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1 ROS工程结构

1.1 catkin工作空间

Catkin工作空间是创建、修改、编译catkin软件包的目录。catkin的工作空间，直观的形容就是一个仓库，里面装载着ROS的各种项目工程，便于系统组织管理调用。

创建工作空间：

mkdir -p ~/catkin_ws/src  # 创建文件夹
cd ~/catkin_ws/src        # 进入文件夹
catkin_init_workspace     # 把当前目录初始化为一个ROS工作空间
cd ..                     # 返回上级目录
catkin_make               # 构建工作区中的代码。

catkin的结构十分清晰，它包括了src、build、devel三个路径，在有些编译选项下也可能包括其他。但这三个文件夹是catkin编译系统默认的。它们的具体作用如下：

src/: ROS的catkin软件包（源代码包）

build/: catkin（CMake）的缓存信息和中间文件

devel/: 生成的目标文件（包括头文件，动态链接库，静态链接库，可执行文件等）、环境变量

一个简单的工作空间如下所示：

1 ROS project structure

1.1 catkin workspace

Catkin workspace is the directory where catkin software packages are created, modified, and compiled. Catkin's workspace can be intuitively described as a warehouse, which contains various ROS project projects to facilitate system organization, management and calling.

Create workspace:

mkdir -p ~/catkin_ws/src  # Create a folder
cd ~/catkin_ws/src        # Enter the folder
catkin_init_workspace     # Initialize the current directory into a ROS workspace
cd ..                     # Return to the parent directory
catkin_make               # Build the code in the workspace

The structure of catkin is very clear. It includes three paths: src, build, and devel. It may also include others under some compilation options. But these three folders are the default for the catkin compilation system. Their specific functions are as follows:

src/: ROS catkin software package (source code package)

build/: cache information and intermediate files of catkin (CMake)

devel/: Generated target files (including header files, dynamic link libraries, static link libraries, executable files, etc.), environment variables

A simple workspace looks like this:

workspace_folder/        -- WORKSPACE
  src/                   -- SOURCE SPACE
    CMakeLists.txt       -- 'Toplevel' CMake file, provided by catkin
    package_1/
      CMakeLists.txt     -- CMakeLists.txt file for package_1
      package.xml        -- Package manifest for package_1
    ...
    package_n/
      CMakeLists.txt     -- CMakeLists.txt file for package_n
      package.xml        -- Package manifest for package_n

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1.2 ROS软件包

Package不仅是Linux上的软件包，也是catkin编译得基本单元，我们使用 catkin_make 编译的对象就是每个ROS的package。

+-- PACKAGE
    +-- CMakeLists.txt 
    +-- package.xml 
    +-- src/
    +-- include/ 
    +-- scripts/
    +-- msg/ 
    +-- srv/ 
    +-- urdf/
    +-- launch/

CMakeLists.txt: 定义package的包名、依赖、源文件、目标文件等编译规则，是package不可少的成分
package.xml: 描述package的包名、版本号、作者、依赖等信息，是package不可少的成分
src/: 存放ROS的源代码，包括C++的源码和(.cpp)以及Python的module(.py)
include/: 存放C++源码对应的头文件
scripts/: 存放可执行脚本，例如shell脚本(.sh)、Python脚本(.py)
msg/: 存放自定义格式的消息(.msg)
srv/: 存放自定义格式的服务(.srv)
urdf/: 存放机器人的模型描述(.urdf或.xacro)、3D模型文件(.sda, .stl, .dae等)
launch/: 存放launch文件(.launch或.xml)

创建自己的软件包:

指令格式：

catkin_create_pkg命令会要求你输入package_name，如有需要还可以在后面添加一些需要依赖的其它软件包：

1.2 ROS software package

Package is not only a software package on Linux, but also the basic unit of catkin compilation. The object we use catkin_make to compile is each ROS package.

+--PACKAGE
     +-- CMakeLists.txt 
     +-- package.xml 
     +-- src/ 
     +-- include/ 
     +-- scripts/
     +-- msg/ 
     +-- srv/ 
     +-- urdf/
     +-- launch/

CMakeLists.txt: Defines the package name, dependencies, source files, target files and other compilation rules of the package. It is an essential component of the package.
package.xml: Describes the package name, version number, author, dependencies and other information of the package, which is an indispensable component of the package.
src/: stores ROS source code, including C++ source code (.cpp) and Python module (.py)
include/: stores the header files corresponding to the C++ source code
scripts/: stores executable scripts, such as shell scripts (.sh), Python scripts (.py)
msg/: stores messages in custom format (.msg)
srv/: stores services in custom formats (.srv)
urdf/: stores the robot’s model description (.urdf or .xacro) and 3D model files (.sda, .stl, .dae, etc.)
launch/: stores launch files (.launch or .xml)

Create your own package:

Command format:

The catkin_create_pkg command will ask you to enter package_name. If necessary, you can also add some other dependent software packages later:

catkin_create_pkg <package_name> [depend1] [depend2] [depend3]

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- 例如：

For example:

