AIRWiki - User contributions [en]

Bureaucracy

2019-11-06T20:06:20Z

GiulioFontana:

''This page contains the things you need to know and do to be allowed to work in the AIRLab. It is especially targeted to students.''

== HOW TO become a registered user of AIRWiki ==
To become one of the [[registered users]], you must request a user account for the AIRWiki. To do that, you can ask your Advisor or co-Advisor (the procedure to create a new user is described [[Bureaucracy#HOW_TO_create_a_new_AIRWiki_user|at the bottom of this page]]).


If you are a student beginning her/his work within the AIRLab, please note that you ''must'' be a registered user before you can even enter the Lab. You must also be aware that anything you put into the [[Layers|public layer]] of AIRWiki will be '''published on the internet and visible by all the world'''. Always keep in mind the [[Registered users#Warnings|warnings]]!

== HOW TO get the authorization to access the Lab ==
''Note: renewal for guests is not done through this procedure. The guest should go instead to [http://www.deib.polimi.it/personale/dettaglio.php?id_persona=262&id_sezione=&lettera=C&idlang=ita Ms Laura Caldirola] and start the procedure.''

You cannot access the AIRLab without being authorized. You can get the authorization by following these steps:

# '''Read carefully the [[Safety norms]] and the [[AIRLab rules]]'''. Those documents are written in Italian: if you aren't able to read them, ask your Advisor.
# '''Become a registered AIRWiki user''' (see how at the [[Bureaucracy#HOW_TO_create_a_new_AIRWiki_user|bottom of this page]]). This also creates an empty personal page for you (you can reach it from [http://airwiki.ws.dei.polimi.it/index.php/People here]).
# '''Fill in your user page''' with your personal data and photo (read [[HOWTO fill in your AIRWiki user page|here]] how).
# '''Set up an AIRWiki page for your project''' you will be working on, if it does not exist yet (directions for that are [[Projects - HOWTO | here]]).
# '''Send an e-mail to [http://www.deib.polimi.it/personale/dettaglio.php?id_persona=262&id_sezione=&lettera=C&idlang=ita Ms Laura Caldirola]''' (''laura.caldirola@polimi.it'') requesting the access to AIRLab, specifying: (i) your advisor's name; (ii) the lab location (e.g., building 7 or building 21); (iii) the duration of your thesis or project (ask your advisor for this); (iv) your personal code ("codice persona") as a member of Politecnico di Milano.
# '''Send an e-mail to professor Bonarini''' (''andrea.bonarini@polimi.it'') declaring that you have read and understood the [[safety norms]] and the [[AIRLab rules]].
# '''Get your personal Politecnico di Milano badge enabled''' for access to AIRLab by [http://www.deib.polimi.it/ita/personale/dettagli/91386 Ing. Fausto Berton] (his office is at DEIB, ground floor). He will send you an e-mail message to ask you to go to his office to sign a paper and finalize the process. If you do not receive this message within three days, please contact him directly. ''[Note: this last phase of the procedure changed from 2016-11-30. Before, the access badge was different from the student's.]''

It's done. Now, you are an authorized AIRLab student. Your badge should open the AIRLab doors. Hooray!

REMEMBER: to enter there you declared to follow the rules, and in particular to keep a proper behavior, be responsible and ... enjoy the AIRLab!

== HOW TO connect your laptop to the Internet ==

In AIRLab you have free connection both wired and WI-FI.

== HOW TO create a new AIRWiki user ==
Sysop users (sysop users are [[Special:ListUsers/sysop|these]]; if you are curious about what being a sysop means, [http://www.mediawiki.org/wiki/Help:Sysops_and_permissions read here]) can create new AIRWiki users. This is necessary, for instance, to introduce a student to the AIRLab.
Provided that you are a Sysop, to create a new AIRWiki user account you must:
* log in to the AIRWiki
* go to [[Special:UserLogin|the login/create account page]]
* click on "create new account"
* fill in the data of the new user (the username should comply with AIRWiki's convention of "NameSurname").

This procedure also creates the personal page for the new user, but 'does not' fill in such page. The new user will have to fill it in by herself ([[HOWTO_fill_in_your_AIRWiki_user_page|see here to learn how]]).

AIRWiki

2019-07-21T14:44:50Z

GiulioFontana:

[[Image:AIRLabStudentiQuadrupedeLow.jpg |thumb|right|300px|Students at AIRLab.]]

<div align="right">
Welcome to AIRLab!
</div>

This is the [http://en.wikipedia.org/wiki/Wiki wiki] supporting AIRLab, the '''Artificial Intelligence and Robotics Laboratory''' at the [http://www.deib.polimi.it/eng/home-page Department of Electronics, Information and Bioengineering] of [http://www.english.polimi.it/ Politecnico di Milano].

AIRLab was established by prof. Marco Somalvico in 1971 as one of the first groups of researchers in Italy working on Artificial Intelligence, Robotics and Computer Vision.

[[People|Researchers]] working at AIRLab have always followed and leaded the evolution of AI and Robotics. The research areas we are presently focusing on are listed [[Research Areas|here]].

We have always worked both on theoretical aspects and on applications, developed in [[Funded Projects|projects]] funded by national and international agencies and companies.

AIRLab [[People|professors]] presently manage one of the [[Teaching|largest curricula]] in Italy on AI and Robotics, producing each year more than 50 master theses and about 10-15% of the PhD theses of the [http://www.deib.polimi.it/eng/computer-science-and-engineering Computer Science and Engineering Section] at [http://www.deib.polimi.it/eng/home-page DEIB].

Many activities at AIRLab are covered by media as soon as they attract interest. You may find [[Media Coverage|here]] links to some of the past articles on newspapers and magazines.

AIRLab participates to the EUrobotics AISBL, and is one of the [http://robotics.polimi.it robotics labs of Politecnico di Milano].

AIRWiki supports many activities of researchers and students working at AIRLab. Follow the links at he "AIRWiki" tab.

AIRLab also occasionally participates at [[Events|events]].

HOWTO fill in your AIRWiki user page

2019-04-11T08:01:01Z

GiulioFontana: Reverted edits by AndreaBolognesi (talk) to last revision by AndreaBonarini

To do '''anything''' in the AIRLab, even to enter one of [[The Labs|its sites]], you must become one of the [[registered users]] of the AIRWiki and fill in your personal page in the [[Special:Listusers]] page.

To do that:
* log in to the AIRWiki (just use the link on top RIGHT of the [[Main Page]]);
* you should find your user name at the top of the page;
* click on that link and select 'Edit';
* open in another tab a page of another student to copy the form that is there (edit and copy the text) and paste it in your user page;
* open another tab on airwiki, select 'Upload file' from the options in the bottom line and upload your photo, copy the name of the file;
* fill in the frame in your user page with your data, including the name of the photo file (select your category: students have to select Student);
* among the information required to students is a link to their project page, which has to be generated following the instructions available [[Projects - HOWTO | here]] to obtain access to AIRLab
* feel free to edit the text of your personal and project pages as you like.

By default user pages are not accessible to unregistered users. If you want your user page to be visible to anyone see [[HOWTO make your user page public]].

Resources

2019-03-29T09:47:29Z

GiulioFontana:

==== Writing and Reading ====
* [[Tesi|How to write a thesis?]] Suggestions to prepare your thesis (only in Italian for now... translators are welcome!).
*[[ThesisPresentation|How to write slides and make a presentation]]
* [[Suggestions to write well]] can help to produce a good thesis, as well as good scientific publications in general. Here is the part of the 14 steps to write well found on the [http://www.sfedit.net San Francisco Edit company site] that Andrea Bonarini shares.
* Other suggestions to write a good paper that get accepted are on the [https://www.publishingcampus.elsevier.com/pages/3/Colleges/College-of-Skills-Training.html Elsevier site].
* You can access '''all the papers''' for which Politecnico has bought a subscription even when you are at home if you enable the [http://www.asi.polimi.it/rete/proxy/index.html Politecnico proxy]. The instruction page is provided by the nice people of [http://www.asi.polimi.it/ ASI] in Italian only. For an English version of the page, try to poke them if you can find how to get in touch with them.
* [[Tips for editors]] of AIRWiki are also collected by this community, just to help to understand some of the hidden beauty of semantic WIKIs.

