ROS components - Revision history

GiulioFontana at 10:28, 9 November 2016

2016-11-09T10:28:15Z

GiulioFontana at 10:27, 9 November 2016

2016-11-09T10:27:38Z

GiulioFontana at 10:23, 9 November 2016

2016-11-09T10:23:45Z

GiulioFontana at 09:57, 9 November 2016

2016-11-09T09:57:10Z

GiulioFontana: /* "Stale" transforms? */

2016-11-09T09:55:58Z

‎"Stale" transforms?

GiulioFontana at 09:55, 9 November 2016

2016-11-09T09:55:07Z

GiulioFontana at 09:51, 9 November 2016

2016-11-09T09:51:55Z

GiulioFontana at 09:51, 9 November 2016

2016-11-09T09:51:05Z

GiulioFontana: /* rosbag */

2016-11-09T09:48:33Z

‎rosbag

GiulioFontana at 09:43, 9 November 2016

2016-11-09T09:43:27Z

@@ Line 2: / Line 2: @@
 The page you are reading provides additional information about systems that are an integral part of ROS or that are frequently needed when running or developing a ROS system. Such systems include pieces of the ROS infrastructure (e.g., the parameter server), key ROS packages (e.g., tf) and useful ROS tools (e.g., rosbag, rviz).
-General-purpose information about ROS and its basic elements is available in the [[ROS HOWTO]] page.
+Basic information about ROS and its elements is available in the [[ROS HOWTO]] page. Such page also includes links to other AIRWiki pages related to ROS.
 Such page also includes links to other AIRWiki pages related to ROS.
 = ROS parameter server =

@@ Line 1: / Line 1: @@
-This page provides additional information about systems that are an integral part of ROS or that are frequently needed when running or developing a ROS system. Such systems include pieces of the ROS infrastructure (e.g., the parameter server), key ROS packages (e.g., tf) and useful ROS tools (e.g., rosbag, rviz).
+= ROS in AIRWiki =
 General-purpose information about ROS and its basic elements is available in the [[ROS HOWTO]] page.
 = ROS parameter server =