5673ade8eb00a28794557125b7d1c8cd332434a9

catkin_create_pkg beginner_tutorials std_msgs rospy roscpp

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2 ROS通信架构

2.1 Master与node

1 Master

节点管理器，每个node启动前要向master注册，管理node之间的通信。

2 roscore

启动master，也会启动rosout（日志管理）和parameter server（参数管理器）

3 node

ROS的进程、pkg里可执行文件运行的实例。

$rosrun [pkg_name] [node_name] #启动
$rosnode list  #列出当前运行的node信息
$rosnode info [node_name] #显示某个node的详细信息
$rosnode kill [node_name] #结束某个node
=======
# 2 ROS communication architecture

<img src = ../../resources/11-ApplicationBaseROS/11.1.2-1.png
width="500" align="center">

## 2.1 Master and node

### 1 Master

Node manager. Each node must register with the master before starting and manage the communication between nodes.

### 2 roscore

Starting the master will also start rosout (log management) and parameter server (parameter manager)

### 3 nodes

ROS processes and instances of running executable files in pkg.

```bash
$rosrun [pkg_name] [node_name] #Start
$rosnode list #List currently running node information
$rosnode info [node_name] #Display detailed information of a node
$rosnode kill [node_name] #End a node
>>>>>>> 5673ade8eb00a28794557125b7d1c8cd332434a9

4 launch

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启动master和多个node。

Start the master and multiple nodes.

$roslaunch [pkg_name] [file_name.launch]

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2.2 Service 与 Topic

我们提供一些 service 和 topic，用以和 mycobot 交互。

1 Service

命令行中输入:

# 显示活动的服务信息
rosservice list

命令	详细说明
rosservice list	显示活动的服务信息
rosservice info [服务名称]	显示指定服务的信息
rosservice type [服务名称]	显示服务类型
rosservice find [服务类型]	查找指定服务类型的服务
rosservice uri [服务名称]	显示ROSRPC URI服务
rosservice args [服务名称]	显示服务参数
rosservice call [服务名称] [参数]	用输入的参数请求服务

2 Topic

命令行中输入

# 显示活动的服务信息
rostopic list

命令	详细说明
rostopic list	显示活动的话题目录
rostopic echo [话题名称]	实时显示指定话题的消息内容
rostopic find [类型名称]	显示使用指定类型的消息的话题
rostopic type [话题名称]	显示指定话题的消息类型
rostopic bw [话题名称]	显示指定话题的消息带宽（bandwidth）
rostopic hz [话题名称]	显示指定话题的消息数据发布周期
rostopic info [话题名称]	显示指定话题的信息
rostopic pub [话题名称] [消息类型] [参数]	用指定的话题名称发布消息

	service	topic
同步性	异步	同步
通信模型	发布/订阅	服务器/客户端
底层协议	ROSTCP/ROSUDP	ROSTCP/ROSUDP
反馈机制	无	有
缓冲区	有	无
实时性	弱	强
节点关系	多对多	一对多
适用场景	数据传输	逻辑处理

2.3 msg和srv简介

msg：msg文件是描述ROS消息字段的简单文本文件。它们用于为不同语言（c++或者python等）的消息生成源代码。
srv：srv文件用来描述服务。它由两部分组成：请求（request）和响应（response）。 msg文件存储在包的msg目录中，而srv文件存储在srv目录中。

1 rosmsg

rosmsg是用于显示有关 ROS消息类型的信息的命令行工具。

rosmsg 演示：

rosmsg show       # 显示消息描述
rosmsg info       # 显示消息信息
rosmsg list       # 列出所有消息
rosmsg md5        # 显示 md5 加密后的消息
rosmsg package    # 显示某个功能包下的所有消息
rosmsg packages   # 列出包含消息的功能包

rosmsg list 会列出当前 ROS 中的所有 msg
rosmsg packages 列出包含消息的所有包
rosmsg package 列出某个包下的所有msg

//rosmsg package  # 包名 
=======
## 2.2 Service and Topic

We provide some services and topics for interacting with mycobot.

### 1 Service

**Enter in the command line:**

Related commands and instructions:

|command    |Detailed description|
|--|--|
|rosservice list    |Display active service information|
|rosservice info [service name] |    Display information about the specified service|
|rosservice type [service name] |    Show service type|
|rosservice find [service name] |    Find a service for a specified service type|
|rosservice uri [service name]     |show ROSRPC URI service|
|rosservice args [service name] |    show service parameters|
|rosservice call [service name] [parameters]    |Request service with input parameters|

### 2 Topic

**Enter in the command line:**

Related commands and instructions:

|Command    |Detailed description|
|--|--|
|rostopic list     | Display active topic list
|rostopic echo [topic name] | Display the message content of the specified topic in real time
|rostopic find [type name] |    Display threads with messages of the specified type 
|rostopic type [topic name]    | Displays the message type of the specified topic 
|rostopic bw [topic name]      | Display the message bandwidth of the specified topic（bandwidth） 
|rostopic hz [topic name]   |    Display the message data publishing cycle of the specified topic
|rostopic info [topic name |    Display information about the specified topic 
|rostopic pub [topic name] [message type] [parameters]    | Post a message with the specified topic name

**The difference between service and topic:**

|  |service|topic|
|--|--|--|
|Synchronization|Asynchronous|Synchronous|
|communication model|pub/sub|server/client|
|underlying protocol|ROSTCP/ROSUDP|ROSTCP/ROSUDP|
|Feedback Mechanism|No|Yes|
|buffer|Yes|No|
|Real-time|Weak|Strong|
|Node Relationship|Many-to-Many|One-to-Many|
|Applicable Scenarios|Data Transmission|Logical Processing|

you can go to[service](http://wiki.ros.org/rosservice) and [topic](http://wiki.ros.org/rostopic) learn more about the use of these two features

## 2.3 Introduction to msg and srv

* msg：The msg file is a simple text file describing the fields of a ROS message. They are used to generate source code for messages in different languages (c++ or python, etc.).
* srv：srv files are used to describe services. It consists of two parts: the request (request) and the response (response).
msg files are stored in the msg directory of the package, and srv files are stored in the srv directory.

### 1 rosmsg

rosmsg is a command line tool for displaying information about ROS message types.

**rosmsg demo:**