==== Software and programming ====
* Once you have finished your work you should deliver it on the [[AIRLab Repository]]
* How to get rid of Delay in Arduino (Please, do this) [https://learn.adafruit.com/multi-tasking-the-arduino-part-1 Part1][https://learn.adafruit.com/multi-tasking-the-arduino-part-2 Part2]
* If you do not know Arduino or would like to understand how to use it at best, you may refer to [https://learn.adafruit.com/category/learn-arduino The Adafruit lessons] or directly to the less clear, but "official" [http://arduino.cc/en/Main/HomePage Arduino pages].
* [http://www.zeppelinmaker.it/arduino100/ Here] are 100 videos explaining basics of using Arduino and useful tricks .
* Go to our [[ROS HOWTO|ROS HOWTO page]] for advice and tutorials about ROS (Robot Operating System)
* Someone wrote some advice about [[Writing Good Code|writing code]]
* Info about [[Mathematica]]
* How to plot using gnuplot in your C/C++ project [[Gnuplot in cpp]]
* The AIRLab guide about [[Getting Started With PIC(TM) MCU]]
* Howto on [[VCSBC4018 vision board]]
* A few resources on [[Low Cost RTK GPS|Low Cost RTK GPS]] that might be useful

==== Hardware ====
* The [[Optitrack]] use guide
* Go to [[What's in the AIRLab]] if you are looking for stuff in the lab
* Need some component that isn't in the AIRLab for your project? Please add a row in the [[Shopping list]] and ask your advisor or [[User:GiulioFontana|Giulio Fontana]].
* Need to design a new robot and have no ideas bout how to select the basic elements? Have a look [http://www.robotshop.com/blog/en/how-to-make-a-robot-lesson-1-3707 here] and then talk with your advisor, before taking any decision.
* [https://learn.sparkfun.com/tutorials/light-emitting-diodes-leds?_ga=2.106364163.1818881530.1494048956-1750281731.1493634615 Tutorial on LED selection and use.]
* Some practical [http://www.instructables.com/id/Lithium-Polymer-Etiquette/ hints about LiPo Batteries]
* Need to learn '''how to solder'''? Here's a [http://mightyohm.com/files/soldercomic/FullSolderComic_EN.pdf handy comic] explaining the basics. Other useful links: [http://www.wireless.hackaday.com/2007/10/26/how-to-introduction-to-soldering/ 1] [http://www.wireless.hackaday.com/2007/10/28/followup-soldering-how-to/ 2] [http://www.make-digital.com/make/vol01/?pg=166 3]
* Need the US name for that bit of mechanics? Use [http://www.boltdepot.com/fastener-information/Printable-Tools/Type-Chart.pdf this useful chart]. By the way, [http://www.boltdepot.com/fastener-information/Printable-Tools/ at the same place] you can find other useful stuff of the same type.
* [http://www.instructables.com/id/Complete-Motor-Guide-for-Robotics/ All about motors]
* Small tutorial on (motor choices, wheel diameter, etc) [https://www.societyofrobots.com/mechanics_dynamics.shtml mechanics for mobile robot design]
* Tutorial on designing and making [https://www.societyofrobots.com/robot_omni_wheel.shtml Omni-wheeled Robots ]
* Tutorial on [http://www.instructables.com/id/433-MHz-Coil-loaded-antenna/ making 433MHz antennas] which largely improve the performance of transmitters/receiveirs.

==== Shops ====
* Some useful addresses and links about shops, stores, factories, online catalogues. With some of them we have partnerships for discounts. You can find information [[Shops| here]].

==== Version Control (GIT e SVN) ====
* piccola guida a [[Git | git]]
* piccola guida a [[Svn | svn]]

==== Producing videos and publishing them ====
* Usually, at the end of the project, people tend to produce a video and put it on the web. The best way to do this is to [[produce a video]] and then send it to [[User:AndreaBonarini | Andrea Bonarini]] to have it published on the YouTube channel of the AIRLab. Then you can put the link wherever you want, hopefully also in the page of your project on AIRWiki, as done, e.g. in [[ROBOWII]]

==== Where can I test my robot? ====
Usually, experiments are done within the space of our labs ([[The_AIRlab_sites|see here]]).

==== Hardware configuration ====
* Dei Phd-room (T11) printer configuration [[DeiPhdRoomPrinter | instructions]].

==== For AIRWiki Administrators ====

* [[AIRWiki:AdminFAQ]] (FAQs about common admin tasks such as '''adding users''', changing passwords, user renaming, etc.)
* [[Airpaper]] (writing a paper? This is a tool to share it with the other authors)
* [[DEI_Subversion_Administration]] (this is mainly for faculties)
* [[AIRWiki:Main]] (information about this specific AIRWiki installation)
* Are you having problems updating semantic information in the Wiki (i.e. you update it but it is not reflected on the rest of the website)? [[SemanticPropagation|Check this]] link for a possible solution to your problem.

==== Miscellanea (uncategorized) ====
* If you are searching the homepage of a DEI professor (or PhD Student) try this [http://mycroft.mozdev.org/download.html?name=dei+people&skipcache=yes Mozilla Firefox plugin].
* For [http://ph.dei.polimi.it/phday PhDay08] we've set up an [http://www.easychair.org Easychair] account for paper reviews. Here's a little [[EasyChair Reviews|tutorial for reviewers]] that might be useful in case you have to review somehing/teach someone how the system works.
* Useful phone numbers, download [[Media:ElencoTelefonico.odt.zip|ODT]] document or [[Media:ElencoTelefonico.pdf|PDF]].
* To remove from a surface any sticky remains of the glue or tape you used to affix something to it (e.g., the markers used by [[LURCH - The autonomous wheelchair|LURCH]]): try [http://www.henkel.it/adesivi/schede/pdf/TDS_Pattex_Rimuovicolla.pdf this] (Pattex Rimuovi Colla). It doesn't damage (most) surfaces.
* [[Recipes]] (yes, REAL recipies of special food) from people at AIRLab
* Sometimes, some ''geeky fun'' is all you need. [[Humour|Find it here!]]
* Wanna learn something, use [http://www.cheatography.com/ cheatsheets]!
** Matt [http://www.cheatography.com/spaceduck/cheat-sheets/coffee-drinks-and-machines/ likes coffes]
** Giulio [http://www.cheatography.com/fredv/cheat-sheets/eq-tips/ is an equilibrated person]
** ...

Resources

2019-03-29T09:47:06Z

GiulioFontana:

File:GiorgioLuparia.jpg

2018-10-16T07:18:53Z

GiulioFontana: GiulioFontana uploaded a new version of "File:GiorgioLuparia.jpg"

Bureaucracy

2017-09-12T13:33:19Z

GiulioFontana: /* HOW TO get the authorization to access the Lab */

''This page contains the things you need to know and do to be allowed to work in the AIRLab. It is especially targeted to students.''

== HOW TO become a registered user of AIRWiki ==
To become one of the [[registered users]], you must request a user account for the AIRWiki. To do that, you can ask your Advisor or co-Advisor (the procedure to create a new user is described [[Bureaucracy#HOW_TO_create_a_new_AIRWiki_user|at the bottom of this page]]).
If you need more information, send an email to eynard (at) elet (dot) polimi (dot) it.


If you are a student beginning her/his work within the AIRLab, please note that you ''must'' be a registered user before you can even enter the Lab. You must also be aware that anything you put into the [[Layers|public layer]] of AIRWiki will be '''published on the internet and visible by all the world'''. Always keep in mind the [[Registered users#Warnings|warnings]]!

== HOW TO get the authorization to access the Lab ==
''Note: renewal for guests is not done through this procedure. The guest should go instead to [http://www.deib.polimi.it/personale/dettaglio.php?id_persona=262&id_sezione=&lettera=C&idlang=ita Ms Laura Caldirola] and start the procedure.''

You cannot access the AIRLab without being authorized. You can get the authorization by following these steps:

# '''Read carefully the [[Safety norms]] and the [[AIRLab rules]]'''. Those documents are written in Italian: if you aren't able to read them, ask your Advisor.
# '''Become a registered AIRWiki user''' (see how at the [[Bureaucracy#HOW_TO_create_a_new_AIRWiki_user|bottom of this page]]). This also creates an empty personal page for you (you can reach it from [http://airwiki.ws.dei.polimi.it/index.php/People here]).
# '''Fill in your user page''' with your personal data and photo (read [[HOWTO fill in your AIRWiki user page|here]] how).
# '''Set up an AIRWiki page for your project''' you will be working on, if it does not exist yet (directions for that are [[Projects - HOWTO | here]]).
# '''Send an e-mail to [http://www.deib.polimi.it/personale/dettaglio.php?id_persona=262&id_sezione=&lettera=C&idlang=ita Ms Laura Caldirola]''' (''laura.caldirola@polimi.it'') requesting the access to AIRLab, specifying: (i) your advisor's name; (ii) the lab location (e.g., building 7 or building 21); (iii) the duration of your thesis or project (ask your advisor for this); (iv) your personal code ("codice persona") as a member of Politecnico di Milano.
# '''Send an e-mail to professor Bonarini''' (''andrea.bonarini@polimi.it'') declaring that you have read and understood the [[safety norms]] and the [[AIRLab rules]].
# '''Get your personal Politecnico di Milano badge enabled''' for access to AIRLab by [http://www.deib.polimi.it/ita/personale/dettagli/91386 Ing. Fausto Berton] (his office is at DEIB, ground floor). He will send you an e-mail message to ask you to go to his office to sign a paper and finalize the process. If you do not receive this message within three days, please contact him directly. ''[Note: this last phase of the procedure changed from 2016-11-30. Before, the access badge was different from the student's.]''

