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1、Gazebo機器人仿真學(xué)習(xí)探索筆 記（六）工具和實用程序
Gazebo檄器人仿真擘曾探索肇IB （六）
工具和實用程序
Gazebo附帶了許多工具和實用程序。這些教程
說明了這些可用的工具，以及如何使用它們。
主要有:
1記錄和播放
2日志過濾
3應(yīng)用力/扭矩
4 HDF5數(shù)據(jù)集
官網(wǎng)介紹通俗具體，非常容易，請參考附件。
附件-官方教程
Logging and playback
Overview
This tutorial explains how to use the Gazebo logging capabilities to record your simul
2、ation and then reproduce it afterwards, using either the GUI or the command line.
Gazebo log files
Gazebo log files are compressed Jog files which contain an initial full description of the whole
world, followed by a series of nworld states0.
The initial description contains complete information
3、 about everything in the world, from the scene to the entities present
After that, every time something changes in simulation, a new world state is recorded. World states are much simpler, as they only contain information about what changed, such as:
Simulation statistics such as the current simul
4、ation time and the number of physics iterations.
Current state of each model in the scene, as well as the state of each link and joint in the model. This includes information such as instantaneous pose, velocity, acceleration and forces.
Current pose of each light in the world.
Tip: You can find
5、the whole spec for the world state here.
In this tutorial we will record a few log files and then take a peek inside them at the end.
Record a log
Logging from the GUI
Start your simulation. Here, as an example, we have a simple world with a double pendulum.
Click on the logging icon on the top
6、 right, or hit Ctrl+D to bring up the Data Logger.
You can choose the directory where your log file will be saved by clicking the Browse button. By
default, log files Go to the -/.gazebo/log directory. In this example, we will save it in the -/logs/double_pendulum/ directory.
Click on the red
7、 button to start recording. You should see the number of bytes in your log file increasing on the right.
Note: For efficiency, only models and lights which move over time are logged. If your scene is static, the number of bytes in your log file will not increase. This also means that the number of
8、samples in your log file may be different from the number of iterations in simulation.
Click on the red button again to stop logging.
Expand Recordings to see the path to the state.log file which was generated. It will be inside a time-stamped directory.
Logging from the command line
From th
9、e command line, it is possible to log the whole simulation from the moment Gazebo starts running until it stops, or to trigger logging from an arbitary time.
Logging the whole simulation
As an example, you can record the random_velocity.world as follows:
gazebo -r -record_path -/logs/random_veloc
10、ity worlds/random_velocity. world
You can see a list of all of the available logging options by running gazebo -help.
-p [—play] arg: Play a log file.
-r [ -record ]: Record a log from the moment
Gazebo is opened until it is closed.
-record_encoding arg: Compression encoding format for log data
11、. The options are zlib (default), bz2 and txt.
The log file will only be terminated when Gazebo is closed. You can check the file was created by looking into the path given:
$ Is -/logs/random_velocity/
state.log
Logging part of the simulation
Gazebo also provides the gz log tool, which can be
12、used to trigger logging at any moment. While Gazebo is running, open another terminal and run the following to start recording:
gz log -d 1
And to stop:
gz log -d 0
Check out gz log -help for other options.
Play back a log file
Once you have a log file, you can replay it visually or introspect
13、 it in several ways.
Visualize in GUI
Currently, it is not possible to open a log file from the GUI, so playback must be started from the command line. Simply start Gazebo using the -p option to specify a log file, such as the one we recorded earlier:
gazebo -u -p
-/logs/double_pendulum/2016-01-
14、25T15\:09\:49. 677400/gzserver/state.log
Tip: The -u option starts the log paused.
Gazebo will open in playback mode. You can play, pause, rewind and step through the playback.
Use Play / Pause to stop the playback.
Use Rewind / Forward to skip to the beginning / end of the file.
Use Step back
15、/ Step forward to skip samples. The number of samples skipped each time you press a step button can be changed in the box below. Samples might be any number of iterations and seconds apart.
Drag the current time marker and drop it to skip through the log.
Input a current time on the right to skip
16、to that sample.
Command line tools
As mentioned above, the gz log tool provides several options for introspecting your log file. Check out this tutorial for log filtering, for example.
Here, lets quickly go over how you would take a look at the recorded states.
Well use -s to step through a reco
17、rded file, like this:
gz log -s -f
-/logs/double_pendulum/2016-01-25T15\:09\:49. 677400/gzserver/state.log
Youll see the full initial SDF representation of the world, something like this:
(...)