```bash
rosmsg show       # Show message description
rosmsg info       # Display message information
rosmsg list       # list all messages
rosmsg md5        # Display md5 encrypted message
rosmsg package    # Display all messages under a feature pack
rosmsg packages   # List feature packs that contain messages

rosmsg list will list all msgs in the current ROS
rosmsg packages List all packages containing messages
rosmsg package List all msgs under a package

//rosmsg package  # Package names
>>>>>>> 5673ade8eb00a28794557125b7d1c8cd332434a9
rosmsg package turtlesim

rosmsg show <<<<<<< HEAD 显示消息描述

//rosmsg show # 消息名称
rosmsg show turtlesim/Pose
# 结果:
=======
Show message description

```bash
//rosmsg show # message name
rosmsg show turtlesim/Pose
# result:
>>>>>>> 5673ade8eb00a28794557125b7d1c8cd332434a9
float32 x
float32 y
float32 theta
float32 linear_velocity
float32 angular_velocity

rosmsg info <<<<<<< HEAD 作用与 rosmsg show 一样
rosmsg md5 一种校验算法，保证数据传输的一致性

2 rossrv

rossrv是用于显示有关ROS服务类型的信息的命令行工具，与 rosmsg 使用语法高度雷同。

rossrv show       # 显示服务消息详情
rossrv info       # 显示服务消息相关信息
rossrv list       # 列出所有服务信息
rossrv md5        # 显示 md5 加密后的服务消息
rossrv package    # 显示某个包下所有服务消息
rossrv packages   # 显示包含服务消息的所有包

rossrv list 会列出当前 ROS 中的所有 srv 消息
rossrv packages 列出包含服务消息的所有包
rossrv package 列出某个包下的所有msg

//rossrv package # 包名 
=======
Works the same as rosmsg show

* rosmsg [md5](http://wiki.ros.org/ROS/Technical%20Overview#Message_serialization_and_msg_MD5_sums) 
A check algorithm to ensure the consistency of data transmission

### 2 rossrv

rossrv is a command-line tool for displaying information about ROS service types, and uses a syntax that is highly similar to rosmsg.

```bash
rossrv show       # Display service message details
rossrv info       # Display information about service messages
rossrv list       # List all service information
rossrv md5        # Display md5 encrypted service messages
rossrv package    # Display all service messages under a package
rossrv packages   # Show all packages that contain service messages

rossrv list Will list all srv messages in the current ROS
rossrv packages List all packages that contain service messages
rossrv package List all msgs under a package

//rossrv package # Package names
>>>>>>> 5673ade8eb00a28794557125b7d1c8cd332434a9
rossrv package turtlesim