It's done. Now, you are an authorized AIRLab student. Your badge should open the AIRLab doors. Hooray!

REMEMBER: to enter there you declared to follow the rules, and in particular to keep a proper behavior, be responsible and ... enjoy the AIRLab!

== HOW TO connect your laptop to the Internet ==

In AIRLab you have free connection both wired and WI-FI.

== HOW TO create a new AIRWiki user ==
Sysop users (sysop users are [[Special:ListUsers/sysop|these]]; if you are curious about what being a sysop means, [http://www.mediawiki.org/wiki/Help:Sysops_and_permissions read here]) can create new AIRWiki users. This is necessary, for instance, to introduce a student to the AIRLab.
Provided that you are a Sysop, to create a new AIRWiki user account you must:
* log in to the AIRWiki
* go to [[Special:UserLogin|the login/create account page]]
* click on "create new account"
* fill in the data of the new user (the username should comply with AIRWiki's convention of "NameSurname").

This procedure also creates the personal page for the new user, but 'does not' fill in such page. The new user will have to fill it in by herself ([[HOWTO_fill_in_your_AIRWiki_user_page|see here to learn how]]).

User:LucaBascetta

2017-09-12T09:55:18Z

GiulioFontana:

{{Prof
|category=Prof
|firstname=Luca
|lastname=Bascetta
|photo=LucaBascetta.jpg
|email=luca.bascetta@polimi.it
|resarea=
|status=active
}}

Associate Professor in Automatic Control at the School of Industrial and Information Engineering of Politecnico di Milano.

Prof. Bascetta currently teaches, at Politecnico di Milano, Fundamentals of Automatic Control to Aerospace Engineering students and Automatic Control to Mechanical Engineering students.

His research interests include industrial and mobile robotics, visual serving and all the problems related to motion control systems.

2016-11-09T09:37:57Z

GiulioFontana: /* ROS in AIRWiki */

= ROS in AIRWiki =
The page you are reading is an introduction to ROS. If you are a ROS beginner, we suggest that you start from it. AIRWiki pages dedicated to ROS users also include more advanced pages such as:

: [[ROS summary]], dealing with ROS installation/configuration, ROS packages, interaction of ROS with external systems (e.g.: Gazebo, Eclipse)

: [[ROS components]], dealing with specific ROS components (such as tf, the parameter server, rviz...)

= ROS in general =
[http://www.ros.org/wiki/ ROS (Robot Operating System)] is an open-source framework for the creation of software for robots. It is a very interesting tool, since it promises to take care of many of the lower-level issues that make realizing the software for autonomous robots so difficult and time-consuming. By leaving such issues (e.g., communication among modules) to ROS, a researcher can focus on the more interesting high-level issues (e.g., perception).
In the words of [http://www.willowgarage.com/ its creators]:

''"ROS provides libraries and tools to help software developers create robot applications. It provides hardware abstraction, device drivers, libraries, visualizers, message-passing, package management, and more."''

ROS includes a large collection of '''packages''' that you can incorporate into your own system. A ROS package is a bundle of software dedicated to a single functionality (e.g., data acquisition from a laser scanner). Your own ROS-based applications will take the form of one or more ROS packages. If they can be useful to other people as well, once they are completed and tested such packages could become part of ROS: much of ROS was born in this way.

Though striving to be as easy-to-use as possible, ROS is a complex tool. This is unavoidable, as autonomous robots themselves are very complex systems. Before you can start writing your own ROS-based software, you have to devote a fair amount of time to studying how it works and how to use it. This HOWTO will help you to start using ROS as quickly as possible.

== How to get ROS ==
This is probably the single aspect where the ROS team succeeded best in removing all the difficulties, even for beginners. Installing ROS is very simple: [http://www.ros.org/wiki/groovy/Installation this webpage tells you how] (just follow the link dedicated to your Operating System). Please note that the instructions there include permanently setting the appropriate environment variables: you can check that with

: <code>$ export | grep ROS</code>

You ''won't'' need to do that again, so ignore any instructions about this (e.g. about using command ''source'') that subsequent tutorials will give you.

=== Installing additional packages ===
''[Note: this section may be partly obsolete. Starting from ROS version ''Groovy'', [http://www.ros.org/news/2012/12/ros-groovy-galapagos-released.html stacks are no longer used and the basic unit of ROS is the ''package'']. (Yes, there is the new concept of ''metapackage'' that in some ways substitutes that of stacks, but metapackages are indeed packages.)]''

ROS packages are subdivided into groups called '''stacks'''. When you install ROS, not all the stacks are installed. You can see which of them are available on your PC by opening a terminal and running

: <code>rospack profile</code>

Sometimes you need a ROS package that is not installed, i.e. that is not present in any of the installed stacks. For example, let's say that you need the driver for a Hokuyo laser range scanner. The best way to get it is to install the stack that includes the package. To know the name of such stack, you can go to the webpage dedicated to the package in the ROS wiki (so you need to know the name of the package). In our example the package is called ''hokuyo_node'', and its webpage is [http://ros.org/wiki/hokuyo_node this one]. At the top of the package webpage, just under the name of the package, you will find the name of the stack it belongs to (and the name of the other packages of the stack) in the form

: name_of_the_stack: name_of_package_1 / name_of_package_2 ...

In our example, the stack is called ''laser_drivers''.

Now you can install the stack. As we said above, ROS is usually installed using the same tools used for all the other software available for your operating system. To install an additional ROS stack, you will use those same tools. For instance, in Ubuntu Linux you can use Ubuntu Software Center, Synaptic or (from the command-line) apt-get.

Generally the name of the software package corrisponding to a ROS stack is the name of the stack with additional information attached to identify what version of ROS it belongs to. For instance, if your version of ROS is the one called "electric", you will have to look for something called ''ros-electric-laser-drivers''. If you are using apt-get you can install this software package (which, as we said, includes the ROS stack named ''laser_drivers'') with

: <code>sudo apt-get install ros-electric-laser-drivers</code>

(you will be asked for your administrative password).

Finally, sometimes the stack you are looking for is not available as a software package because it's experimental. In this case you can install its source code by following [http://answers.ros.org/question/9201/how-do-i-install-a-missing-ros-package/ these instructions].

=== More about ROS packages ===
There are many other things that can be said about ROS packages, such as what is their internal structure. You can find this information in the AIRWiki page [[ROS summary]].

== How to get information about ROS ==
The [http://www.ros.org/wiki/ '''ROS website'''] includes a good deal of information, structured as a wiki (just like AIRWiki). You are invited to use it heavily, and it's important that you learn to find things in it. That said, not always the information provided by the ROS wiki is very clear for someone who is not an expert in ROS, nor all topics are equally covered.

To make things worse, the ROS wiki distinctly lacks structure. It is basically a collection of pages dedicated to single packages, and little structure or classification information is provided. The result is that, more often than not, even when you are looking for information that is in the wiki you are not able to reach it easily. Usually you have to google for the topic you're interested in, read something here and there on the Internet, try to identify a set of ROS packages that ''could'' be interesting for your problem, and only then you can go to the ROS wiki and look for such packages.
Often you get to interesting wiki pages by chance: i.e., by clicking on a promising link located in a page which only marginally deals with the topic. So... explore!

This page of AIRWiki tries to complement what's provided by the ROS website with additional information, instead of saying the same things in a different way. In a nutshell, this HOWTO is a structured collection of whatever it would have been nice to find in the official documentation about ROS, but wasn't there (or was hidden too well).

=== ROS tutorials ===
ROS includes a rather comprehensive set of tutorials, some of which [http://www.ros.org/wiki/ROS/Tutorials are listed here]. Most tutorials, however, are only accessible from the "Package links" section of the relevant packages: so, unfortunately, you will have to hunt through the ROS wiki to find them.

ROS tutorials are extremely useful, though not always 100% accurate. (E.g.: something does not work as described, or leads to unexpected errors, and you have to work out why for yourself. By doing so you learn a lot, but you also lose a great deal of time.)
The ROS tutorials are subdivided in "difficulty levels". Currently the levels are "basic" and "intermediate". Keep in mind that the tutorials have been written by different people at different times: so don't expect two tutorial of the same "level" to be consistent in what they assume you already know!

