大家好，我是小鱼，上一节讲完joint和link，我们来把我们上面定义的简单的URDF(包含身体和雷达)用RVIZ2显示出来，直观的感受下，我们的机器人模型。

URDF可视化的步骤如下：

1. 建立机器人描述功能包

2. 建立urdf文件夹编写urdf文件

3. 建立launch文件夹，编写launch文件

4. 修改setup.py配置，编译测试

依赖

sudo apt install ros-$ROS_DISTRO-joint-state-publisher-gui ros-$ROS_DISTRO-robot-state-publisher

joint_state_publisher_gui，还有一个兄弟叫做joint_state_publisher两者区别在于joint_state_publisher_gui运行起来会跳出一个界面，通过界面可以操作URDF中能动的关节

建立功能包

轻车熟路，先创建一个chapt8_ws工作空间，然后建立功能包，包的类型选ament_python

mkdir -p chapt8_ws/src
cd chapt8_ws/src
ros2 pkg create fishbot_description --build-type ament_python

建立URDF文件

建立URDF文件夹，创建urdf文件

cd fishbot_description && mkdir urdf 
cd urdf && touch fishbot_base.urdf

完成后src下的目录结构：

编辑fishbot_base.urdf

<?xml version="1.0"?>
<robot name="fishbot">
    
  <!-- base link -->
  <link name="base_link">
      <visual>
      <origin xyz="0 0 0.0" rpy="0 0 0"/>
      <geometry>
        <cylinder length="0.12" radius="0.10"/>
      </geometry>
    </visual>
  </link>
    
  <!-- laser link -->
  <link name="laser_link">
      <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <cylinder length="0.02" radius="0.02"/>
      </geometry>
      <material name="black">
          <color rgba="0.0 0.0 0.0 0.8" /> 
      </material>
    </visual>
  </link>
    
  <!-- laser joint -->
    <joint name="laser_joint" type="fixed">
        <parent link="base_link" />
        <child link="laser_link" />
        <origin xyz="0 0 0.075" />
    </joint>

</robot>

建立launch文件

在目录src/fishbot_description下创建launch文件夹并在其下新建display_rviz2.launch.py文件。

mkdir launch
touch display_rviz2.launch.py

完成后的目录结构：

在launch中添加

import os
from launch import LaunchDescription
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node
from launch_ros.substitutions import FindPackageShare


def generate_launch_description():
    package_name = 'fishbot_description'
    urdf_name = "fishbot_base.urdf"

    ld = LaunchDescription()
    pkg_share = FindPackageShare(package=package_name).find(package_name) 
    urdf_model_path = os.path.join(pkg_share, f'urdf/{urdf_name}')

    robot_state_publisher_node = Node(
        package='robot_state_publisher',
        executable='robot_state_publisher',
        arguments=[urdf_model_path]
        )

    joint_state_publisher_node = Node(
        package='joint_state_publisher_gui',
        executable='joint_state_publisher_gui',
        name='joint_state_publisher_gui',
        arguments=[urdf_model_path]
        )

    rviz2_node = Node(
        package='rviz2',
        executable='rviz2',
        name='rviz2',
        output='screen',
        )

    ld.add_action(robot_state_publisher_node)
    ld.add_action(joint_state_publisher_node)
    ld.add_action(rviz2_node)

    return ld

想要可视化模型需要三个节点参与

• joint_state_publisher_gui 负责发布机器人关节数据信息，通过joint_states话题发布

• robot_state_publisher_node负责发布机器人模型信息robot_description，并将joint_states数据转换tf信息发布

• rviz2_node负责显示机器人的信息

修改setup.py

导入头文件

from glob import glob
import os

加入目录安装

('share/ament_index/resource_index/packages',
['resource/' + package_name]),
('share/' + package_name, ['package.xml']),

完整

from setuptools import setup
from glob import glob
import os

package_name = 'fishbot_description'

setup(
    name=package_name,
    version='0.0.0',
    packages=[package_name],
    data_files=[
        ('share/ament_index/resource_index/packages',
            ['resource/' + package_name]),
        ('share/' + package_name, ['package.xml']),
        (os.path.join('share', package_name, 'launch'), glob('launch/*.launch.py')),
        (os.path.join('share', package_name, 'urdf'), glob('urdf/**')),
    ],
    install_requires=['setuptools'],
    zip_safe=True,
    maintainer='root',
    maintainer_email='root@todo.todo',
    description='TODO: Package description',
    license='TODO: License declaration',
    tests_require=['pytest'],
    entry_points={
        'console_scripts': [
        ],
    },
)

编译测试

编译

colcon build --packages-select fishbot_description

运行测试

source install/setup.bash
ros2 launch fishbot_description display_rviz2.launch.py

添加robotmodel模块，分别选择link名称如下，即可看到机器人的模型显示

这里大家可以参考图理一理launch文件中启动的三个节点的关系。

然后打开TF模块，看一下机器人的坐标系关系

练习

练习1：尝试将修改机器人身体颜色为蓝色，透明度为50%(0.1 0.1 1.0 0.5)

练习2：尝试在URDF中添加imu_link并使用imu_joint将其固定在车体的中心上方2cm，imu采用的几何形状为box。长宽高均为2cm

<link name="base_link">
    <visual>
        <origin xyz="0 0 0.0" rpy="0 0 0"/>
    <geometry>
        <cylinder length="0.12" radius="0.10"/>
    </geometry>
    <material name="blue">
        <color rgba="0.1 0.1 1.0 0.5" /> 
    </material>
    </visual>
</link>

<link name="imu_link">
    <visual>
    <origin xyz="0 0 0.0" rpy="0 0 0"/>
    <geometry>
          <box size="0.02 0.02 0.02"/>
    </geometry>
  </visual>
</link>

<!-- imu joint -->
<joint name="imu_joint" type="fixed">
    <parent link="base_link" />
    <child link="imu_link" />
    <origin xyz="0 0 0.02" />
</joint>