Posted 2022-04-15Updated 2024-11-02Note3 minutes read (About 378 words)

Study note for ROS publisher.

Model of Topic

Publisher(turtle Velocity)
- –[Message(geometry_msgs::Twist)]–>
Topic (/turtle1/cmd_vel)
- –[Message(geometry_msgs::Twist)]–>
Subscriber(turtlesim)

Programming realization

Take turtlesim as the example.
We write a program acting like a publisher and sending controlling messages.

Create package

1 2	$ cd catkin_ws/src $ catkin_create_pkg learning_topic roscpp rospy std_msgs geometry_msgs turtlesim

can see:

1 2	$ ls CMakeLists.txt include package.xml src

How to realize a publisher?

Initialize ROS node
register node info from ROS Master, including name of the topic and msg type
create message data
publish message at a specific frequency

Code

create velocity_publisher.cpp file in learning_topic/src

#include <ros/ros.h>
#include <geometry_msgs/Twist.h>

int main(int argc, char *argv[])
{
    //init the node
    ros::init(argc,argv,"velocitypublisher");

    //create node handle
    ros::NodeHandle n;

    //create a publisher, who publish topic names '/turtle1/cmd_vel', message type 'geometry_msgs:Twist', queue length 10
    ros::Publisher turtle_vel_pub = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel",10);

    //set loop rate
    ros::Rate loop_rate(10);
    while (ros::ok()) {
        //initialize geometry_msgs:Twist msg
        geometry_msgs::Twist vel_msg;
        vel_msg.linear.x = 0.5;
        vel_msg.angular.z = 0.2;

        //publish msgs
        turtle_vel_pub.publish(vel_msg);
        ROS_INFO("Publish turtle velocity command at %0.2f m/s, %0.2f rad/s",
                vel_msg.linear.x,vel_msg.angular.z);

        //delay
        loop_rate.sleep();
    }
    return 0;
}

What is queue length?

msgs can be published very fast while the data transmission rate is limited, so the queue act as a buffer
first in, first thrown, keeping the remained msgs in the queue relatively new

Configure the compile rule of publisher

Steps:

set the code need to be complied and the generated excutable file
set the link library

Add two lines to learning\_topic/CMakeLists.txt (in build part):

1 2	add_executable(velocity_publisher src/velocity_publisher.cpp) target_link_libraries(velocity_publisher ${catkin_LIBRARIES})

Compile

$ cd ~/ROS_study/catkin_ws
$ catkin_make
$ source ./devel/setup.zsh
$ roscore
$ rosrun turtlesim turtlesim_node
$ rosrun learning_topic velocity_publisher

Then, you can see turtle:

And outputs:

...
[ INFO] [1650088100.376299177]: Publish turtle velocity command at 0.50 m/s, 0.20 rad/s
[ INFO] [1650088100.476312726]: Publish turtle velocity command at 0.50 m/s, 0.20 rad/s
[ INFO] [1650088100.576304995]: Publish turtle velocity command at 0.50 m/s, 0.20 rad/s
...

Posted 2022-04-12Updated 2024-11-02Note2 minutes read (About 347 words)

Regular-Expression

Studying note for regular expression

Definition

Regular expression describes a pattern of matching string
Can be used to detect/replace/take out specific substring

Syntax

symbol	description	example
^	match the beginning of he line
[ABC]	match all char in […]	[aeiou]: google runoob taobao
[^ABC]	match all except those in […]
[A-Z]	describe an interval	[a-z] matchs all lower case char
(…)	set groups
\1…\n	match the same elements as nth group
{n}	the front element repeats n times
{n,}	the front element repeats at least n times
{n,m}	the front element repeats at least n and at most m times
.	match any char except (\n,\r), same with [^\n\r]
\s\S	match all, \s:match all space char, \S:match all non space char, ‘return’ not included
\w	match letter,number,underline, equal to [A-Za-z0-9 ]
\cx	match the control char indicated by x(A-Z/a-z)	\cM: Control-M or return char
\f	match a page change char
\n\r	match a return symbol
\t	match a tab
\v	match a vertical tab
$	match the end of the string, to match $ itself, use $
*	match the front subexpression multiple or zero times, use \* to match *
+	match the front subexpression multiple or one times, use \+
.	match any single char except \n
[	mark the beginning of a []expression
?	match the front subexpression one or zero times, or indicate a non-greedy qualifier
\|	logic or

Application in Cpp

In cpp, we use std::regex to express regular expression, supporting ECMAScripts as default.