Arguably, the most useful tools to learn how to use ROS are the [http://www.ros.org/wiki/ROS/Tutorials basic tutorials]. Be sure to go through them before writing a single line of code (except those that you will write for the tutorial, of course!). Once you have worked your way through the tutorials, the next thing to do is to write your own ROS package and apply what you have learned. The "Nodes" section below is the suggested starting point for that.
Maybe you should start experimenting with a "test" package, before passing to a real application: in this way you can experiment without worrying if the end result is a mess :-) ''You are strongly invited to experiment'': as usually happens in computer programming, that's the best way to understand and check if you have correctly understood, all at the same time.

Before you start with the tutorials, please read this [http://www.ros.org/wiki/ROS/Introduction introduction to the concepts behind ROS]: you will not necessarily understand how things are done in practice until you will have completed the tutorials, but reading it before passing to these will provide you with useful background.

=== Package links ===
As already said, the most common page of the ROS website is the one dedicated to a specific package. It is the starting point to learn everything about that package. One of the most important elements of package pages is the blue rectangle called ''Package Links''. It includes links to many useful resources for users of such package, such as tutorials, FAQ and more.

= ROS features and basic usage =

== Programming languages ==
ROS, ''per se'', does not force the developer to use a specific programming language. In practice, while there are expansion plans for the future, at present only two languages are supported: '''C++''' and '''Python'''. That is to say, only for these two languages ROS provides ''client libraries'' that enable non-ROS software to interface with ROS. Such libraries are called [http://ros.org/wiki/roscpp roscpp] (for C++) and [http://www.ros.org/wiki/rospy rospy] (for Python).

You can choose what language to use on a module-per-module basis, choosing C++ or Python (or whatever other language will be supported in the future) separately for each software module of your ROS system. As we will explain shortly, ROS software modules are called ''nodes''.

Tutorials for roscpp and rospy are available: see [http://www.ros.org/wiki/roscpp_tutorials here] and [http://www.ros.org/wiki/rospy_tutorials here] respectively.

== Measurement units and conventions ==
ROS faces the same problems that any software system which has to deal with physical quantities (to cite but one: position in space!) has to tackle: namely, (i) choice of measurement units and (ii) choice of measurement conventions (e.g., orientation of coordinate systems). Unfortunately, programming languages do not allow physical dimensions or conventions to be attached to data; therefore, these have to be specified outside the software. For ROS, [http://www.ros.org/reps/rep-0103.html units and conventions are specified here].

In particular, ROS measurement units are those of the [http://en.wikipedia.org/wiki/Metric_system Metric System]: metre, kilogram, second, Ampére, radian, Hertz, Newton, Watt, Volt, Celsius.

== Starting and stopping ROS components ==
One powerful feature of ROS is that (provided that roscore is running) you can start or stop any element of ROS (both nodes and debugging tools like rxconsole or rviz) whenever you like: the ROS system will automatically react to the changes and reconfigure itself. (To stop a ROS element you can simply highlight the terminal window where it was launched and press '''Ctrl+C'''.)

In some cases ROS or one of its elements take a few seconds to react to the starting or stopping of a ROS module. In other cases, something just gets stuck and has to be stopped and started again (rxgraph, notably): however, this happens rarely.

= ROS nodes =
The basic element, or module, of a ROS-based software system is the '''node'''. A node executes one or more tasks and communicates with other nodes using the ROS infrastructure. Such communication takes the form of an exchange of '''messages'''. For instance, messages can be used to pass sensor data to a processing node, or to issue commands to a motor-controlling node. Many predefined types of ROS messages are available; if none of them suits your requirements, you can define new message types. A message can include a ''timestamp'', which tells to the recipient when it has been generated: this is especially useful when dealing with sensor data. ROS usually calls "Stamped" a message type that includes a timestamp; this is useful to keep in mind while choosing among available message types.

Communications among modules of a ROS system should always be performed using ROS messages. In fact, the many powerful tools provided by ROS to collect, analyze and debug such communications are all targeted to the processing of messages, and become useless if your system does not use these.

Of course, there are real-world situations when communicating data through messages is not feasible because it would require too many resources. For instance, this happens when a large set of data (such as a complex map) has to be processed by different modules. Using messages to provide the map to each module would require the frequent generation of copies of it (thus wasting both CPU time, for creation, and RAM space, for storage). The typical solution to such problems is to let all the modules involved access the RAM area where the data are stored, thus exchanging only pointers; however, ROS provides its own solutions, which you should investigate first. One of these is the use of [http://www.ros.org/wiki/nodelet nodelets].

A key aspect of the communications among ROS nodes is that, as they are based on the exchange of ROS messages, they are '''asynchronous'''. Outgoing messages are delivered as soon as the ROS system manages to free the necessary resources, are stored in a queue by the receiving node(s), and the node(s) processes them as soon as it is able to (i.e., as soon as it "awakens" if it is executed periodically). An important consequence of this is that ''you must never count on correct message timing, or even on correct ordering, for critical aspects of your system's functioning''. Your ROS system must be tolerant of alterations in the message flow such as delays, misordering, or loss.

Messages that deal with the same aspect of the functioning of the robot can be grouped by publishing them on the same '''topic'''. A topic identifies a "communication channel", shared by nodes that deal with the same aspect of the robot. Each node can ''subscribe'' to the topics it is interested in (thus receiving all the messages that are published on them, without being bothered by messages published on other topics) and/or publish messages on them (thus ensuring that its messages reach all interested nodes).

A node can perform several types of activities, including:

* '''publishing messages on a ROS topic;'''

* '''requesting a service from ROS servers, i.e. acting as a ROS ''client'';'''

* '''acting as a ROS ''server'', i.e. providing services to ROS clients;'''

* '''executing a task whenever a message is published on a ROS topic;'''

* '''managing a timeout and executing a task if it expires;'''

* '''execute a task periodically.'''

These are the activities that are concerned with the interaction between the node and the whole ROS system it is part of. In addition to them, the node can perform internal activities, such as (for instance) data processing. While the ways in which a node interacts with the ROS system are defined by ROS and are based on the use of ROS tools, the internal activities of a node are not constrained by ROS in any way (though of course if they use up too much resources, such as RAM or processing power, they can affect the rest of the system indirectly).

In practice, '''a node is implemented as a single executable file'''. This is produced from a source code file written in one of the programming languages supported by ROS. For instance, if you use C++ you will have to write a .cpp file comprising a main block (and anything else your program needs to work, such as additional functions, data types, #include directives and so on).

== AIRLab's general node template ==
[[Image:ExampleROSTemplate.png |thumb|right|200px|A fragment of the template. Click on the image for a larger view.]]

[ftp://ftp.elet.polimi.it/users/Giulio.Fontana/ROS/general_ROS_node_template.cpp '''AIRLab's general ROS node template'''] provides all the elements that you need to set up the structure of the .cpp file of a basic ROS node. By using the template, you can immediately write a node capable of all the types of activities that a node can perform (as described above).
The template includes a single C++ class comprehending a suitable set of member variables and member functions, plus a very simple ''main'' block. By uncommenting the parts of the template that you require for your ROS node, you can quickly set up the structure of the node. Moreover, the template includes notes and comments that explain how a ROS node is built and works in practice.

== Filenames and node names ==
''[Note: this section is only valid if C++ is used to define nodes. TODO: expand to the Python case.]''

''[Note: this section may be partly obsolete. In fact, starting from ROS version ''Groovy'', [http://www.ros.org/news/2012/12/ros-groovy-galapagos-released.html rosbuild is no more the standard build system for ROS]. It has been substituted with a new system, called [http://www.ros.org/wiki/catkin/conceptual_overview#What_is_a_Build_System.3F ''catkin'']. Some important differences exist between rosbuild and catkin: for instance, [http://www.ros.org/wiki/catkin/conceptual_overview#Differences_in_rosbuild_and_catkin_Build_Step rosmake is no more the standard compile command]. Initially, [http://www.ros.org/wiki/catkin/conceptual_overview#catkin.2BAC8-rosbuild_Compatibility compatibility with rosmake will be retained], though it is now deprecated; but in the long run rosmake will be eliminated. So '''new project must use catkin'''.]''

The .cpp files that define ROS nodes can have any name, provided that such names [http://www.ros.org/wiki/ROS/Concepts#Names.Names are legal].