@@ Line 3: / Line 3: @@
 General-purpose information about ROS and its basic elements is available in the [[ROS HOWTO]] page.
-== ROS parameter server ==
+= ROS parameter server =
 ROS includes a [http://www.ros.org/wiki/Parameter%20Server parameter server] that can be used to store in a centralized way all the configuration parameters of a robot system. As autonomous robots are generally a collection of hetereogeneous modules, each having its own parameters and its own methods for storing and retrieving them, this is a valuable step towards making robot software more easy to use, organized and reusable. Configuration parameters managed by the ROS parameter server are specified using the [http://www.ros.org/wiki/rosparam YAML language]. They can be stored, modified and retrieved at runtime both from the command line and (more importantly) from ROS nodes.
@@ Line 47: / Line 47: @@
 <code>rosparam get /full/name/of/the/param</code>
-== tf ==
+= tf =
 From the [http://www.ros.org/wiki/tf the ROS wiki]: "''tf is a package that lets the user keep track of multiple coordinate frames over time. tf maintains the relationship between coordinate frames in a tree structure buffered in time, and lets the user transform points, vectors, etc between any two coordinate frames at any desired point in time''". [http://wiki.ros.org/tf tf] is a key element of ROS and, if you work on mobile robotics, there's not much that you can do with ROS before you discover that you need tf.
@@ Line 53: / Line 53: @@
 [http://www.ros.org/wiki/navigation/Tutorials/RobotSetup/TF Here is a nice tutorial] about how to use tf.
-=== Transform tree ===
+== Transform tree ==
 Many ROS packages assume that in your ROS system a correct ''transform tree'' has been set up. This means that there are some coordinate systems, and some relations among them, that most ROS packages assume to exist. One of the things that are badly documented in ROS is precisely what these coordinate systems are, and how they relate to each other. Although it's well hidden in the documentation, ROS does define a [http://www.ros.org/reps/rep-0105.html quasi-standard transform tree for ROS], which looks like this:
@@ Line 88: / Line 88: @@
 Tip: to publish fixed transforms you can use the handy [http://www.ros.org/wiki/tf#static_transform_publisher static_transform_publisher].
-=== Who defines ''/world'' or ''/map''? ===
+== Who defines ''/world'' or ''/map''? ==
 One puzzling aspect of the ROS documentation is that it contains countless references to coordinate frames called ''/world'' or ''/map'', which do not seem to be defined anywhere. The solution to this problem is simply that the ''/world' or ''/map'' coordinate frame is defined implicitly. In fact, in any ROS applications where tf is employed, a "default" coordinate frame is used as the starting point to define (through suitable transforms) all the coordinate frames used in the system. Such "default" frame, considered fixed, is called ''/map'', or sometimes ''/world''.
@@ Line 99: / Line 99: @@
 The above statement creates a static_transform_publisher node that every 100ms broadcasts (on the /tf topic) a message specifying that the transform from ''/world'' to ''/map'' has zero translation and zero rotation. (By the way, that value of 100ms comes from the ROS wiki, which says it's a "good value".)
-== rviz ==
+= rviz =
 [http://wiki.ros.org/rviz rviz] is an extremely handy visualizer for data transmitted on ROS topics. It lets the user quickly set up visualizations for most types of ROS messages, including tf transforms, laser data, point clouds, maps, and so on.
@@ Line 109: / Line 109: @@
 * Set in the ''Global Options'' menu the desired ''Fixed Frame'' (typically <code> /map </code>)
-== rosbag ==
+= rosbag =
 [http://wiki.ros.org/rosbag rosbag] is an extremely useful tool to record on file the messages published on ROS topics. You can also use rosbag to "play back" at a later time such messages: for instance, to inspect their content with rviz.
-=== "Stale" transforms? ===
+== "Stale" transforms? ==
 Some ROS tutorials make use of bagfiles containing sensor data and transforms. If you try to play a bagfile with <code>rosbag play</code> and do something with its contents (e.g., visualize the data using rviz), you can get nasty but obscure errors like this:

@@ Line 1: / Line 1: @@
 This page provides additional information about systems that are an integral part of ROS or that are frequently needed when running or developing a ROS system. Such systems include pieces of the ROS infrastructure (e.g., the parameter server), key ROS packages (e.g., tf) and useful ROS tools (e.g., rosbag, rviz).
-General-purpose information about ROS and its basic elements is available in the ROS HOWTO page.
+General-purpose information about ROS and its basic elements is available in the [[ROS HOWTO]] page.
 == ROS parameter server ==

@@ Line 121: / Line 121: @@
 Depending on what ROS tools you are using, the error message can change; but the point is that data have been discarded ''because the transforms between reference frames in the bagfile are too old to be considered reliable''. For instance in rviz you will get something like "ignoring data from the past for frame name_of_the_reference_frame".
-The solution is to force ROS to use ''the time when the bagfile was prepared'' instead of the current time: i.e., to get the time from the bagfile instead of getting it from the "wall clock" (i.e., from your computer's clock). This is done by setting to ''true'' the ROS parameter called ''use_sim_time'', stored by the parameter server. See [[ROS_components#ROS_parameter_server the section about the ROS parameter server]] to read how you can do this.
+The solution is to force ROS to use ''the time when the bagfile was prepared'' instead of the current time: i.e., to get the time from the bagfile instead of getting it from the "wall clock" (i.e., from your computer's clock). This is done by setting to ''true'' the ROS parameter called ''use_sim_time'', stored by the parameter server. See [[ROS_components#ROS_parameter_server|the section about the ROS parameter server]] to read how you can do this.
 After you have set the parameter, you have to run rosbag like this:

@@ Line 69: / Line 69: @@
 Warning: setting ''use_sim_time'' to ''true'' is something that you will only have to do while testing or debugging your system: it should not be done when ROS is used on running robots.
-== tf ==
+== the ''tf'' ROS package ==
 From the [http://www.ros.org/wiki/tf the ROS wiki]: "''tf is a package that lets the user keep track of multiple coordinate frames over time. tf maintains the relationship between coordinate frames in a tree structure buffered in time, and lets the user transform points, vectors, etc between any two coordinate frames at any desired point in time''". [http://wiki.ros.org/tf tf] is a key element of ROS and, if you work on mobile robotics, there's not much that you can do with ROS before you discover that you need tf.