Match

Use regex_match() to match xml (or html) format:

std::regex reg("<.*>.*</.*>");

bool ret = std::regex_match("<xml>value</xml>",reg);
assert(ret);


bool ret = std::regex_match("<html>value</html>",reg);
assert(ret);

bool ret = std::regex_match("<xml>value<xml>",reg);
assert(ret);

Search

Use std::regex_search.
As long as there exists targets in the string, it will return.

std::regex reg("<(.*)>(.*)</(\\1)>");
std::cmatch m;
auto ret = std::regex_search("123<xml>value</xml>456", m, reg);
if (ret){
    for (auto& elem : m)
        std::cout<<elem<<std::endl;
}

Posted 2022-04-12Updated 2024-11-02Notea few seconds read (About 106 words)

VIM Snippets Customization

Studying note for customizing vim-snippets.

Install vim-snippets

See Github

Syntax

Module:

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2
3

snippet [trigger] ["Description"] [index]
[content]
endsnippet

Index:

Index	Description
b	trigger should be in the front of the line
i	trigger can be inside a word
w	trigger should be in the edge of two words
r	trigger can be a regular expression
A	auto trigger

Example

Generate a two column table:

snippet tb2 "Create table of two columns" b
| $1 | $2 |
|----|----|
| $3 | $4 |
| $5 | $6 |
endsnippet

snippet tbex2 "Create table of two columns" b
| $1 | $2 |
endsnippet

Or generate a code block for bash

snippet bbl "Bashblock" b
\`\`\`bash
\$ ${2:${VISUAL}}
\`\`\`
$0
endsnippet

Posted 2022-04-12Updated 2024-11-02Note3 minutes read (About 505 words)

ROS Orgmode Note

Study note for ROS
* Core Concept
** Node and ROS Master
*** Node
implement functions for purposes
support various language
can have thousands of nodes
*** ROS Master
mange the registion and name of various nodes
support(trace and record) communication between different nodes
for nodes to find each other
provide parameter server(store global variables...)[[about parameter]]
** Communication between nodes
|                    | Topic               | Service        |
|--------------------+---------------------+----------------|
| sync               | n                   | y              |
| model              | publish/subscribe   | service/client |
| protocol           | ROSTCP/ROSUDP       | ROSTCP/ROSUDP  |
| response           | n                   | y              |
| buffer             | y                   | n              |
| real-time          | weak                | strong         |
| nodes relationship | multi/one to multi  | one to multi   |
| scene              | data transformation | logic process  |
*** Topic
Node(publisher)->Topic(/example)&Message_Tyoe(std_msgs/String)->other ROS nodes(subscriber)
Message: define the data type and struct of data, defined by .msg file
async
*** Service
C/S model(Client/Server)
client send requests, server return response data
defined by .srv file, defines the structure of the requests and response
    ROS node(Service Server)
    ^  |response
request|  v
    ROS node(Service Client)
sync
** Parameter
<<about parameter>>
talker -> ROS master : setParam("foo",1)
listener -> ROS master: getParam("foo")
ROS master ->listener: {"foo",1}

multiple variable dictionary
for storing static nonbinary configuration, not suitable for dynamic
** File system
*** package
Basic unit in ROS, include the src of nodes, cfg, data def
*** package manifest
record the basic information of packages
*** Meta packages
orgnize multi packages for one common purpose
* Commond Line Tools
** rqt_graph
visualize tool
display the calculate process graph
** rosnode
display node information
*** rosnode list
list all node
default node /rosout
*** rosnode info /turtle_sim
show info of a node
** rostopic
usage like rosnode(list,info)
*** rostopic pub /../.. data_structure data 
publish message as a topic
add -r num to repeat sending at rate num/s
** rosmsg
*** rosmsg show data_structure
show the data structure
** rosservice 
| commond addition       |                                   |
|------------------------+-----------------------------------|
| list                   | list all service the node provide |
| call service_name data |                                   |
** rosbag
| command addition        |                                               |        |                 |
|-------------------------+-----------------------------------------------+--------+-----------------|
| record -a -O cmd_record | record the topic data in the system           | -a:all | -O as a package |
| play cmd_record.bag     | play the recorded data of previous simulation |        |                 |
|                         |                                               |        |                 |
* setup workspace and function package
** workspace
*** overview
| src     | source space  |                         |
| build   | build space   | no need to touch        |
| devel   | develop space | script, executable file |
| install | install sapce |                         |