When a .cpp file is compiled using rosmake, the files that are generated by the compilation process (which include the executables in the /bin subdirectory) take the names that are specified by the CMakeLists.txt file. For instance, putting in CMakeLists.txt the line

: <code>rosbuild_add_executable(name_of_executable src/name_of.cpp)</code>

instructs rosmake to compile file name_of.cpp and call name_of_executable the resulting binary file.

The name of the executable takes the role of the name of ''type of node''. All ROS nodes which are run using such executable are of the same type (i.e., they work in the exact same way) but take different names depending on the way they are run.

If a single instance of such type of node is run with ''rosrun'', it will take as its own name the name of its type; when, instead, one or more instances of such type of node are run with roslaunch, each of them can be given an arbitrary individual name.

When a ROS node is run using rosrun, the running ROS node takes the name specified in the associated .cpp file. Precisely, the .cpp file that defines the node always includes a statement like

: <code>ros::init(argc, argv, "name_of_the_node");</code>

The string between quotes is the name given to the running node.

Usually (for complex ROS systems, at least) nodes are not run with rosrun. ''roslaunch'' is used instead, to perform several operations at the same time (including, but not limited to, running nodes). In this case, the names taken by the running nodes are specified by the .launch file passed to roslaunch. For instance, if file launchfile includes the line

: <code><node pkg="name_of_package" type="name_of_executable" name="name_of_the_node" /></code>

a node called name_of_the_node will be run using the executable name_of_the_executable contained in package name_of_package.

In a running ROS system, each node must have a unique name. If a new node with the same name of one that is already active is run, the older node is stopped by ROS (and a warning is generated). A consequence of this is that you can't run two or more nodes of the same type with rosrun, as only one of them (the last) would remain active. This is a case when running the nodes with roslaunch is a necessity, because you need to assign a different name to each instance of the node.

ROS HOWTO

2016-11-09T09:35:27Z

GiulioFontana: /* ROS in AIRWiki */

= ROS in AIRWiki =
The page you are reading is an introduction to ROS. If you are a ROS beginner, we suggest that you start from it. AIRWiki pages dedicated to ROS users also include more advanced pages such as:

: [[ROS summary]], dealing with ROS installation and configuration, ROS packages and interaction with external systems such as Eclipse or Gazebo

: [[ROS components]], dealing with specific ROS components (such as tf, the parameter server, rviz...)

= ROS in general =
[http://www.ros.org/wiki/ ROS (Robot Operating System)] is an open-source framework for the creation of software for robots. It is a very interesting tool, since it promises to take care of many of the lower-level issues that make realizing the software for autonomous robots so difficult and time-consuming. By leaving such issues (e.g., communication among modules) to ROS, a researcher can focus on the more interesting high-level issues (e.g., perception).
In the words of [http://www.willowgarage.com/ its creators]:

''"ROS provides libraries and tools to help software developers create robot applications. It provides hardware abstraction, device drivers, libraries, visualizers, message-passing, package management, and more."''

ROS includes a large collection of '''packages''' that you can incorporate into your own system. A ROS package is a bundle of software dedicated to a single functionality (e.g., data acquisition from a laser scanner). Your own ROS-based applications will take the form of one or more ROS packages. If they can be useful to other people as well, once they are completed and tested such packages could become part of ROS: much of ROS was born in this way.

Though striving to be as easy-to-use as possible, ROS is a complex tool. This is unavoidable, as autonomous robots themselves are very complex systems. Before you can start writing your own ROS-based software, you have to devote a fair amount of time to studying how it works and how to use it. This HOWTO will help you to start using ROS as quickly as possible.

== How to get ROS ==
This is probably the single aspect where the ROS team succeeded best in removing all the difficulties, even for beginners. Installing ROS is very simple: [http://www.ros.org/wiki/groovy/Installation this webpage tells you how] (just follow the link dedicated to your Operating System). Please note that the instructions there include permanently setting the appropriate environment variables: you can check that with

: <code>$ export | grep ROS</code>

You ''won't'' need to do that again, so ignore any instructions about this (e.g. about using command ''source'') that subsequent tutorials will give you.

=== Installing additional packages ===
''[Note: this section may be partly obsolete. Starting from ROS version ''Groovy'', [http://www.ros.org/news/2012/12/ros-groovy-galapagos-released.html stacks are no longer used and the basic unit of ROS is the ''package'']. (Yes, there is the new concept of ''metapackage'' that in some ways substitutes that of stacks, but metapackages are indeed packages.)]''

ROS packages are subdivided into groups called '''stacks'''. When you install ROS, not all the stacks are installed. You can see which of them are available on your PC by opening a terminal and running

: <code>rospack profile</code>

Sometimes you need a ROS package that is not installed, i.e. that is not present in any of the installed stacks. For example, let's say that you need the driver for a Hokuyo laser range scanner. The best way to get it is to install the stack that includes the package. To know the name of such stack, you can go to the webpage dedicated to the package in the ROS wiki (so you need to know the name of the package). In our example the package is called ''hokuyo_node'', and its webpage is [http://ros.org/wiki/hokuyo_node this one]. At the top of the package webpage, just under the name of the package, you will find the name of the stack it belongs to (and the name of the other packages of the stack) in the form

: name_of_the_stack: name_of_package_1 / name_of_package_2 ...

In our example, the stack is called ''laser_drivers''.

Now you can install the stack. As we said above, ROS is usually installed using the same tools used for all the other software available for your operating system. To install an additional ROS stack, you will use those same tools. For instance, in Ubuntu Linux you can use Ubuntu Software Center, Synaptic or (from the command-line) apt-get.

Generally the name of the software package corrisponding to a ROS stack is the name of the stack with additional information attached to identify what version of ROS it belongs to. For instance, if your version of ROS is the one called "electric", you will have to look for something called ''ros-electric-laser-drivers''. If you are using apt-get you can install this software package (which, as we said, includes the ROS stack named ''laser_drivers'') with

: <code>sudo apt-get install ros-electric-laser-drivers</code>

(you will be asked for your administrative password).

Finally, sometimes the stack you are looking for is not available as a software package because it's experimental. In this case you can install its source code by following [http://answers.ros.org/question/9201/how-do-i-install-a-missing-ros-package/ these instructions].

=== More about ROS packages ===
There are many other things that can be said about ROS packages, such as what is their internal structure. You can find this information in the AIRWiki page [[ROS summary]].

== How to get information about ROS ==
The [http://www.ros.org/wiki/ '''ROS website'''] includes a good deal of information, structured as a wiki (just like AIRWiki). You are invited to use it heavily, and it's important that you learn to find things in it. That said, not always the information provided by the ROS wiki is very clear for someone who is not an expert in ROS, nor all topics are equally covered.

To make things worse, the ROS wiki distinctly lacks structure. It is basically a collection of pages dedicated to single packages, and little structure or classification information is provided. The result is that, more often than not, even when you are looking for information that is in the wiki you are not able to reach it easily. Usually you have to google for the topic you're interested in, read something here and there on the Internet, try to identify a set of ROS packages that ''could'' be interesting for your problem, and only then you can go to the ROS wiki and look for such packages.
Often you get to interesting wiki pages by chance: i.e., by clicking on a promising link located in a page which only marginally deals with the topic. So... explore!

This page of AIRWiki tries to complement what's provided by the ROS website with additional information, instead of saying the same things in a different way. In a nutshell, this HOWTO is a structured collection of whatever it would have been nice to find in the official documentation about ROS, but wasn't there (or was hidden too well).

=== ROS tutorials ===
ROS includes a rather comprehensive set of tutorials, some of which [http://www.ros.org/wiki/ROS/Tutorials are listed here]. Most tutorials, however, are only accessible from the "Package links" section of the relevant packages: so, unfortunately, you will have to hunt through the ROS wiki to find them.

ROS tutorials are extremely useful, though not always 100% accurate. (E.g.: something does not work as described, or leads to unexpected errors, and you have to work out why for yourself. By doing so you learn a lot, but you also lose a great deal of time.)
The ROS tutorials are subdivided in "difficulty levels". Currently the levels are "basic" and "intermediate". Keep in mind that the tutorials have been written by different people at different times: so don't expect two tutorial of the same "level" to be consistent in what they assume you already know!

Arguably, the most useful tools to learn how to use ROS are the [http://www.ros.org/wiki/ROS/Tutorials basic tutorials]. Be sure to go through them before writing a single line of code (except those that you will write for the tutorial, of course!). Once you have worked your way through the tutorials, the next thing to do is to write your own ROS package and apply what you have learned. The "Nodes" section below is the suggested starting point for that.
Maybe you should start experimenting with a "test" package, before passing to a real application: in this way you can experiment without worrying if the end result is a mess :-) ''You are strongly invited to experiment'': as usually happens in computer programming, that's the best way to understand and check if you have correctly understood, all at the same time.