19、e1 >
(...)
(...)
]]>
?一 Press space to continue, Tq* to quit ■一
As you press space, you will step through the subsequent states. Youll note that the states are more compact and only contain information about w
20、hat has changed in the world. Heres an example of a state:
43 380000000
43 478499228
1453763389 677873530
43380
21、del
name= double_pendulum_with_base > 1.
140 -1.074 -0.000 0.000 -0.000 0.000
1.000 1.000 1.0001.13998 -1.07367 -0.00000 0.00000 0.00000 -0.00042
-0.0000 0.0000 -0.0005 0.0004
0.0030 0.0001
22、ink,xpose>1.38969 -1.79815 1.41059 -2.45351 0.00000 -0.00042
0.0042 -0.2557 0.2659 1.9694
0.0048 0.0001 1.13999 -1.07367
2.10000 2.33144 -0.00000 -0.00042
0.0063 -0.0008 -0.0005 -0.3739 0.0032 0.0001
23、nk>0.000 0.000 0.000
0.000 -0.000 0.000 1.000 1.000
1.0000.00000 0.00000 0.00000 0.00000 -0.00000 0.00000 0.0000 0.0000 0.0000 0.0000 -0.0000 0.0000
]]>
24、unk> ■" Press space to continue, fqf to quit ■一
Note that there *s no information for the sun or
the ground_plane, since they are not moving.
Log filtering
Introduction
State logs are recordings of world state information from Gazebo. State includes pose, velocity, acceleration, and forces appl
25、ied to all links of all models. Gazebo will only record state information for models that change over time. A state log file contains a header, the initial world description, and a time series of state.
Gazebo Log Command line tool
Gazebo ships with a logging utility that is accessed via the gz lo
26、g command.
View the help information using:
gz help log or
gz log -h
Example Usage
Tip: Check out the tutorial on logging and playback for an overview of ways to record a log-
Step 1: Create a state log file
Start by removing old log files
rm -rf -/.gazebo/log/*
We will use the PR2 world to
27、 create a state log file.
Start by running the Gazebo server with the -r command line option
gzserver -r worlds/pr2.world
After a few seconds, stop the server using ctrl-c.
A new time stamped directory should exist in -Agazebo/log with one subdirectory and a state.log file. Here is an example
?
28、/?gazebo/log/2013?07?25T07\:29\:05.122275/gzse rver/state.log
You can verify this log file by replaying it in Gazebo.
gazebo -p -Agazebo/log/^/gzserver/state.log
Step 2: Filter a state log file
The gz log command line tool provides mechanisms for stepping through a log file and echoing the conte
29、nts of a log file to screen. The echo to screen feature can be combined with a filter to produce a log file that contains specific information such as just the pose of models and links.
Try echoing the recorded state log file to screen.
gz log -e -f -/.gazebo/log/*/gzserver/state.log You should se
30、e a lot of information scroll by.
Now lefs remove all velocity, acceleration, and force information from the log file. This will
leave just pose information.
gz log -e -f -Agazebo/log/*/gzserver/state.log
-filter *.pose/*.pose
The -filter option is a flexible command line argument to extract in
31、formation from a log file.
It is also possible to filter based on simulation time using a Hz filter. For example, we can output state information at 30 Hz using:
gz log -e -f -Agazebo/log/^/gzserver/state.log -z 30
These filters can be combined and piped to a file for playback. This may take some
32、 time depending on the size of the state.log.
gz log -e -f -Agazebo/log/*/gzserver/state.log -z 30 -filter *.pose/*.pose > /tmp/filtered_state.log This log file can then be replayed in Gazebo gazebo -p /tmp/filtered_state.log
Applying Force/Torque
Introduction
This tutorial will explain how to a
33、pply force and/or torque to models during simulation using the graphical user interface.
Applying force and torque examples
Lets go through an example of applying force and torque to simple models. Open Gazebo and from the insert tab, insert a Simple Arm into the scene. Then, from the top toolbar,
34、 insert a box. Make sure the simulation is not paused.
Apply force to a link
We want to apply force to a specific link in the
Simple Arm model. On the World tree, right-click arm_wrist_lift and choose Apply Force/Torque. A dialog will pop up and youTll see a straight arrow and a curved arrow
35、attach to the arm.
On the dialog, write 100 N on the Y field under Force and press Enter, the arm will start rotating slightly. The force was applied in the links Y direction for a single time-step, which is in the order of milliseconds, thus the need for such a large force.
