（ros2）gazebo中显示机器人模型最小系统

<launch>
<group>
<let name="robot_description" value="$(command 'xacro $(find-pkg-share gazebo_pkg)/urdf/total.xacro')"/>
<include file="$(find-pkg-share ros_gz_sim)/launch/gz_sim.launch.py">
    <arg name="gz_args" value="-v 4 default.sdf"/>
</include>
<node pkg="ros_gz_sim" exec="create" args="-world default -file $(find-pkg-share gazebo_pkg)/urdf/total.urdf"> 
</node> 
</group>
</launch>

只需要urdf文件和sdf文件就可以了，不用每次把urdf转换为sdf