Before you start with the tutorials, please read this [http://www.ros.org/wiki/ROS/Introduction introduction to the concepts behind ROS]: you will not necessarily understand how things are done in practice until you will have completed the tutorials, but reading it before passing to these will provide you with useful background.

=== Package links ===
As already said, the most common page of the ROS website is the one dedicated to a specific package. It is the starting point to learn everything about that package. One of the most important elements of package pages is the blue rectangle called ''Package Links''. It includes links to many useful resources for users of such package, such as tutorials, FAQ and more.

= ROS features and basic usage =

== Programming languages ==
ROS, ''per se'', does not force the developer to use a specific programming language. In practice, while there are expansion plans for the future, at present only two languages are supported: '''C++''' and '''Python'''. That is to say, only for these two languages ROS provides ''client libraries'' that enable non-ROS software to interface with ROS. Such libraries are called [http://ros.org/wiki/roscpp roscpp] (for C++) and [http://www.ros.org/wiki/rospy rospy] (for Python).

You can choose what language to use on a module-per-module basis, choosing C++ or Python (or whatever other language will be supported in the future) separately for each software module of your ROS system. As we will explain shortly, ROS software modules are called ''nodes''.

Tutorials for roscpp and rospy are available: see [http://www.ros.org/wiki/roscpp_tutorials here] and [http://www.ros.org/wiki/rospy_tutorials here] respectively.

== Measurement units and conventions ==
ROS faces the same problems that any software system which has to deal with physical quantities (to cite but one: position in space!) has to tackle: namely, (i) choice of measurement units and (ii) choice of measurement conventions (e.g., orientation of coordinate systems). Unfortunately, programming languages do not allow physical dimensions or conventions to be attached to data; therefore, these have to be specified outside the software. For ROS, [http://www.ros.org/reps/rep-0103.html units and conventions are specified here].

In particular, ROS measurement units are those of the [http://en.wikipedia.org/wiki/Metric_system Metric System]: metre, kilogram, second, Ampére, radian, Hertz, Newton, Watt, Volt, Celsius.

== Starting and stopping ROS components ==
One powerful feature of ROS is that (provided that roscore is running) you can start or stop any element of ROS (both nodes and debugging tools like rxconsole or rviz) whenever you like: the ROS system will automatically react to the changes and reconfigure itself. (To stop a ROS element you can simply highlight the terminal window where it was launched and press '''Ctrl+C'''.)

In some cases ROS or one of its elements take a few seconds to react to the starting or stopping of a ROS module. In other cases, something just gets stuck and has to be stopped and started again (rxgraph, notably): however, this happens rarely.

= ROS nodes =
The basic element, or module, of a ROS-based software system is the '''node'''. A node executes one or more tasks and communicates with other nodes using the ROS infrastructure. Such communication takes the form of an exchange of '''messages'''. For instance, messages can be used to pass sensor data to a processing node, or to issue commands to a motor-controlling node. Many predefined types of ROS messages are available; if none of them suits your requirements, you can define new message types. A message can include a ''timestamp'', which tells to the recipient when it has been generated: this is especially useful when dealing with sensor data. ROS usually calls "Stamped" a message type that includes a timestamp; this is useful to keep in mind while choosing among available message types.

Communications among modules of a ROS system should always be performed using ROS messages. In fact, the many powerful tools provided by ROS to collect, analyze and debug such communications are all targeted to the processing of messages, and become useless if your system does not use these.

Of course, there are real-world situations when communicating data through messages is not feasible because it would require too many resources. For instance, this happens when a large set of data (such as a complex map) has to be processed by different modules. Using messages to provide the map to each module would require the frequent generation of copies of it (thus wasting both CPU time, for creation, and RAM space, for storage). The typical solution to such problems is to let all the modules involved access the RAM area where the data are stored, thus exchanging only pointers; however, ROS provides its own solutions, which you should investigate first. One of these is the use of [http://www.ros.org/wiki/nodelet nodelets].

A key aspect of the communications among ROS nodes is that, as they are based on the exchange of ROS messages, they are '''asynchronous'''. Outgoing messages are delivered as soon as the ROS system manages to free the necessary resources, are stored in a queue by the receiving node(s), and the node(s) processes them as soon as it is able to (i.e., as soon as it "awakens" if it is executed periodically). An important consequence of this is that ''you must never count on correct message timing, or even on correct ordering, for critical aspects of your system's functioning''. Your ROS system must be tolerant of alterations in the message flow such as delays, misordering, or loss.

Messages that deal with the same aspect of the functioning of the robot can be grouped by publishing them on the same '''topic'''. A topic identifies a "communication channel", shared by nodes that deal with the same aspect of the robot. Each node can ''subscribe'' to the topics it is interested in (thus receiving all the messages that are published on them, without being bothered by messages published on other topics) and/or publish messages on them (thus ensuring that its messages reach all interested nodes).

A node can perform several types of activities, including:

* '''publishing messages on a ROS topic;'''

* '''requesting a service from ROS servers, i.e. acting as a ROS ''client'';'''

* '''acting as a ROS ''server'', i.e. providing services to ROS clients;'''

* '''executing a task whenever a message is published on a ROS topic;'''

* '''managing a timeout and executing a task if it expires;'''

* '''execute a task periodically.'''

These are the activities that are concerned with the interaction between the node and the whole ROS system it is part of. In addition to them, the node can perform internal activities, such as (for instance) data processing. While the ways in which a node interacts with the ROS system are defined by ROS and are based on the use of ROS tools, the internal activities of a node are not constrained by ROS in any way (though of course if they use up too much resources, such as RAM or processing power, they can affect the rest of the system indirectly).

In practice, '''a node is implemented as a single executable file'''. This is produced from a source code file written in one of the programming languages supported by ROS. For instance, if you use C++ you will have to write a .cpp file comprising a main block (and anything else your program needs to work, such as additional functions, data types, #include directives and so on).

== AIRLab's general node template ==
[[Image:ExampleROSTemplate.png |thumb|right|200px|A fragment of the template. Click on the image for a larger view.]]

[ftp://ftp.elet.polimi.it/users/Giulio.Fontana/ROS/general_ROS_node_template.cpp '''AIRLab's general ROS node template'''] provides all the elements that you need to set up the structure of the .cpp file of a basic ROS node. By using the template, you can immediately write a node capable of all the types of activities that a node can perform (as described above).
The template includes a single C++ class comprehending a suitable set of member variables and member functions, plus a very simple ''main'' block. By uncommenting the parts of the template that you require for your ROS node, you can quickly set up the structure of the node. Moreover, the template includes notes and comments that explain how a ROS node is built and works in practice.

== Filenames and node names ==
''[Note: this section is only valid if C++ is used to define nodes. TODO: expand to the Python case.]''

''[Note: this section may be partly obsolete. In fact, starting from ROS version ''Groovy'', [http://www.ros.org/news/2012/12/ros-groovy-galapagos-released.html rosbuild is no more the standard build system for ROS]. It has been substituted with a new system, called [http://www.ros.org/wiki/catkin/conceptual_overview#What_is_a_Build_System.3F ''catkin'']. Some important differences exist between rosbuild and catkin: for instance, [http://www.ros.org/wiki/catkin/conceptual_overview#Differences_in_rosbuild_and_catkin_Build_Step rosmake is no more the standard compile command]. Initially, [http://www.ros.org/wiki/catkin/conceptual_overview#catkin.2BAC8-rosbuild_Compatibility compatibility with rosmake will be retained], though it is now deprecated; but in the long run rosmake will be eliminated. So '''new project must use catkin'''.]''

The .cpp files that define ROS nodes can have any name, provided that such names [http://www.ros.org/wiki/ROS/Concepts#Names.Names are legal].

When a .cpp file is compiled using rosmake, the files that are generated by the compilation process (which include the executables in the /bin subdirectory) take the names that are specified by the CMakeLists.txt file. For instance, putting in CMakeLists.txt the line

: <code>rosbuild_add_executable(name_of_executable src/name_of.cpp)</code>

instructs rosmake to compile file name_of.cpp and call name_of_executable the resulting binary file.

The name of the executable takes the role of the name of ''type of node''. All ROS nodes which are run using such executable are of the same type (i.e., they work in the exact same way) but take different names depending on the way they are run.

If a single instance of such type of node is run with ''rosrun'', it will take as its own name the name of its type; when, instead, one or more instances of such type of node are run with roslaunch, each of them can be given an arbitrary individual name.

When a ROS node is run using rosrun, the running ROS node takes the name specified in the associated .cpp file. Precisely, the .cpp file that defines the node always includes a statement like

: <code>ros::init(argc, argv, "name_of_the_node");</code>

The string between quotes is the name given to the running node.