Apply torque to a
36、link
On Apply to link, select arm_elbow_pan9 the arrows will move to this link. Under torque, write 100 Nm on the Z field and press Apply
Torque a few times to see the arm rotate slightly.
Apply force with an offset
Now lets apply force to the box. Right-click the box in the scene and choose
37、 Apply Force/Torque. A new dialog will pop up.
Under Force, type 1000 N on the X field. Then under Application point, press the up arrow in the Y field until it reaches 1 m, youll see the arrow oving as you do it. Press Enter a few times to and the box will rotate. Hold Enter to repeatedly apply th
38、e force and make the box spin fasten
The interface explained
Note: If you apply force and/or torque while the simulation is paused, they will accumulate and be applied all at once when the simulation is unpaused.
Force
X, Y, Z: Each field specifies how much force will be applied on that dire
39、ction. The frame is fixed to the link.
Mag: The total magnitude of the force which will be applied, which is the Euclidean norm of the 3 forces above. Changing the magnitude changes the XYZ fields proportionally, maintaining the force direction.
Clear: Pressing this button will zero the X, Y, Z an
40、d Mag 加Ids.
Application point: By default, force is applied to the links center of mass. Here you can edit the X, Y and Z fields to give the force an offset with respect to the links origin expressed in the links frame. Select Center of mass again to Oil the XYZ fields with its coordinates.
Tip: R
41、ight-click the model and choose View -> Center of mass to see its position. You might want to also make the model transparent for that.
Apply Force: Click this to apply only force for one time step. Keep in mind that time steps are in the order of milliseconds, so relatively large forces are needed
42、 in order to apply a signifleant impulse.
Torque
X, Y, Z: Each field specifies how much torque
will be applied about that axis. The frame is fixed to the link.
Mag: The total magnitude of the torque which will be applied, which is the Euclidean norm of the 3 torques above. Changing the magnitude
43、 changes the XYZ fields proportionally, maintaining the torque direction.
Clear: Pressing this button will zero the X, Y, Z and Mag 加Ids.
Apply Torque: Click this to apply only torque for one time step. Keep in mind that time steps are in the order of milliseconds, so relatively large torques are
44、needed in order to apply a significant angular impulse.
Note: Torque is always applied about the center of mass.
Apply All
Force and torque are applied at the same time,
i.e. apply a wrench. Hold enter or click it repeatedly to apply multiple times.
Rotation tool
The arrows directions will alw
45、ays match the directions specified in the dialog. From the dialog, the direction can be changed by editing the numbers on the XYZ fields. From the scene, the direction can be changed by dragging the pink circles around the arrows.
Tip: The pink circles are attached to the highlighted arrow. To rota
46、te the other arrow, first click it to attach the circles to it and then drag them normally.
Instrument HDF5 Datasets
Introduction
Instrument tools are provided to dump physical data into HDF5 format. The datasets, together with the Benchmark Problems for Multibody Dynamis (BPMD) framework are use
47、d to
compare different methods in solving multibody systems with bilateral joints and unilateral frictional contacts in an unbiased way. These datasets will help researchers to concentrate on analysis of existing methods and construction of more accurate solvers, without worrying about implementati
48、on of the whole physics engine.
Example Usage
Install hdf5
sudo apt-get install libhdf5-dev
Build Gazebo
This HDF5 instrument tool requires building Gazebo from source, with the cmake parameter HDF5_INSTRUMENT [default False] as True. Learn how to build Gazebo from source
cd -/gazebo
mkdir bu
49、ild
cd build
cmake -DHDF5_INSTRUMENT=True../
make -j4
sudo make install
Collect Datasets
Use only gzserver
./test/integration/INTEGRATION_physics_inert ia_ratio
Use the world file
gazebo -/gazebo/worlds/friction_demo.world
Then a file named ode_frames.hdf5 will be generated at the director
50、y exactly where the above command is run.
View the HDF5 file
hdfvivew is used to open the hdf5 files. You can install it via the terminal:
sudo apt-get install hdfview
Then open the stored file with: hdfview ode_frames.hdf5
A hierarchical file shows up:
Nofe: The instrument tool will save hier
51、archical
dafa for each time sfep? so it will be slow to write -he data info the ode—frames.hdf5 m9 Be pa-ienL especially for complex simulafion scenarios such as AUas robots or many body simulation.
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Gazebo機器人仿真學(xué)習(xí)探索筆記(六)工具和實用程序
