# ubuntu16 安装gym-gazebo ## 目录 本节会安装以下内容 * Kinetic * ubuntu16 * gazebo8 * gym * python3.5 * opencv3 * 安装 gazebo\_ros\_pkgs * gym-gazebo * gym-gazebo 测试 本节笔记主要记录ubuntu16 下安装gym-gazebo，包括其依赖的软件包安装。 我的代码仓库: 建议直接clone 我的软件仓库安装(直接适应kinetic版本安装不会出现警告和编译出错终止，当然可能会应为你的ros功能包缺失出错,这时只需要手动安装缺失的ros功能包，删除catkin\_ws，再重复上次的安装过程即可) ```bash cd ~ git clone -b master https://github.com/porterpan/gym-gazebo ``` > 实在官方的仓库中修改了: \~/gym-gazebo/gym\_gazebo/envs/installation/gazebo.repos 文件内容.使整个安装适应ROS kinetic 环境。当然过程中如果缺ros功能包，需要自己额外安装功能包的。 > > 缺失ros功能包会在编译时出现make error 红色的， 解决办法见[ROS 中功能包的安装与查询](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#ros-中功能包的安装与查询) 部分的方法安装好，然后remove -rf 安装路径中的catkin\_ws 文件夹，然后重新上一步操作安装即可。 * [ ] [目录](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#目录) * [ ] [第一部分安装gym-gazebo](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#第一部分安装gym-gazebo) * [下载安装文件](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#下载安装文件) * [安装依赖环境](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#安装依赖环境) * [Basic requirements:](/deep-learning-series/di-si-zhang-ros-ji-qi-ren/ubuntu16-an-zhuang-gymgazebo.md#basic-requirements) * [Install Sophus](/deep-learning-series/di-si-zhang-ros-ji-qi-ren/ubuntu16-an-zhuang-gymgazebo.md#install-sophushttpsgithubcomstoniersophustreerelease091-kinetic) * [安装gym-gazebo](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#安装gym-gazebo) * [Dependencies and libraries](/deep-learning-series/di-si-zhang-ros-ji-qi-ren/ubuntu16-an-zhuang-gymgazebo.md#dependencies-and-libraries) * [install Theano](/deep-learning-series/di-si-zhang-ros-ji-qi-ren/ubuntu16-an-zhuang-gymgazebo.md#install-theano) * [install Keras](/deep-learning-series/di-si-zhang-ros-ji-qi-ren/ubuntu16-an-zhuang-gymgazebo.md#install-keras) * [Try it out (turtlebot simple env)](/deep-learning-series/di-si-zhang-ros-ji-qi-ren/ubuntu16-an-zhuang-gymgazebo.md#try-it-out-turtlebot-simple-env) * [Agent dependencies:](/deep-learning-series/di-si-zhang-ros-ji-qi-ren/ubuntu16-an-zhuang-gymgazebo.md#agent-dependencies) * [Run the environment with a sample agent:](/deep-learning-series/di-si-zhang-ros-ji-qi-ren/ubuntu16-an-zhuang-gymgazebo.md#run-the-environment-with-a-sample-agent) * [ ] [第二部分：附录](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#第二部分附录) * [ROS 中功能包的安装与查询](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#ros-中功能包的安装与查询) * [1.查询当前安装完成的所有包文件](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#1查询当前安装完成的所有包文件) * [2.查询ros的所有功能包](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#2查询ros的所有功能包) * [安装错误解决](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#安装错误解决) * [错误1：](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#错误1) * [问题2](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#问题2) * [问题3：](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#问题3) * [ ] [gazebo.repos　内容修改](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#gazeborepos　内容修改) * [ ] [安装结束效果](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#安装结束效果) * [问题4：](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#问题4) * [问题5：](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#问题5) * [ ] [gym-gazebo 测试](https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/pages/-LeAUUkh1ddy0EDZMXjc#gym-gazebo-测试) * [x] Edit By Porter, 积水成渊,蛟龙生焉。 ## 第一部分安装gym-gazebo ### 下载安装文件 ```bash cd ~ #进入home目录 git clone -b master https://github.com/porterpan/gym-gazebo ``` ### 安装依赖环境 #### Basic requirements: * [ROS Kinetic](http://wiki.ros.org/kinetic/Installation/Ubuntu#Installation-1) (/rosversion: 1.12.7) (安装选择这个sudo apt-get install ros-kinetic-desktop, 不要全装不然后面装gazebo8会相对麻烦点) > 进入ROS官网的安装界面： > > 选择需要的版本 Kinetic 和系统平台，我们用的是 ubuntu 16.04 按照指导进行安装，这里注意要选择安装 ros-kinetic-desktop 版本，不要选 ros-kinetic-desktop-full，前者不包含 Gazebo ，后者包含了 Gazebo 7。