@@ Line 48: / Line 48: @@
 == rosbag ==
-[http://wiki.ros.org/rosbag|rosbag] is an extremely useful tool to record on file the messages published on ROS topics. You can also use rosbag to "play back" at a later time such messages: for instance, to inspect their content with rviz.
+[http://wiki.ros.org/rosbag rosbag] is an extremely useful tool to record on file the messages published on ROS topics. You can also use rosbag to "play back" at a later time such messages: for instance, to inspect their content with rviz.
 === "Stale" transforms? ===
@@ Line 70: / Line 70: @@
 == tf ==
-From the [http://www.ros.org/wiki/tf the ROS wiki]: "''tf is a package that lets the user keep track of multiple coordinate frames over time. tf maintains the relationship between coordinate frames in a tree structure buffered in time, and lets the user transform points, vectors, etc between any two coordinate frames at any desired point in time''". tf is a key element of ROS and, if you work on mobile robotics, there's not much that you can do with ROS before you discover that you need tf.
+From the [http://www.ros.org/wiki/tf the ROS wiki]: "''tf is a package that lets the user keep track of multiple coordinate frames over time. tf maintains the relationship between coordinate frames in a tree structure buffered in time, and lets the user transform points, vectors, etc between any two coordinate frames at any desired point in time''". [http://wiki.ros.org/tf tf] is a key element of ROS and, if you work on mobile robotics, there's not much that you can do with ROS before you discover that you need tf.
 Basically, every time you have a non-rigid coupling in your robot (including the non-fixed coupling between robot and floor!) it's a good idea to set up a new coordinate frame (i.e., a set of Cartesian xyz axes) on the movable element. Therefore, you will need to define and use the transforms that -given the coordinates in space of a point when measured in one of the frames you defined- produce the coordinates of the same point when measured in another frame. tf lets you define, manage and use such coordinate frames and transforms.
@@ Line 122: / Line 122: @@
 == rviz ==
-rviz is an extremely handy visualizer for data transmitted on ROS topics. It lets the user quickly set up visualizations for most types of ROS messages, including tf transforms, laser data, point clouds, maps, and so on.
+[http://wiki.ros.org/rviz rviz] is an extremely handy visualizer for data transmitted on ROS topics. It lets the user quickly set up visualizations for most types of ROS messages, including tf transforms, laser data, point clouds, maps, and so on.
 To open rviz you need '''roscore''' running in background (execute <code> roscore </code> in a different shell). Then run the following command:

← Older revision		Revision as of 09:48, 9 November 2016
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	== rosbag ==		== rosbag ==
		+	[http://wiki.ros.org/rosbag\|rosbag] is an extremely useful tool to record on file the messages published on ROS topics. You can also use rosbag to "play back" at a later time such messages: for instance, to inspect their content with rviz.

	=== "Stale" transforms? ===		=== "Stale" transforms? ===

← Older revision		Revision as of 09:43, 9 November 2016
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−	This page provides additional information about systems that are an integral part of ROS or that are frequently needed when running or developing a ROS system. Such systems include pieces of the ROS infrastructure (e.g., the parameter server), key ROS packages (e.g., tf) and ~~data inspection/debugging~~ tools (e.g., rviz).	+	This page provides additional information about systems that are an integral part of ROS or that are frequently needed when running or developing a ROS system. Such systems include pieces of the ROS infrastructure (e.g., the parameter server), key ROS packages (e.g., tf) and useful ROS tools (e.g., rosbag, rviz).

	General-purpose information about ROS and its basic elements is available in the ROS HOWTO page.		General-purpose information about ROS and its basic elements is available in the ROS HOWTO page.