therefore, to see that the frames are correctly published via ROS2, we can see them in rviz2 with the following command.

ros2 run rviz2 rviz2 -f shapes_with_tf2_publisher

After adding the TF display, you’ll be able to see all the relevant frames.

Exercise

Suppose that you added a new model to shapes_with_tf2_publisher.sdf and you wanted to publish that information to /tf as well. What files would you modify and what steps would you take to make that possible?

So far, we have seen the basics of ros_gz_bridge, mostly allowing us to expose Gazebo information in ROS2. We haven’t used any of these in our own nodes, so we will do that in the following section.

Using ros_gz_bridge

Contents

Using ros_gz_bridge#

Sensors#

gz.msgs.Image#

gz.msgs.LaserScan#

Getting pose information#

Getting transforms#

Using `ros_gz_bridge`#