使用机器人操作系统ROS 2和仿真软件Gazebo 9环境综合测试教程（三）

在完成教程（一）搭建机器人和（二）命令遥控可视化后，将仿真机器人用于更为逼真的环境，可以测试如SLAM，区域覆盖以及场馆巡逻算法，这里环境均采用aws提供模型，分别为smallhouse和bookstore，环境适用于ROS2和ROS1全部案例，但ROS1内容不做讲解，这里只简要叙述一下ROS2中调试和使用的过程。

ROS2和Gazebo9中mobot室内环境仿真测试

在环境中添加机器人模型：

功能	ROS 1	ROS 2
Service names	`spawn_sdf_model`	`spawn_entity`
	`spawn_urdf_model`	`spawn_entity`
	`delete_model`	`delete_entity`
	`delete_light`	`delete_entity`

Service types	`gazebo_msgs/SpawnModel`	`gazebo_msgs/SpawnEntity`
	`gazebo_msgs/DeleteModel`	`gazebo_msgs/DeleteEntity`
	`gazebo_msgs/DeleteLight`	`gazebo_msgs/DeleteEntity`

Fields	`model_name`	`name` (optional)
	`light_name`	`name` (optional)
	`model_xml`	`xml`
	`robot_namespace` (optional)	`robot_namespace` (optional)
	`initial_pose` (optional)	`initial_pose` (optional)
	`reference_frame` (optional)	`reference_frame` (optional)

在launch中添加机器人需要注意如上差异，如添加一个urdf格式机器人可参考如下命令：

ros2 service call /spawn_entity 'gazebo_msgs/SpawnEntity' '{name: "urdf_ball", xml: "<?xml version=\"1.0\" ?><robot name=\"will_be_ignored\"><link name=\"link\"><visual><geometry><sphere radius=\"1.0\"/></geometry></visual><inertial><mass value=\"1\"/><inertia ixx=\"1\" ixy=\"0.0\" ixz=\"0.0\" iyy=\"1\" iyz=\"0.0\" izz=\"1\"/></inertial></link></robot>"}'

如果需要在制定位置插入机器人，需要查阅spawn_entity.py源码：

        # Encode xml object back into string for service call
        entity_xml = ElementTree.tostring(xml_parsed)

        # Form requested Pose from arguments
        initial_pose = Pose()
        initial_pose.position.x = float(self.args.x)
        initial_pose.position.y = float(self.args.y)
        initial_pose.position.z = float(self.args.z)

        q = quaternion_from_euler(self.args.R, self.args.P, self.args.Y)
        initial_pose.orientation.w = q[0]
        initial_pose.orientation.x = q[1]
        initial_pose.orientation.y = q[2]
        initial_pose.orientation.z = q[3]

注意这里的initial_pose和表中参数的对应情况，不再赘述。

mobot加入smallhouse场景如下所示，支持多机器人！后续补充：

可以在此环境中复习，前2课所学过的全部内容。

启动文件smallhouse.launch.py代码如下：

import os

from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.actions import ExecuteProcess, DeclareLaunchArgument
from launch.actions import IncludeLaunchDescription
from launch_ros.actions import Node
from launch.conditions import IfCondition
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch.substitutions import LaunchConfiguration

# this is the function launch  system will look for

def generate_launch_description():

    robot_name = 'mobot'
    world_file_name = 'smallhouse.world'

    # full  path to urdf and world file
    
    world = os.path.join(get_package_share_directory(robot_name), 'worlds', world_file_name)

    urdf = os.path.join(get_package_share_directory(robot_name), 'urdf', 'mobot.urdf')
    
    # read urdf contents because to spawn an entity in 
    # gazebo we need to provide entire urdf as string on  command line
    #small_house = launch.actions.IncludeLaunchDescription(
    #    launch.launch_description_sources.PythonLaunchDescriptionSource(
    #        os.path.join(
    #            get_package_share_directory('aws_robomaker_small_house_world'),
    #            'launch',
    #            'small_house.launch.py')))

    # Spawn mobot
    spawn_mobot = Node(
        package='gazebo_ros',
        node_executable='spawn_entity.py',
        node_name='spawn_entity',
        #node_namespace=namespace_,
        output='screen',
        #emulate_tty=True,
        arguments=['-entity',
                   'mobot',
                   '-x', '3.5', '-y', '1.0', '-z', '0.1',
                   '-file', urdf
                   ]
    )

    #xml = open(urdf, 'r').read()

    # double quotes need to be with escape sequence
    #xml = xml.replace('"', '\\"')

    # this is argument format for spwan_entity service 
    #spwan_args = '{name: \"mobot\", xml: \"'  +  xml + '\"}'

    # create and return launch description object
    return LaunchDescription([

        # start gazebo, notice we are using libgazebo_ros_factory.so instead of libgazebo_ros_init.so
        # That is because only libgazebo_ros_factory.so contains the service call to /spawn_entity
        ExecuteProcess(
            cmd=['gazebo', '--verbose', world, '-s', 'libgazebo_ros_factory.so'],
            output='screen'),
        
        # tell gazebo to spwan your robot in the world by calling service
        # ExecuteProcess(
        #    cmd=['ros2', 'service', 'call', '/spawn_entity', 'gazebo_msgs/SpawnEntity', spwan_args],
        #    output='screen'),
        #small_house,
        spawn_mobot,
        
    ])

机器人初始位置为x: 3.5 y: 1.0 z: 0.1，参考如下文档片段：

Robot Simulation - Initial Position

Do not use (0,0,0) for the initial position as it will collide with the lounge chairs. Instead, a resonable position is (3.5,1.0,0.0).

机器人可以加载已有的ROS2功能包，如导航功能包等。

具体参考：2020年ROS机器人操作系统用户官方调查文末的介绍。

关于环境综合测试更多截图如下所示：

smallhouse：