rossrv show <<<<<<< HEAD 显示消息描述

//rossrv show # 消息名称
rossrv show turtlesim/Spawn
# 结果:
=======
Show message description

```bash
//rossrv show # message name
rossrv show turtlesim/Spawn
# result:
>>>>>>> 5673ade8eb00a28794557125b7d1c8cd332434a9
float32 x
float32 y
float32 theta
string name
---
string name

rossrv info <<<<<<< HEAD 作用与 rossrv show 一致
rossrv md5 对 service 数据使用 md5 校验(加密)

3 URDF介绍

Unified Robot Description Format，统一机器人描述格式，简称为URDF。ROS中的urdf功能包包含一个URDF的C++解析器，URDF文件使用XML格式描述机器人模型。
URDF 不能单独使用，需要结合 Rviz 或 Gazebo，URDF 只是一个文件，需要在 Rviz 或 Gazebo 中渲染成图形化的机器人模型。

3.1 urdf文件描述

代码示例：

本处只截取部分代码进行展示：

The effect is the same as rossrv show

rossrv md5 Use md5 checksum (encryption) for service data

3 Introduction to URDF

Unified Robot Description Format，Unified Robot Description Format, abbreviated as URDF. The urdf package in ROS contains a C++ parser for URDF, and URDF files describe robot models in XML format. *URDF cannot be used alone, it needs to be combined with Rviz or Gazebo. URDF is just a file that needs to be rendered into a graphical robot model in Rviz or Gazebo.

3.1 urdf file description

Code example:

Only part of the code is intercepted here for display:

<?xml version="1.0"?>
<robot  xmlns:xacro="http://www.ros.org/wiki/xacro" name="firefighter" >

<xacro:property name="width" value=".2" />

  <!-- base -->
  <link name="base">
    <visual>
      <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/base.dae"/>
      </geometry>
      <origin xyz = "0 0 0 " rpy = " 0 0 0"/>
    </visual>
    <collision>
      <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/base.dae"/>
        </geometry>
        <origin xyz = "0 0 0 " rpy = " 0 0 0"/>
    </collision>
  </link>

  <!-- body -->
  <link name="link_body">
    <visual>
      <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/body.dae"/>
      </geometry>
      <origin xyz = "0 0 -0.11 " rpy = " 0 0 0"/>
    </visual>
    <collision>
     <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/body.dae"/>
      </geometry>
      <origin xyz = "0 0 -0.11 " rpy = " 0 0 0"/>
    </collision>
  </link>

  <!-- screen head -->
  <link name="link_head">
    <visual>
      <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/head.dae"/>
      </geometry>
      <origin xyz = "0 0 -0.1 " rpy = " 0 0 0"/>
    </visual>
    <collision>
     <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/head.dae"/>
      </geometry>
      <origin xyz = "0 0 -0.1 " rpy = " 0 0 0"/>
    </collision>
  </link>

  <!-- camera -->
  <link name="link_eye">
    <visual>
      <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/head_eye.dae"/>
      </geometry>
      <origin xyz = "0 0 -0.0 " rpy = " 0 0 -0.6981"/>
    </visual>
    <collision>
     <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/head_eye.dae"/>
      </geometry>
      <origin xyz = "0 0 -0.1 " rpy = " 0 0 -0.6981"/>
    </collision>
  </link>

  <link name="link1_L">
    <visual>
      <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/joint1_L.dae"/>
      </geometry>
      <origin xyz = "0 0 -0.084 " rpy = " 0 0 0"/>
    </visual>
    <collision>
     <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/joint1_L.dae"/>
      </geometry>
      <origin xyz = "0 0 -0.084 " rpy = " 0 0 0"/>
    </collision>
  </link>

  <link name="link2_L">
    <visual>
      <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/joint2_L.dae"/>
      </geometry>
      <origin xyz = "0 0 0.0 " rpy = " 3.14159 0 -1.5708"/>
    </visual>
    <collision>
     <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/joint2_L.dae"/>
      </geometry>
      <origin xyz = "0 0 0.0 " rpy = " 3.14159 0 -1.5708"/>
    </collision>
  </link>

  <link name="link3_L">
    <visual>
      <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/joint3_L.dae"/>
      </geometry>
      <origin xyz = "0 0 0.038 " rpy = " 0 0 0"/>
    </visual>
    <collision>
     <geometry>
       <mesh filename="package://mercury_description/urdf/mercury_b1/joint3_L.dae"/>
      </geometry>
      <origin xyz = "0 0 0.038 " rpy = " 0 0 0"/>
    </collision>
  </link>

  ......

  <joint name="eye" type="revolute">
    <axis xyz=" 0 0 1"/>
    <limit effort = "1000.0" lower = "0" upper = "0.83" velocity = "0"/>
    <parent link="link_head"/>
    <child link="link_eye"/>
    <origin xyz= " 0.03 0 -0.08   " rpy = "1.5708 0 0"/>  
  </joint>

  <joint name="head" type="revolute">
    <axis xyz=" 0 0 1"/>
    <limit effort = "1000.0" lower = "-2.4085" upper = "3.2812" velocity = "0"/>
    <parent link="link_body"/>
    <child link="link_head"/>
    <origin xyz= " 0 0 0.22   " rpy = "0 0 0"/>  
  </joint>

  <joint name="body" type="revolute">
    <axis xyz=" 0 0 1"/>
    <limit effort = "1000.0" lower = "-2.0594" upper = "2.0594" velocity = "0"/>
