ROS入门指南：《notes-ros》基础教程

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"notes-ros是面向ROS初学者的基础文档，旨在辅助理解ROS并补充在线教程。这份文档在不断地编辑和完善，包含多个版本的历史更新，详细介绍了ROS的基本概念、配置、节点、话题等核心内容，并提供了C++编写简单ROS程序的指导。" ROS (Robot Operating System) 是一个开源操作系统，用于构建机器人软件。对于初学者来说，了解ROS的基本概念至关重要。文档《notes-ros》从以下几个方面深入浅出地讲解了ROS： 1. **ROS基础知识** - **获取ROS信息**：这部分内容可能涵盖如何查找ROS相关的文档、库和工具，以及如何获取系统信息。 - **配置ROS，探索包和创建工作区**：ROS的工作区和包管理是其核心特性之一，这部分会教读者如何设置ROS环境，找到和访问ROS包，以及如何创建自己的工作区和包。 2. **主节点（Masters），节点（Nodes），话题（Topics），发布者（Publishers）和订阅者（Subscribers）** - **启动roscore**：roscore是ROS系统中的核心组件，它作为节点间通信的中心。 - **启动节点**：ROS系统中的计算任务由独立的节点执行，这部分会解释如何启动和管理这些节点。 - **检查图形结构**：通过rosgraph命令可以查看整个ROS系统的通信图，理解节点之间的连接关系。 - **检查主题和观察消息**：ROS中的数据交换通过话题进行，这部分将教授如何监控话题和分析通过话题传输的数据。 3. **用C++编写简单的ROS程序** - **ROS的“Hello, World!”**：类似于编程语言学习的传统起点，这里可能会介绍如何编写一个简单的ROS节点，向用户打招呼。 - **编译你的包**：ROS使用catkin工具链来构建和管理项目，这部分会教给读者如何配置和编译ROS包，使其能够在系统上运行。 4. **其他高级概念和工具** - 随着文档的不断更新，可能会涵盖更多内容，如服务（Services）、参数服务器（Parameter Server）、动作库（Actions）、 bag文件（用于数据记录和回放）以及各种诊断工具等。通过《notes-ros》，初学者能够逐步理解ROS的核心机制，并获得实践操作的经验，从而为后续更复杂的机器人项目打下坚实基础。此外，该文档的持续更新确保了内容的时效性和完整性，对于ROS的学习者来说是一个宝贵的资源。

to those messages. When you’re exploring a new ROS system, the “All topics” option is a useful way to

discover what topics are available for

your

programs to use to communicate with the existing nodes.

Now we can understand at least part of how the teleoperation system works. When you press a key, the

/teleop turtle node publishes messages with those movement commands on /turtle1/command velocity,

and the turtlesim node receives those messages, and simulates the turtle moving with the requested ve-

locity. The important points here are that

• The simulator doesn’t care (or even know) which program publishes those command velocity messages.

Any program that publishes on that topic can control the turtle.

• The teleoperation program doesn’t care (or even know) which program subscribes to the command velocity

messages it publishes. Any program that subscribes to that topic is free to respond to those commands.

3.4 Inspecting a topic and observing its messages

You can see the actual messages that are being published using the rostopic command:

rostopic echo /turtle1/command velocity

This command will dump any messages published on the given topic to the terminal. Here’s some example

output:

linear: 2.0

angular: 0.0

---

linear: 0.0

angular: -2.0

---

linear: 2.0

angular: 0.0

---

Each --- line shows the end of one message and the start of another; in this case there were three messages.

You can learn more about a topic using a command like this:

rostopic info /turtle1/command velocity

The output might look like this:

Type: turtlesim/Velocity

Publishers:

/teleop turtle (http://donatello:58531/)

Subscribers:

/turtlesim (http://donatello:53925/)

/rostopic 17170 1358263206987 (http://donatello:38130/)

First, you’ll notice also that rostopic is listed as a subscriber to this topic. This is because rostopic

echo—which was still running when I did this rostopic info—is a node itself, and it works just like

any other node: It subscribes to the topic you ask about, and prints out any messages that are published

that topic.

However, the important part about the output above is the ﬁrst line, which shows the data type of the

messages on this topic. In this case, the data type is turtlesim/Velocity. To see details about a ROS

data type, use a command like this:

CSCE574 – Spring 2013 Notes on ROS 9 of 51

4 Writing Simple ROS Programs in C++

Now that you know how to conﬁgure your account for ROS, and how to work with nodes and topics,

it’s time to write your ﬁrst ROS programs. You should ﬁrst make sure to have a correctly conﬁgured ROS

workspace, and a package within that workspace—I called my package simple_examples, but any name

is ﬁne—for testing.

4.1 Hello, ROS!

Here’s a ROS version of the standard “Hello, world!” program.

#include <ros/ros.h>

int main(int argc, char

argv) {

ros::init(argc, argv, "hello ros");

ros::NodeHandle n;

ROS INFO("Hello, ROS!");

ros::spinOnce();

}

Comments:

• This source ﬁle, named hello.cpp, belongs in your package folder, right next to your package.xml

and CMakeLists.txt. (The tutorials suggest creating a src directory within your package direc-

tory, but this is not really necessary.)

• The include ﬁle ros/ros.h includes most of the standard ROS classes. You’ll want to include it in

every ROS program that you write.

• The ros::init function initializes the ROS library. Call this once at the beginning of your program

to set things up. The last parameter is a string containing the name of your node.

• The ros::NodeHandle object is the main mechanism that your program will use to interact with

the ROS system. Creating this object registers your program as a node with the ROS master. When

the object is destroyed, your program de-registers itself from the master.

• The ROS_INFO line is a shorthand for publishing a message to the topic rosout. You’ll see these on

your terminal screen, and you can also use rostopic echo /rosout to see the details. Those

rosout messages actually contain a bit more information that just the string message; after you

compile and run this program, you can use the tools from Section 3.4 to explore the details for yourself.

• The ros::spinOnce() function gives the ROS library control of your program for a short time. This

is when messages are actually sent and received.

4.2 Compiling Your Package

How can you compile and run this program? This is handled by ROS’s build system, called catkin. There

are three steps:

1. First, you need to edit the package’s CMakeLists.txt ﬁle. The purpose of this ﬁle is to enable catkin

to know where to ﬁnd include ﬁles and libraries for your executable. Here’s a minimal version of this

ﬁle that should work for our “Hello, ROS” example.

cmake_minimum_required(VERSION 2.8.3)

project(simple_examples)

find_package(catkin REQUIRED COMPONENTS roscpp)

catkin_package()

include_directories(include $catkin_INCLUDE_DIRS)

add_executable(hello hello.cpp)

target_link_libraries(hello ${catkin_LIBRARIES})

CSCE574 – Spring 2013 Notes on ROS 11 of 51

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