后边安装 Gazebo 8 的时候还需要卸载掉，比较麻烦。 按照完 ROS 测试一下，在命令行中输入如下命令，看能否正常启动 ros master ： > > 作者：isl\_qdu 链接： 来源：简书 简书著作权归作者所有，任何形式的转载都请联系作者获得授权并注明出处。 * [Gazebo 8.1.1](http://gazebosim.org/tutorials?cat=install\&tut=install_ubuntu\&ver=8.0) , 进入选择手动安装，不要选择Default installation: one-liner安装方式，否则会给你安装默认最新版本的gazebo. * Python 3.5.2 (# I have yet to find out why though, because all the standard ROS stuff is in Python 2) * [OpenCV3, installed from sources for Python 3， pip3](https://pypi.org/project/opencv-python/3.4.3.18/#history) 或者手动安装(git clone ) * 安装 gazebo\_ros\_pkgs > 前边安装的 ROS 与 Gazebo 是完全独立的两部分，要使他们之间互相通讯，还需要安装 gazebo\_ros\_pkgs 包。 > > 进入官网安装界面： > > 按照指导安装即可。我一般选择用 A: Install Pre-Built Debians 方式安装。需要注意的是，如果用如下命令安装报错： > > ```bash > sudo apt-get install ros-kinetic-gazebo-ros-pkgs ros-kinetic-gazebo-ros-control > ``` > > 则需要指明 Gazebo 版本，将命令改为： > > ```bash > sudo apt-get install ros-kinetic-gazebo8-ros-pkgs ros-kinetic-gazebo8-ros-control > ``` > > 就可以解决问题。 测试。安装结束，用如下命令测试： ```bash roscore # 启动 ros master rosrun gazebo_ros gazebo # 用 rosrun 方式启动 Gazebo ``` > 作者：isl\_qdu 链接： 来源：简书 简书著作权归作者所有，任何形式的转载都请联系作者获得授权并注明出处。 * [OpenAI gym安装](http://gym.openai.com/docs/) #### [Install Sophus](https://github.com/stonier/sophus/tree/release/0.9.1-kinetic) ```bash cd ~ git clone https://github.com/stonier/sophus -b release/0.9.1-kinetic cd sophus mkdir build cd build cmake .. make sudo make install echo "## Sophus installed ##\n" ``` ### 安装gym-gazebo ```bash cd ~ Gazebo gym git clone -b master https://github.com/erlerobot/gym-gazebo cd gym-gazebo sudo pip2 install -e . ``` #### Dependencies and libraries ```bash sudo pip3 install h5py sudo apt-get install python3-skimage ``` #### install Theano ```bash cd ~/ git clone git://github.com/Theano/Theano.git cd Theano/ sudo python3 setup.py develop ``` #### install Keras ```bash sudo pip3 install keras ``` ### Try it out (turtlebot simple env) * Issues: > spacenav\_node not compiling. CATKIN\_IGNOREd. wiimote not compiling. CATKIN\_IGNOREd. kobuki\_qtestsuite not compiling. CATKIN\_IGNOREd. #### Agent dependencies: ```bash # make sure to switch to bash, because the installation script # hasn't been converted to ZSH yet # and if you run it from ZSH the environmental variables # that are set during the script's execution aren't preserved cd gym_gazebo/envs/installation ./setup_kinetic.bash ./turtlebot_setup.bash ``` ### Run the environment with a sample agent: ```bash # only execute this while still in the same bash as last step cd ../../../examples/scripts_turtlebot/ python circuit2_turtlebot_lidar_qlearn.py ``` The result should look like this (after a few seconds): ``` ... (messages about ROS and Gazebo starting up, until finally:) ... [ INFO] [1508869124.880487247, 81.480000000]: GazeboRosKobuki plugin ready to go! [mobile_base] EP: 1 - [alpha: 0.2 - gamma: 0.8 - epsilon: 0.9] - Reward: -87 Time: 0:00:05 EP: 2 - [alpha: 0.2 - gamma: 0.8 - epsilon: 0.9] - Reward: -155 Time: 0:00:05 EP: 3 - [alpha: 0.2 - gamma: 0.8 - epsilon: 0.9] - Reward: -165 Time: 0:00:05 EP: 4 - [alpha: 0.2 - gamma: 0.8 - epsilon: 0.89] - Reward: -156 Time: 0:00:06 EP: 5 - [alpha: 0.2 - gamma: 0.8 - epsilon: 0.89] - Reward: -162 Time: 0:00:06 EP: 6 - [alpha: 0.2 - gamma: 0.8 - epsilon: 0.89] - Reward: -161 Time: 0:00:07 EP: 7 - [alpha: 0.2 - gamma: 0.8 - epsilon: 0.89] - Reward: -167 Time: 0:00:07 EP: 8 - [alpha: 0.2 - gamma: 0.8 - epsilon: 0.89] - Reward: -166 Time: 0:00:08 EP: 9 - [alpha: 0.2 - gamma: 0.8 - epsilon: 0.89] - Reward: -154 Time: 0:00:08 EP: 10 - [alpha: 0.2 - gamma: 0.8 - epsilon: 0.89] - Reward: -157 Time: 0:00:09 ``` ## 第二部分：附录 ### ROS 中功能包的安装与查询 #### 1.