    <parent link="base"/>
    <child link="link_body"/>
    <origin xyz= " 0 0 0.231   " rpy = "0 0 0"/>  

    <joint name="joint1_L" type="revolute">
    <axis xyz=" 0 0 1"/>
    <limit effort = "1000.0" lower = "-3.1066" upper = "3.1066" velocity = "0"/>
    <parent link="link_body"/>
    <child link="link1_L"/>
    <origin xyz= " 0.075 0.186 0.085   " rpy = "-1.5708 0 -0.5235"/>  
  </joint>

  <joint name="joint2_L" type="revolute">
    <axis xyz=" 0 0 1"/>
    <limit effort = "1000.0" lower = "-1.4311" upper = "2.2689" velocity = "0"/>
    <parent link="link1_L"/>
    <child link="link2_L"/>
    <origin xyz= " 0 0 0  " rpy = "-1.5708 0 0"/>  
  </joint>

  <joint name="joint3_L" type="revolute">
    <axis xyz=" 0 0 1"/>
    <limit effort = "1000.0" lower = "-3.1066" upper = "3.1066" velocity = "0"/>
    <parent link="link2_L"/>
    <child link="link3_L"/>
    <origin xyz= " 0 -0.11 0  " rpy = "1.5708 0 0"/>  
  </joint>
  </joint>

</robot>

<<<<<<< HEAD

可以看出，urdf文件并不复杂，主要是由link和joint两个部分不断重复而成。

3.2 link部分

link元素描述具有惯性、可视特征和碰撞属性的刚体

3.2.1 属性

name： 用来描述链接本身的名称

3.2.2 元素

<inertial> (可选)
- 连杆的惯性特性
- <origin> (可选，defaults to identity if not specified)
  - 定义相对于连杆坐标系的惯性参考系的参考坐标，该坐标必需定义在连杆重心处，其坐标轴可与惯性主轴不平行。
  - xyz (可选，默认为零向量) 表示 x , y , z x,y,zx,y,z 方向的偏置，单位为米。
  - rpy(可选: defaults to identity if not specified) 表示坐标轴在RPY方向上的旋转，单位为弧度。
- <mass> 连杆的质量属性
- <inertia> 3×3旋转惯性矩阵，由六个独立的量组成：ixx, ixy, ixz, iyy, iyz, izz。
<visual> (可选)
- 连杆的可视化属性。用于指定连杆显示的形状（矩形、圆柱体等），同一连杆可以存在多个visual元素，连杆的形状为多个元素两个形成。一般情况下模型较为复杂可以通过soildwork绘制后生成stl调用，简单的形状如添加末端执行器等可以直接编写。同时可以在此处可根据理论模型和实际模型差距调整几何形状的位置。
- <namel> (可选) 连杆几何形状的名字。
- <origin> (可选，defaults to identity if not specified)
  - 相对于连杆的坐标系的几何形状坐标系。
  - xyz (optional: defaults to zero vector) 表示x , y , z x,y,zx,y,z 方向的偏置，单位为米。
  - rpy (optional: defaults to identity if not specified) 表示坐标轴在RPY方向上的旋转，单位为弧度。

<geometry> （必需）
- 可视化对象的形状，可以是下面的其中一种：
- <box> 矩形，元素包含长、宽、高。原点在中心。
- <cylinder> 圆柱体，元素包含半径、长度。原点中心。
- <sphere> 球体，元素包含半径。原点在中心。
- <mesh> 网格，由文件决定，同时提供 scale ，用于界定其边界。推荐使用 Collada .dae 文件，也支持.stl文件，但必须为一个本地文件。
<material> (可选)
- 可视化组件的材料。可以在link标签外定义，但必需在robot标签内，在link标签外定义时，需引用link的名字。
- <color>(可选) 颜色，由 red/green/blue/alpha 组成，大小范围在 [0,1] 内。
- <texture>(可选) 材料属性，由文件定义。

<collision> (可选)
- 连杆的碰撞属性。碰撞属性和连杆的可视化属性不同，简单的碰撞模型经常用来简化计算。同一个连杆可以有多个碰撞属性标签，连杆的碰撞属性表示由其定义的几何图形集构成。
- <name> (可选) 指定连杆几何形状的名称
- <origin> (可选，defaults to identity if not specified)
  - 碰撞组件的参考坐标系相对于连杆坐标系的参考坐标系。
  - xyz (可选，默认零向量) 表示x , y , z x,y,zx,y,z 方向的偏置，单位为米。
  - rpy (可选， defaults to identity if not specified) 表示坐标轴在RPY方向上的旋转，单位为弧度。
- <geometry> 与上述geometry元素描述相同

详细元素以及各个元素的作用可以前往官方文档进行查看

3.3 joint部分

joint部分描述了关节的运动学和动力学，并指定了关节的安全限值。

3.3.1 joint的属性：

name：

指定关节的唯一名称

type：

指定关节的类型，其中类型可以是下列类型之一：

revolute - 沿轴线旋转的铰链接头，其范围由上限和下限指定。
连续 - 一种连续铰链接头，围绕轴旋转，没有上限和下限。
棱柱形 - 沿轴滑动的滑动接头，其范围由上限和下限指定。
固定 - 这不是真正的关节，因为它不能移动。所有自由度都被锁定。这种类型的接头不需要轴，校准，动力学，极限或safety_controller。
浮动 - 此接头允许所有 6 个自由度的运动。
平面 - 此接头允许在垂直于轴的平面上运动。

3.3.2 joint的元素

<origin> (可选，defaults to identity if not specified) 从parent link到child link的变换，joint位于child link的原点，修改该参数可以调整连杆的位置，可用在调整实际模型与理论模型误差，但不建议大幅度修改，因为该参数影响连杆stl的位置，容易影响碰撞检测效果。
- xyz (可选: 默认为零向量) 代表x , y , z x,y,zx,y,z轴方向上的偏移，单位米。
- rpy (可选: 默认为零向量) 代表绕着固定轴旋转的角度：roll绕着x轴,pitch绕着y轴，yaw绕着z轴，用弧度表示。
<parent> (必需)
- parent link的名字是一个强制的属性。
- link parent link的名字，是这个link在机器人结构树中的名字。
<child> (必需)
- child link的名字是一个强制的属性。
- link child link的名字，是这个link在机器人结构树中的名字。

<axis>(可选: 默认为(1,0,0))
- joint的axis轴在joint的坐标系中。这是旋转轴(revolute joint)，prismatic joint移动的轴，是planar joint的标准平面。这个轴在joint坐标系中被指定。修改该参数可以调整关节的旋转所绕着的轴，常用于调整旋转方向，若模型旋向与实际相反，只需乘-1即可。固定(fixed)和浮动(floating)类型的joint不需要用到这个元素。
- xyz(必需) 代表轴向量的x , y , z x,y,zx,y,z分量，为标准化的向量。
<calibration> (可选)
- joint的参考点，用来矫正joint的绝对位置。
- rising (可选) 当joint正向运动时，参考点会触发一个上升沿。
- falling (可选) 当joint正向运动时，参考点会触发一个下降沿。
<dynamics>(可选)
- 该元素用来指定joint的物理性能。它的值被用来描述joint的建模性能，尤其是在仿真的时候。

<limit> (当关节为旋转或移动关节时为必需)

该元素为关节运动学约束。
lower (可选, 默认为0) 指定joint运动范围下界的属性(revolute joint的单位为弧度，prismatic joint的单位为米)，连续型的joint忽略该属性。
upper (可选, 默认为0) 指定joint运动范围上界的属性(revolute joint的单位为弧度，prismatic joint的单位为米)，连续型的joint忽略该属性。
effort (必需) 该属性指定了joint运行时的最大的力。
velocity (required) 该属性指定了joint运行时的最大的速度。

<mimic>(可选)

这个标签用于指定已定义的 joint 来模仿已存在的 joint 。这个joint的值可以用以下公式计算： value = multiplier * other_joint_value + offset
joint(必填) 需要模仿的joint的名字。
multiplier(可选) 指定上述公式中的乘数因子。
offset(可选) 指定上述公式中的偏移项。默认值为0

<safety_controller> (可选)

该元素为安全控制限制，此元素下数据会读入到move_group中，但实际上时无效，move_group会跳过此处限制直接读取limit下的参数内容，同时设置该元素有几率会导致规划失败。
soft_lower_limit (可选, 默认为0) 该属性指定了joint安全控制边界的下界，是joint安全控制的起始限制点。这个值需要大于上述的limit中的lower值。
soft_upper_limit (可选, 默认为0) 该属性指定了joint安全控制边界的上界，是joint安全控制的起始限制点。这个值需要小于上述的limit中的upper值。
k_position(可选, 默认为0) 本属性用于说明位置和速度之间的关系。
k_velocity(必需)
本属性用于说明力和速度之间的关系。
```

