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ROS.md

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ROS

rospack find [package name] -> returns the path

roscd [locationname[/subdir]] : allows you to cd directly to a package

​ only finds packages within ROS_PACKAGE_PATH

rosls [locationname[/subdir]]

package.xml includes all teh info. description, maintainers, dependencies, etc.

catkin_make - builds projects '

folders:

​ build - build space, where cmake adn make are called to build packages

​ devel - devel space, where executables and libraries go

roscore - run when you're using ROS

​ needs wifi

to play a rosbag: rosbag play ____ -l (looping)

rosnode list

​ lists nodes

​ always lists rosout (logs nodes' debugging output)

​

rosnode info [node]

​ lists info

rosrun [package name] [node name]

rqt_graph creates dynamic graph of what's going on in system

rostopic -h (evokes avialalbe sub commands)

​ rostopic echo [topic] - shows data published

​ rostopic pub - pubishes messages to a given topic

​ rostopic pub -[number of messages before exiting] [name of topic to publish to] [message type] [arguments]

​ pub [name of topic] [message type] -r 1 (sends 1 Hz)\

​ rostopic hz [topic] - rate at which data is published

rosservice - send request, receive response

​ list (lists all the services)

​ rosservice type /spawn | rossrv show -> shows info for the service

rosparam

Concepts:

​ package: smallest unit to produce. includes a full project

​ nodes - there's a lot. usually one for each sensor

​ master - ROS master provides name registration, lookup to rest of computation graph .

​ parameter server

​ messages

​ passed by nodes

​ data structure (primitive types, arrays, etc.)

​ routed via transport system with publish and subscribe semantics

​ published to a topic

​ publisher and subscriber must send and receive the same type of message

​ topics - name that is used to identify content of message =

​ node will subscribe to a topics

​ services: defined by a pair of message structures. one for request and one for reply.

​ bags - format for saving and playign back ro smessage data

​ client libraries: python and c++

rosnodejs

Resources: www.wiki.ros.org/rosnodejs/

rosnodejs is a javascript client library for ROS, built on node.js runtime. It allows javascript projects to communicate with ROS.

initialization

to start node:

//used by plusAI
rosnodejs.initNode('my_node').then((nodeHandle) => { 
  //do stuff
});

or

rosnodejs.initNode('my_node').then(() => {
  let nh = rosnodejs.nh;
  //do stuff
});

initNode accepts a second object for other options, such as

  • rosMasterUri
  • onTheFly
  • logging
  • node

messages

###message generation

using Catkin (kinetic version and later)

built when running catkin_make

package_name/msg/Foo.msg -> package_name.msg.Foo

package_name/srv/bar.srv -> package_name.srv.bar

files required through rosnodejs

const std_msgs = rosnodejs.require('std_msgs');
const StringMsg = std_msgs.msg.String;

const SetBool = rosnodejs.require('std_srvs').srv.SetBool;

on the fly

rosnodejs.initNode('my_node', {onTheFly: true});

message initializaton

directly assign values to embedded messages:

const msg = new geometry_msgs.msg.PoseStamped();
msg.header.frame_id = 'base';
const msg = new std_msgs.msg.String({data: 'Hello'}); //accepts arguments for fields

publishers

Using a NodeHandle from rosnodejs:

const nh = rosnodejs.nh;
const pub = nh.advertise('/topic', 'std_msgs/String', {options}); //publishes message with type string

initialization

Options:

  • latching (default = false). if true, last message published is saved and sent to future subscribers that connect
  • tcpNoDelay (no delay on publisher's socket)
  • queueSize (default = 1). consecutive calls will add new messages up to queueSize, then older messages are dropped off
  • throttleMs (default = 0). minimum interval at which publisher's outgoing message queue is handled. if negative, any call to publish will be handled immediately.

publishing

if type string, then:

const msg = new std_msgs.msg.String();
msg.data = 'Hello!';
pub.publish(msg);

//OR

pub.publish({ data: 'Hello!' }); //generic object

publishers are also event emitters. (part of Node.js)

can add handlers for the following events:

  • registered (when publisher has successfully been registered with master)
  • connection (when a new subscriber connects to publisher)
  • disconnect (when subscriber disconnects from publisher)
  • error (on the publisher)

subscribers

const std_msgs = rosnodejs.require('std_msgs');

const nh = rosnodejs.nh;
const sub = nh.subscribe('/topic', std_msgs.msg.String, () => {});

Options:

  • queueSize (default = 1)
  • throttleMs (default = 0)

subscribers are also event emitters.

can add handlers for events:

  • registered (subscriber with master)
  • message (when new message is ready to be handled)
  • connection (new publisher with subscriber)
  • disconnect
  • Error (with subscriber)

shutdown

process.exit(), SIGINT, rosnodejs.shutdown()

shutdown hooks:

​ rosnodejs.on('shutdown', function() {});

​ rosnodejs.once('shutdown', function() { });

​ rosnodejs.removeListener('shutdown', function(){});