Usually (for complex ROS systems, at least) nodes are not run with rosrun. ''roslaunch'' is used instead, to perform several operations at the same time (including, but not limited to, running nodes). In this case, the names taken by the running nodes are specified by the .launch file passed to roslaunch. For instance, if file launchfile includes the line

: <code><node pkg="name_of_package" type="name_of_executable" name="name_of_the_node" /></code>

a node called name_of_the_node will be run using the executable name_of_the_executable contained in package name_of_package.

In a running ROS system, each node must have a unique name. If a new node with the same name of one that is already active is run, the older node is stopped by ROS (and a warning is generated). A consequence of this is that you can't run two or more nodes of the same type with rosrun, as only one of them (the last) would remain active. This is a case when running the nodes with roslaunch is a necessity, because you need to assign a different name to each instance of the node.

ROS HOWTO

2016-11-09T09:35:08Z

GiulioFontana:

= ROS in AIRWiki =
The page you are reading is an introduction to ROS. If you are a ROS beginner, we suggest that you start from it. AIRWiki pages dedicated to ROS users also include more advanced pages such as:

[[ROS summary]], dealing with ROS installation and configuration, ROS packages and interaction with external systems such as Eclipse or Gazebo

[[ROS components]], dealing with specific ROS components (such as tf, the parameter server, rviz...)

= ROS in general =
[http://www.ros.org/wiki/ ROS (Robot Operating System)] is an open-source framework for the creation of software for robots. It is a very interesting tool, since it promises to take care of many of the lower-level issues that make realizing the software for autonomous robots so difficult and time-consuming. By leaving such issues (e.g., communication among modules) to ROS, a researcher can focus on the more interesting high-level issues (e.g., perception).
In the words of [http://www.willowgarage.com/ its creators]:

''"ROS provides libraries and tools to help software developers create robot applications. It provides hardware abstraction, device drivers, libraries, visualizers, message-passing, package management, and more."''

ROS includes a large collection of '''packages''' that you can incorporate into your own system. A ROS package is a bundle of software dedicated to a single functionality (e.g., data acquisition from a laser scanner). Your own ROS-based applications will take the form of one or more ROS packages. If they can be useful to other people as well, once they are completed and tested such packages could become part of ROS: much of ROS was born in this way.

Though striving to be as easy-to-use as possible, ROS is a complex tool. This is unavoidable, as autonomous robots themselves are very complex systems. Before you can start writing your own ROS-based software, you have to devote a fair amount of time to studying how it works and how to use it. This HOWTO will help you to start using ROS as quickly as possible.

== How to get ROS ==
This is probably the single aspect where the ROS team succeeded best in removing all the difficulties, even for beginners. Installing ROS is very simple: [http://www.ros.org/wiki/groovy/Installation this webpage tells you how] (just follow the link dedicated to your Operating System). Please note that the instructions there include permanently setting the appropriate environment variables: you can check that with

: <code>$ export | grep ROS</code>

You ''won't'' need to do that again, so ignore any instructions about this (e.g. about using command ''source'') that subsequent tutorials will give you.

=== Installing additional packages ===
''[Note: this section may be partly obsolete. Starting from ROS version ''Groovy'', [http://www.ros.org/news/2012/12/ros-groovy-galapagos-released.html stacks are no longer used and the basic unit of ROS is the ''package'']. (Yes, there is the new concept of ''metapackage'' that in some ways substitutes that of stacks, but metapackages are indeed packages.)]''

ROS packages are subdivided into groups called '''stacks'''. When you install ROS, not all the stacks are installed. You can see which of them are available on your PC by opening a terminal and running

: <code>rospack profile</code>

Sometimes you need a ROS package that is not installed, i.e. that is not present in any of the installed stacks. For example, let's say that you need the driver for a Hokuyo laser range scanner. The best way to get it is to install the stack that includes the package. To know the name of such stack, you can go to the webpage dedicated to the package in the ROS wiki (so you need to know the name of the package). In our example the package is called ''hokuyo_node'', and its webpage is [http://ros.org/wiki/hokuyo_node this one]. At the top of the package webpage, just under the name of the package, you will find the name of the stack it belongs to (and the name of the other packages of the stack) in the form

: name_of_the_stack: name_of_package_1 / name_of_package_2 ...

In our example, the stack is called ''laser_drivers''.

Now you can install the stack. As we said above, ROS is usually installed using the same tools used for all the other software available for your operating system. To install an additional ROS stack, you will use those same tools. For instance, in Ubuntu Linux you can use Ubuntu Software Center, Synaptic or (from the command-line) apt-get.

Generally the name of the software package corrisponding to a ROS stack is the name of the stack with additional information attached to identify what version of ROS it belongs to. For instance, if your version of ROS is the one called "electric", you will have to look for something called ''ros-electric-laser-drivers''. If you are using apt-get you can install this software package (which, as we said, includes the ROS stack named ''laser_drivers'') with

: <code>sudo apt-get install ros-electric-laser-drivers</code>

(you will be asked for your administrative password).

Finally, sometimes the stack you are looking for is not available as a software package because it's experimental. In this case you can install its source code by following [http://answers.ros.org/question/9201/how-do-i-install-a-missing-ros-package/ these instructions].

=== More about ROS packages ===
There are many other things that can be said about ROS packages, such as what is their internal structure. You can find this information in the AIRWiki page [[ROS summary]].

== How to get information about ROS ==
The [http://www.ros.org/wiki/ '''ROS website'''] includes a good deal of information, structured as a wiki (just like AIRWiki). You are invited to use it heavily, and it's important that you learn to find things in it. That said, not always the information provided by the ROS wiki is very clear for someone who is not an expert in ROS, nor all topics are equally covered.

To make things worse, the ROS wiki distinctly lacks structure. It is basically a collection of pages dedicated to single packages, and little structure or classification information is provided. The result is that, more often than not, even when you are looking for information that is in the wiki you are not able to reach it easily. Usually you have to google for the topic you're interested in, read something here and there on the Internet, try to identify a set of ROS packages that ''could'' be interesting for your problem, and only then you can go to the ROS wiki and look for such packages.
Often you get to interesting wiki pages by chance: i.e., by clicking on a promising link located in a page which only marginally deals with the topic. So... explore!

This page of AIRWiki tries to complement what's provided by the ROS website with additional information, instead of saying the same things in a different way. In a nutshell, this HOWTO is a structured collection of whatever it would have been nice to find in the official documentation about ROS, but wasn't there (or was hidden too well).

=== ROS tutorials ===
ROS includes a rather comprehensive set of tutorials, some of which [http://www.ros.org/wiki/ROS/Tutorials are listed here]. Most tutorials, however, are only accessible from the "Package links" section of the relevant packages: so, unfortunately, you will have to hunt through the ROS wiki to find them.

ROS tutorials are extremely useful, though not always 100% accurate. (E.g.: something does not work as described, or leads to unexpected errors, and you have to work out why for yourself. By doing so you learn a lot, but you also lose a great deal of time.)
The ROS tutorials are subdivided in "difficulty levels". Currently the levels are "basic" and "intermediate". Keep in mind that the tutorials have been written by different people at different times: so don't expect two tutorial of the same "level" to be consistent in what they assume you already know!

Arguably, the most useful tools to learn how to use ROS are the [http://www.ros.org/wiki/ROS/Tutorials basic tutorials]. Be sure to go through them before writing a single line of code (except those that you will write for the tutorial, of course!). Once you have worked your way through the tutorials, the next thing to do is to write your own ROS package and apply what you have learned. The "Nodes" section below is the suggested starting point for that.
Maybe you should start experimenting with a "test" package, before passing to a real application: in this way you can experiment without worrying if the end result is a mess :-) ''You are strongly invited to experiment'': as usually happens in computer programming, that's the best way to understand and check if you have correctly understood, all at the same time.

Before you start with the tutorials, please read this [http://www.ros.org/wiki/ROS/Introduction introduction to the concepts behind ROS]: you will not necessarily understand how things are done in practice until you will have completed the tutorials, but reading it before passing to these will provide you with useful background.

=== Package links ===
As already said, the most common page of the ROS website is the one dedicated to a specific package. It is the starting point to learn everything about that package. One of the most important elements of package pages is the blue rectangle called ''Package Links''. It includes links to many useful resources for users of such package, such as tutorials, FAQ and more.

= ROS features and basic usage =

== Programming languages ==
ROS, ''per se'', does not force the developer to use a specific programming language. In practice, while there are expansion plans for the future, at present only two languages are supported: '''C++''' and '''Python'''. That is to say, only for these two languages ROS provides ''client libraries'' that enable non-ROS software to interface with ROS. Such libraries are called [http://ros.org/wiki/roscpp roscpp] (for C++) and [http://www.ros.org/wiki/rospy rospy] (for Python).