It can be seen that the urdf file is not complicated, it is mainly composed of two parts, link and joint, which are repeated continuously.

3.2 link section

The link element describes a rigid body with inertial, visual features, and collision properties

3.2.1 Attributes

name： The name used to describe the link itself

3.2.2 element

<inertial> (optional)
- Inertia properties of connecting rods
- <origin> (optional，defaults to identity if not specified)
  - Defines the reference coordinate of the inertial reference system relative to the connecting rod coordinate system. The coordinate must be defined at the center of gravity of the connecting rod, and its coordinate axis may not be parallel to the main axis of inertia.
  - xyz (optional, defaults to zero vector) Represents the offset in the x , y , z x,y,zx,y,z directions, in meters.
  - rpy(optional: defaults to identity if not specified) Indicates the rotation of the coordinate axis in the RPY direction, in radians.
- <mass> Mass properties of connecting rods
- <inertia> 3×3 rotational inertia matrix, consisting of six independent quantities: ixx, ixy, ixz, iyy, iyz, izz。
<visual> (optional)
- Visual properties of the connecting rod. It is used to specify the shape of the link display (rectangle, cylinder, etc.). There can be multiple visual elements in the same link, and the shape of the link is formed by two elements. In general, the model is more complex and can be drawn through soildwork to generate stl calls, and simple shapes such as adding end effectors can be directly written. At the same time, the position of the geometry can be adjusted according to the gap between the theoretical model and the actual model.
- <namel> (optional) The name of the connecting rod geometry.
- <origin> (optional，defaults to identity if not specified)
  - The geometry coordinate system relative to the coordinate system of the connecting rod.
  - xyz (optional: defaults to zero vector) Represents the offset in the x , y , z x,y,zx,y,z directions, in meters.
  - rpy (optional: defaults to identity if not specified) Indicates the rotation of the coordinate axis in the RPY direction, in radians.