work space folder/
  src/
    CmakeLists.txt
    package_1/
      CmakeList.txt
      package.xml
      ...
    package_n/
      CmakeList.txt
      package.xml
      ...
  build/
    CATKIN_IGNORE
  devel/
    bin/
    etc/
    include/
    lib/
    share/
    .catkin
    env.bash
    setup.bash
    setup.sh
    ...
  install/
    bin/
    etc/
    include/
    lib/
    share/
    .catkin
    env.bash
    setup.bash
    setup.sh
    ...
*** setup
**** establish ws
mkdir -p ./catkin_ws/src
cd ./catkin_ws/src
catkin_init_workspace
**** compile ws
cd ./catkin_ws/
catkin_make -DPYTHON_EXECUTABLE=/usr/bin/python3
catkin_make install
**** set env variables
source devel/setup.bash
**** check env variables
echo $ROS_PACKAGE_PATHH
** fucntion package
*** setup
| establish package | cd ./src                                                                   |                                       |
|                   | catkin_create_pkg <pkg_name> [depend1] [depend2].. (rospy,roscpp,std_msgs) |                                       |
| source env path   | source devel/setup.bash                                                    | make sure that ros can detect the pkg |

*** package.xml
| label                        | description                                         |
|------------------------------+-----------------------------------------------------|
| <name>                       |                                                     |
| <version>                    |                                                     |
| <description>                |                                                     |
| <maintainer email="">        | maintainer's name and email                         |
| <license>                    |                                                     |
| <buildtool depend>           | usually catkin                                      |
| <build_depend>/<exec_depend> | package dependencies ,usually roscpp rospy std_msgs |
*** CmakeList.txt
TODO

Posted 2022-04-11Updated 2024-11-02Notea minute read (About 211 words)

How I set up my blog site

This post record the steps I set up this blog site.

Catalog

Env preparation
Github
- Connection
- Setup Github Pages repository
Install Hexo
Deploy to Github server

Env preparation

Installation

Install Node.js
Install Git

Use following command to confirm:

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3

$ node -v
$ npm -v
$ git --version

Github

Connection

Create and copy SSH key:

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2
3

$ ssh-keygen -t rsa -C "GitHub email"
$ cd ~/.ssh
$ vim id_rsa.pub

Copy the contents

Go to Github -> Settings and Add SSH key

Confirm the connection:

1	$ ssh -T git@github.com

Setup Github Pages repository

Create Username.github.io(your URL)

Install Hexo

1	$ npm install -g hexo-cli

Setup a local workspace:

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3

$ git init
$ hexo init
$ npm install

launch local server:

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3

$ hexo cl
$ hexo g
$ hexo s

or use following command to specify port:

1	$ hexo server -p 5000

visit http://localhost:4000

Deploy to Github server

Install hexo-developer-git:

1	$ npm install hexo-deployer-git --save

edit _config file’s Deployment part:

deploy:
  type: git
  repository: git@github.com:Chen-Yulin/Chen-Yulin.github.io.git
  branch: master

then run in bash:

$ hexo d

Posted 2022-04-04Updated 2024-11-02Notea minute read (About 123 words)

Hexo Start

Welcome to Hexo! This is your very first post. Check documentation for more info. If you get any problems when using Hexo, you can find the answer in troubleshooting or you can ask me on GitHub.

Quick Start

Create a new post

1	$ hexo new "My New Post"

More info: Writing

Run server

1	$ hexo server

More info: Server

Generate static files

1	$ hexo generate

More info: Generating

Deploy to remote sites

1	$ hexo deploy

More info: Deployment

Model of Topic

Programming realization

Create package

Code

Configure the compile rule of publisher

Compile

Definition

Syntax

Application in Cpp

Match

Search

Install vim-snippets

Syntax

Example

Catalog

Env preparation

Github

Connection

Setup Github Pages repository

Install Hexo

Deploy to Github server

Quick Start

Create a new post

Run server

Generate static files

Deploy to remote sites

Archives

Recents

Tags