博客

1. ros2中 launch文件是一个.py文件，而ros1中是一个 .launch文件。
2. 如何将urdf导入现有的工程
   
   背景：新建package，如何写urdf并在gazebo中显示？
   
   答：1. 新建urdf文件夹，在package的下一层目录，和src，include等文件夹在一层。并把urdf文件写出来或者粘过来。
   
   

2.改写cmakelist.txt文件

在

末尾

添加 include代码

作用：配置编译过程安装urdf、worlds和meshes目录到install文件夹中。

因为所有的软件包都将有ROS环境中的安装目录提供，所以在编译软件包时创建该目录。

install(DIRECTORY urdf
  DESTINATION share/${PROJECT_NAME})

3.编写launch文件

要在Gazebo中看到机器人，需要创建启动（launch）文件夹和启动文件

在启动文件中，将做两件事。

• 使用预定义的设置和启动Gazebo mobot_room.world
• 调用gazebo提供的spawn_entity服务以生成mobot.urdf在世界上定义的机器人。

import os
 
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.actions import ExecuteProcess, DeclareLaunchArgument
from launch_ros.actions import Node
from launch.substitutions import LaunchConfiguration
 
# this is the function launch  system will look for
 
def generate_launch_description():
 
    robot_name = 'autocar_test'
    #world_file_name = 'mobot_room.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', 'box.urdf')
    
    # read urdf contents because to spawn an entity in 
    # gazebo we need to provide entire urdf as string on  command line
 
    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: \"autocar_test\", 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', '-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'),
    ])

（该段代码参考张瑞雷老师博客

https://www.guyuehome.com/6788

https://zhangrelay.blog.csdn.net/article/details/104296249）

4. 再次改写cmakelist文件，实现编译后安装到启动文件夹

install(DIRECTORY launch
  DESTINATION share/${PROJECT_NAME})

5.编译等步骤

cd ~/dev_ws
colcon build
. install/setup.zsh 或者 source install/setup.zsh 
ros2 launch autocar_test box_launch.py

20201116更新

1. 当前遇到模型更新需要：关闭gazebo->重新启动launch.py->重启gazebo的问题
   
   解决方案：
   
   cd ~/dev_ws
   
   . install/setup.zsh 或者 source install/setup.zsh
   
   ros2 launch autocar_test box_launch.py
   
   不过，会报错：