<geometry> （required）
- The shape of the visualization, which can be one of the following:
- <box> A rectangle with elements including length, width, and height. The origin is in the center.
- <cylinder> Cylinder, elements include radius and length. center of origin.
- <sphere> Sphere, element containing the radius. The origin is in the center.
- <mesh> The grid, as determined by the file, also provides a scale to define its boundaries. Collada .dae files are recommended, .stl files are also supported, but must be a local file.
<material> (optional)
- Visualize the component's material. It can be defined outside the link tag, but it must be inside the robot tag. When defining outside the link tag, the name of the link must be quoted.
- <color>(optional) Color, consisting of red/green/blue/alpha, in the range [0,1].
- <texture>(optional) Material properties, defined by the file.

<collision> (optional)
- Collision properties of the link. Collision properties differ from visual properties of connecting rods, and simple collision models are often used to simplify calculations. The same link can have multiple collision attribute labels, and the collision attribute representation of the link is composed of the set of geometric shapes defined by it.
- <name> (optional) Specifies the name of the connecting rod geometry
- <origin> (optional，defaults to identity if not specified)
  - The reference coordinate system of the collision component is relative to the reference coordinate system of the link coordinate system.
  - xyz (optional, default zero vector) Represents the offset in the x , y , z x,y,zx,y,z directions, in meters.
  - rpy (optional, defaults to identity if not specified) Indicates the rotation of the coordinate axis in the RPY direction, in radians.
- <geometry> Same as the geometry element description above

Detailed elements and the role of each element can go to official documentation to view

3.3 joint part

The joint section describes the kinematics and dynamics of the joint and specifies safety limits for the joint.

3.3.1 properties of joint:

name：

Specifies a unique name for the joint

type：

Specifies the type of joint, where type can be one of the following:

revolute - A hinged joint that rotates along an axis, the range of which is specified by the upper and lower bounds.
Continuous - A continuous hinged joint that rotates around an axis with no upper and lower bounds.
Prismatic - A sliding joint that slides along an axis, the range of which is specified by upper and lower limits. +Fixed - this is not really a joint because it cannot move. All degrees of freedom are locked. This type of joint does not require axes, calibration, dynamics, limits or safety_controller。
Floating - This joint allows motion in all 6 degrees of freedom.
Plane - This joint allows movement in a plane perpendicular to the axis.

3.3.2 elements of joint

<origin> (optional，defaults to identity if not specified) In the transformation from parent link to child link, the joint is located at the origin of the child link. Modifying this parameter can adjust the position of the connecting rod. It can be used to adjust the error between the actual model and the theoretical model, but it is not recommended to modify it greatly, because this parameter affects the connecting rod stl The position of , easily affects the collision detection effect.
- xyz (optional: default to zero vector) Represents the offset in the x , y , z x,y,zx,y,z axis directions, in meters.
- rpy (optional: default to zero vector) Represents the angle of rotation around a fixed axis: roll is around the x-axis, pitch is around the y-axis, and yaw is around the z-axis, expressed in radians.
<parent> (required)
- The name of the parent link is a mandatory attribute.
- link The name of the parent link is the name of the link in the robot structure tree.
<child> (required)
- The name of the child link is a mandatory attribute.
- link The name of the child link is the name of the link in the robot structure tree.

<axis>(optional: defaults to (1,0,0))
- The joint's axis is in the joint's coordinate system. This is the axis of rotation (revolute joint), the axis of movement of the prismatic joint, and the standard plane of the planar joint. This axis is specified in the joint coordinate system. Modifying this parameter can adjust the axis around which the joint rotates. It is often used to adjust the rotation direction. If the model rotation is opposite to the actual one, just multiply by -1. Fixed and floating joints do not need this element.
- xyz(required) x , y , z x, y, zx, y, z components representing axis vectors, as normalized vectors.
<calibration> (optional)
- The reference point of the joint, used to correct the absolute position of the joint.
- rising (optional) When the joint is moving forward, the reference point triggers a rising edge.
- falling (optional) When the joint is moving forward, the reference point triggers a falling edge.
<dynamics>(optional)
- This element is used to specify the physical properties of the joint. Its value is used to describe the modeling performance of the joint, especially during simulation.

<limit> (Required when the joint is a rotation or translation joint)

This element is a joint kinematics constraint.
lower (optional, default to 0) Specify the attribute of the lower bound of the joint's motion range (the unit of the revolute joint is radians, and the unit of the prismatic joint is meters). This attribute is ignored for continuous joints.
upper (optional, defaults to 0) Specify the attribute of the upper bound of the joint's motion range (the unit of the revolute joint is radians, and the unit of the prismatic joint is the meter). This attribute is ignored for continuous joints.
effort (required) This property specifies the maximum force at which the joint will run.
velocity (required) This property specifies the maximum speed of the joint runtime.

