Hi

I'm trying to add a cube to my gazebo scene programmatically while gazebo is running.

I found that ignition has the service /world/my_world/create service that accepts new urdf/sdf files.

However, I'm struggling to send the correct request in python, since I don't know how to install the ignition messages on my system and how the request has to be structured.

Here is a tutorial in C++: https://gazebosim.org/api/gazebo/6.9/entity_creation.html

Here is the terminal call which spawns a sphere in the world:

ign service -s /world/empty/create \
--reqtype ignition.msgs.EntityFactory \
--reptype ignition.msgs.Boolean \
--timeout 300 \
--req 'sdf: '\
'"<?xml version=\"1.0\" ?>'\
'<sdf version=\"1.6\">'\
'<model name=\"spawned_model\">'\
'<link name=\"link\">'\
'<visual name=\"visual\">'\
'<geometry><sphere><radius>1.0</radius></sphere></geometry>'\
'</visual>'\
'<collision name=\"visual\">'\
'<geometry><sphere><radius>1.0</radius></sphere></geometry>'\
'</collision>'\
'</link>'\
'</model>'\
'</sdf>" '\
'pose: {position: {z: 10}} '\
'name: "new_name" '\
'allow_renaming: true'

My plan:

1. Install ignition messages (But how?)

2. Setup ign bridge to forward message /world/my_world/create from ign to ROS2 (in launch file)

   ros_ign_bridge (clock -> ROS 2)

   Node(
       package="ros_ign_bridge",
       executable="parameter_bridge",
       output="log",
       arguments=[
           "/world/my_world/create@ignition.msgs.EntityFactory@ignition.msgs.EntityFactory",
           "--ros-args",
           "--log-level",
           log_level,
       ],
       parameters=[{"use_sim_time": use_sim_time}],
   ),
   

3. Use python script to spawn cube.urdf in gazebo world

Importing the library:

from ignition-messages import EntityFactory # What is the correct syntax/name of the library?

Publishing the message: How do I construct a valid message?

my_sdf = """
            <?xml version="1.0" ?>
            <sdf version='1.7'>
            <model name='sphere'>
                <link name='link'>
                <pose>0 0 0.5 0 0 0</pose>
                <visual name='visual'>
                    <geometry><sphere><radius>1</radius></sphere></geometry>
                </visual>
                <collision name='collision'>
                    <geometry><sphere><radius>1</radius></sphere></geometry>
                </collision>
                </link>
            </model>
            </sdf>"""

            publisher = self.create_publisher(EntityFactory, '/world/my_world/create', 1)

            msg = EntityFactory()
            while rclpy.ok():
                msg.data = 'Hello World:  ' # How do I construct a valid message?
                msg.model = my_sdf
                publisher.publish(msg)

This is the message definition: https://github.com/gazebosim/gz-msgs/blob/ign-msgs8/proto/ignition/msgs/entity_factory.proto

Thanks in advance for your help.