You can choose what language to use on a module-per-module basis, choosing C++ or Python (or whatever other language will be supported in the future) separately for each software module of your ROS system. As we will explain shortly, ROS software modules are called ''nodes''.

Tutorials for roscpp and rospy are available: see [http://www.ros.org/wiki/roscpp_tutorials here] and [http://www.ros.org/wiki/rospy_tutorials here] respectively.

== Measurement units and conventions ==
ROS faces the same problems that any software system which has to deal with physical quantities (to cite but one: position in space!) has to tackle: namely, (i) choice of measurement units and (ii) choice of measurement conventions (e.g., orientation of coordinate systems). Unfortunately, programming languages do not allow physical dimensions or conventions to be attached to data; therefore, these have to be specified outside the software. For ROS, [http://www.ros.org/reps/rep-0103.html units and conventions are specified here].

In particular, ROS measurement units are those of the [http://en.wikipedia.org/wiki/Metric_system Metric System]: metre, kilogram, second, Ampére, radian, Hertz, Newton, Watt, Volt, Celsius.

== Starting and stopping ROS components ==
One powerful feature of ROS is that (provided that roscore is running) you can start or stop any element of ROS (both nodes and debugging tools like rxconsole or rviz) whenever you like: the ROS system will automatically react to the changes and reconfigure itself. (To stop a ROS element you can simply highlight the terminal window where it was launched and press '''Ctrl+C'''.)

In some cases ROS or one of its elements take a few seconds to react to the starting or stopping of a ROS module. In other cases, something just gets stuck and has to be stopped and started again (rxgraph, notably): however, this happens rarely.

= ROS nodes =
The basic element, or module, of a ROS-based software system is the '''node'''. A node executes one or more tasks and communicates with other nodes using the ROS infrastructure. Such communication takes the form of an exchange of '''messages'''. For instance, messages can be used to pass sensor data to a processing node, or to issue commands to a motor-controlling node. Many predefined types of ROS messages are available; if none of them suits your requirements, you can define new message types. A message can include a ''timestamp'', which tells to the recipient when it has been generated: this is especially useful when dealing with sensor data. ROS usually calls "Stamped" a message type that includes a timestamp; this is useful to keep in mind while choosing among available message types.

Communications among modules of a ROS system should always be performed using ROS messages. In fact, the many powerful tools provided by ROS to collect, analyze and debug such communications are all targeted to the processing of messages, and become useless if your system does not use these.

Of course, there are real-world situations when communicating data through messages is not feasible because it would require too many resources. For instance, this happens when a large set of data (such as a complex map) has to be processed by different modules. Using messages to provide the map to each module would require the frequent generation of copies of it (thus wasting both CPU time, for creation, and RAM space, for storage). The typical solution to such problems is to let all the modules involved access the RAM area where the data are stored, thus exchanging only pointers; however, ROS provides its own solutions, which you should investigate first. One of these is the use of [http://www.ros.org/wiki/nodelet nodelets].

A key aspect of the communications among ROS nodes is that, as they are based on the exchange of ROS messages, they are '''asynchronous'''. Outgoing messages are delivered as soon as the ROS system manages to free the necessary resources, are stored in a queue by the receiving node(s), and the node(s) processes them as soon as it is able to (i.e., as soon as it "awakens" if it is executed periodically). An important consequence of this is that ''you must never count on correct message timing, or even on correct ordering, for critical aspects of your system's functioning''. Your ROS system must be tolerant of alterations in the message flow such as delays, misordering, or loss.

Messages that deal with the same aspect of the functioning of the robot can be grouped by publishing them on the same '''topic'''. A topic identifies a "communication channel", shared by nodes that deal with the same aspect of the robot. Each node can ''subscribe'' to the topics it is interested in (thus receiving all the messages that are published on them, without being bothered by messages published on other topics) and/or publish messages on them (thus ensuring that its messages reach all interested nodes).

A node can perform several types of activities, including:

* '''publishing messages on a ROS topic;'''

* '''requesting a service from ROS servers, i.e. acting as a ROS ''client'';'''

* '''acting as a ROS ''server'', i.e. providing services to ROS clients;'''

* '''executing a task whenever a message is published on a ROS topic;'''

* '''managing a timeout and executing a task if it expires;'''

* '''execute a task periodically.'''

These are the activities that are concerned with the interaction between the node and the whole ROS system it is part of. In addition to them, the node can perform internal activities, such as (for instance) data processing. While the ways in which a node interacts with the ROS system are defined by ROS and are based on the use of ROS tools, the internal activities of a node are not constrained by ROS in any way (though of course if they use up too much resources, such as RAM or processing power, they can affect the rest of the system indirectly).

In practice, '''a node is implemented as a single executable file'''. This is produced from a source code file written in one of the programming languages supported by ROS. For instance, if you use C++ you will have to write a .cpp file comprising a main block (and anything else your program needs to work, such as additional functions, data types, #include directives and so on).

== AIRLab's general node template ==
[[Image:ExampleROSTemplate.png |thumb|right|200px|A fragment of the template. Click on the image for a larger view.]]

[ftp://ftp.elet.polimi.it/users/Giulio.Fontana/ROS/general_ROS_node_template.cpp '''AIRLab's general ROS node template'''] provides all the elements that you need to set up the structure of the .cpp file of a basic ROS node. By using the template, you can immediately write a node capable of all the types of activities that a node can perform (as described above).
The template includes a single C++ class comprehending a suitable set of member variables and member functions, plus a very simple ''main'' block. By uncommenting the parts of the template that you require for your ROS node, you can quickly set up the structure of the node. Moreover, the template includes notes and comments that explain how a ROS node is built and works in practice.

== Filenames and node names ==
''[Note: this section is only valid if C++ is used to define nodes. TODO: expand to the Python case.]''

''[Note: this section may be partly obsolete. In fact, starting from ROS version ''Groovy'', [http://www.ros.org/news/2012/12/ros-groovy-galapagos-released.html rosbuild is no more the standard build system for ROS]. It has been substituted with a new system, called [http://www.ros.org/wiki/catkin/conceptual_overview#What_is_a_Build_System.3F ''catkin'']. Some important differences exist between rosbuild and catkin: for instance, [http://www.ros.org/wiki/catkin/conceptual_overview#Differences_in_rosbuild_and_catkin_Build_Step rosmake is no more the standard compile command]. Initially, [http://www.ros.org/wiki/catkin/conceptual_overview#catkin.2BAC8-rosbuild_Compatibility compatibility with rosmake will be retained], though it is now deprecated; but in the long run rosmake will be eliminated. So '''new project must use catkin'''.]''

The .cpp files that define ROS nodes can have any name, provided that such names [http://www.ros.org/wiki/ROS/Concepts#Names.Names are legal].

When a .cpp file is compiled using rosmake, the files that are generated by the compilation process (which include the executables in the /bin subdirectory) take the names that are specified by the CMakeLists.txt file. For instance, putting in CMakeLists.txt the line

: <code>rosbuild_add_executable(name_of_executable src/name_of.cpp)</code>

instructs rosmake to compile file name_of.cpp and call name_of_executable the resulting binary file.

The name of the executable takes the role of the name of ''type of node''. All ROS nodes which are run using such executable are of the same type (i.e., they work in the exact same way) but take different names depending on the way they are run.

If a single instance of such type of node is run with ''rosrun'', it will take as its own name the name of its type; when, instead, one or more instances of such type of node are run with roslaunch, each of them can be given an arbitrary individual name.

When a ROS node is run using rosrun, the running ROS node takes the name specified in the associated .cpp file. Precisely, the .cpp file that defines the node always includes a statement like

: <code>ros::init(argc, argv, "name_of_the_node");</code>

The string between quotes is the name given to the running node.

Usually (for complex ROS systems, at least) nodes are not run with rosrun. ''roslaunch'' is used instead, to perform several operations at the same time (including, but not limited to, running nodes). In this case, the names taken by the running nodes are specified by the .launch file passed to roslaunch. For instance, if file launchfile includes the line

: <code><node pkg="name_of_package" type="name_of_executable" name="name_of_the_node" /></code>

a node called name_of_the_node will be run using the executable name_of_the_executable contained in package name_of_package.

In a running ROS system, each node must have a unique name. If a new node with the same name of one that is already active is run, the older node is stopped by ROS (and a warning is generated). A consequence of this is that you can't run two or more nodes of the same type with rosrun, as only one of them (the last) would remain active. This is a case when running the nodes with roslaunch is a necessity, because you need to assign a different name to each instance of the node.