<mimic>(optional)

This tag is used to specify a defined joint to mimic an existing joint. The value of this joint can be calculated using the following formula: value = multiplier * other_joint_value + offset
joint(required) The name of the joint to mimic.
multiplier(optional) Specify the multiplier factor in the above formula.
offset(optional) Specify the offset term in the above formula. Default value is 0

<safety_controller> (optional)

This element is a security control limit. The data under this element will be read into move_group, but it is invalid in practice. Move_group will skip this limit and directly read the parameter content under limit. At the same time, setting this element may cause planning failure.
soft_lower_limit (optional, defaults to 0) This attribute specifies the lower bound of the joint security control boundary, which is the starting limit point of the joint security control. This value needs to be greater than the lower value in the above limit.
soft_upper_limit (optional, defaults to 0) This attribute specifies the upper bound of the joint security control boundary, which is the starting limit point of the joint security control. This value needs to be less than the upper value in the above limit.
k_position(optional, defaults to 0) This attribute is used to describe the relationship between position and velocity.
k_velocity(required) This property is used to describe the relationship between force and velocity.

5673ade8eb00a28794557125b7d1c8cd332434a9

<<<<<<< HEAD 详细元素以及各个元素的作用可以前往 http://wiki.ros.org/urdf/XML/joint 进行查看

4 常用命令工具

在ROS中，有许多常用的命令行工具，这些工具可以帮助你进行开发、调试、管理ROS节点等。以下是一些常用的ROS命令行工具：

4.1 编译工作空间

======= Detailed elements and the role of each element can go to http://wiki.ros.org/urdf/XML/joint to view.

4 Commonly used command tools

In ROS, there are many commonly used command line tools, which can help you develop, debug, manage ROS nodes, etc. The following are some commonly used ROS command line tools:

4.1 Compile workspace

caktin_make

4.2 roscore

<<<<<<< HEAD

启动ROS主节点。在运行ROS节点之前，通常需要先启动roscore

Start the ROS master node. Before running a ROS node, you usually need to start roscore first

roscore

4.3 rosrun

<<<<<<< HEAD

运行指定的ROS节点。

Run the specified ROS node.

rosrun package_name node_name

4.4 roslaunch

<<<<<<< HEAD

使用Launch文件启动一个或多个ROS节点。

Use the Launch file to start one or more ROS nodes.

roslaunch package_name launch_file.launch

4.5 rosnode

<<<<<<< HEAD

查看正在运行的ROS节点信息。

View running ROS node information.

rosnode list
rosnode info node_name

4.6 rostopic

<<<<<<< HEAD

查看正在运行的ROS话题信息。

View information about running ROS topics.

rostopic list
rostopic echo topic_name

4.7 rosservice

<<<<<<< HEAD

查看和调用ROS服务。

View and call ROS services.

rosservice list
rosservice call service_name

4.8 rosparam

<<<<<<< HEAD

获取和设置ROS参数。

Get and set ROS parameters.

rosparam get parameter_name
rosparam set parameter_name value

4.9 rosmsg

<<<<<<< HEAD

查看ROS消息类型。

View ROS message types.

rosmsg show message_type

4.10 rosdep

<<<<<<< HEAD

安装ROS包的依赖项。

Install dependencies of ROS packages.

rosdep install package_name

<<<<<<< HEAD

4.11 环境变量

查看ROS_PACKAGE_PATH环境变量

4.11 Environment variables

View the ROS_PACKAGE_PATH environment variable

echo $ROS_PACKAGE_PATH

<<<<<<< HEAD ← 上一页 | 下一页 →

======= ← Previous Page | Next Page →

1 ROS工程结构

1.1 catkin工作空间

一个简单的工作空间如下所示：

1 ROS project structure

1.1 catkin workspace

1.2 ROS软件包

catkin_create_pkg命令会要求你输入package_name，如有需要还可以在后面添加一些需要依赖的其它软件包：

1.2 ROS software package

- 例如：

2 ROS通信架构

2.1 Master与node

1 Master

2 roscore

3 node

4 launch

启动master和多个node。

2.2 Service 与 Topic

1 Service

2 Topic

2.3 msg和srv简介

1 rosmsg

2 rossrv

3 URDF介绍

3.1 urdf文件描述

本处只截取部分代码进行展示：

3 Introduction to URDF

3.1 urdf file description

3.2 link部分

3.2.1 属性

3.2.2 元素

3.3 joint部分

3.3.1 joint的属性：

3.3.2 joint的元素

本属性用于说明力和速度之间的关系。

3.2 link section

3.2.1 Attributes

3.2.2 element

3.3 joint part

3.3.1 properties of joint:

3.3.2 elements of joint

4 常用命令工具

4.1 编译工作空间

4 Commonly used command tools

4.1 Compile workspace

4.2 roscore

启动ROS主节点。在运行ROS节点之前，通常需要先启动roscore

4.3 rosrun

运行指定的ROS节点。

4.4 roslaunch

使用Launch文件启动一个或多个ROS节点。

4.5 rosnode

查看正在运行的ROS节点信息。

4.6 rostopic

查看正在运行的ROS话题信息。

4.7 rosservice

查看和调用ROS服务。

4.8 rosparam

获取和设置ROS参数。

4.9 rosmsg

查看ROS消息类型。

4.10 rosdep

安装ROS包的依赖项。

4.11 环境变量

查看ROS_PACKAGE_PATH环境变量

4.11 Environment variables

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