查询当前安装完成的所有包文件 ```bash rospack list ``` * 可以看到所有的ROS功能包都在/opt/ros/kinetic/share目录下，所以也可以使用如下命令查询 ```bash cd /opt/ros/kinetic/share/ or roscd turtlesim/ cd .. ``` **2.查询ros的所有功能包** ```bash apt-cache search ros-kinetic ``` * 或者说在不知道要安装功能包的确切名字的情况下找到目标包 ```bash apt-cache search ros-kinetic | grep rqt- ``` > 通过管道线 与grep命令， 输出与关键字rqt-相关的行 * 再或者下述安装命令与Tab键结合 ```bash sudo apt-get install ros-kinetic-rqt- ``` > 系统输出相应提示。 前述所有内容中，rospack list 与sudo apt-get install ros-kinetic-rqt- +Tab键使用最方便。 ### 安装错误解决 #### 错误1： * 错误1：错误提示： > 在moveit编译时找不到manipulation\_msgsConfig.cmake manipulation\_msgs-config.cmake文件 > > \`\`\`bash Could not find the required component 'manipulation\_msgs'. The following CMake error indicates that you either need to install the package with the same name or change your environment so that it can be found. CMake Error at /opt/ros/kinetic/share/catkin/cmake/catkinConfig.cmake:83 (find\_package): Could not find a package configuration file provided by "manipulation\_msgs" with any of the following names: manipulation\_msgsConfig.cmake manipulation\_msgs-config.cmake 作者：pd很不专业 来源：CSDN 原文： 版权声明：本文为博主原创文章，转载请附上博文链接！ ```` ![manipulation_msgsconfig.cmake](./image4/manipulation_msgsconfig.cmake) - 错误1：解决： 搜索这个功能包 ![manipulation_msgsconfig.search](./image4/manipulation_msgsconfig.search.png) 能找到这个ros-kinetic-manipulation-msgs 包 ```bash sudo apt-get install ros-kinetic-manipulation-msgs ```` > 对ros安装对应的manipulation\_msgsConfig包, 完成安装后重新去编译一下你的moveit包就行了。 ![manipulation\_msgsconfig.installed](/files/-LeAUVKWKyW-MFPpFnuM) #### 问题2 * 错误二：错误提示： ```bash " CMake Error at /opt/ros/kinetic/share/catkin/cmake/catkinConfig.cmake:83 (find_package): Could not find a package configuration file provided by "tf2_geometry_msgs" with any of the following names: tf2_geometry_msgsConfig.cmake tf2_geometry_msgs-config.cmake Add the installation prefix of "tf2_geometry_msgs" to CMAKE_PREFIX_PATH or set "tf2_geometry_msgs_DIR" to a directory containing one of the above files. If "tf2_geometry_msgs" provides a separate development package or SDK, be sure it has been installed." ``` * 错误二：解决： 先搜索这个需要安装的ros功能包 ```bash apt-cache search ros-kinetic | grep tf2_geometry_msgs ``` 发现存在这个包 ```bash porter@porter-Aspire:~/gym-gazebo/gym_gazebo/envs/installation$ apt-cache search ros-kinetic | grep tf2_geometry_msgs ros-kinetic-tf2-geometry-msgs - tf2_geometry_msgs ``` 执行这个功能包的安装 ```bash porter@porter-Aspire:~/gym-gazebo/gym_gazebo/envs/installation$ sudo apt-get install ros-kinetic-tf2-geometry-msgs [sudo] porter 的密码： 正在读取软件包列表... 完成 正在分析软件包的依赖关系树 正在读取状态信息... 完成 下列【新】软件包将被安装： ros-kinetic-tf2-geometry-msgs 升级了 0 个软件包，新安装了 1 个软件包，要卸载 0 个软件包，有 0 个软件包未被升级。 需要下载 0 B/13.2 kB 的归档。 解压缩后会消耗 86.0 kB 的额外空间。 正在选中未选择的软件包 ros-kinetic-tf2-geometry-msgs。 (正在读取数据库 ... 系统当前共安装有 415109 个文件和目录。) 正准备解包 .../ros-kinetic-tf2-geometry-msgs_0.5.20-0xenial-20190320-171251-0800_amd64.deb ... 正在解包 ros-kinetic-tf2-geometry-msgs (0.5.20-0xenial-20190320-171251-0800) ... 正在设置 ros-kinetic-tf2-geometry-msgs (0.5.20-0xenial-20190320-171251-0800) ... porter@porter-Aspire:~/gym-gazebo/gym_gazebo/envs/installation$ ``` ![tf2\_geometry\_msg\_resolved.png](/files/-LeAUVK_LbUYPqDEsi38) #### 问题3： * 问题3：错误提示 CMake Error at /opt/ros/kinetic/share/catkin/cmake/catkin\_workspace.cmake:95 (message): ```bash WARNING: Metapackage "ecl_tools" must buildtool_depend on catkin. WARNING: Metapackage "ecl_tools" should not have other dependencies besides a buildtool_depend on catkin and run_depends. WARNING: Metapackage "ecl_lite" must buildtool_depend on catkin. WARNING: Metapackage "ecl_lite" should not have other dependencies besides a buildtool_depend on catkin and run_depends. Packages "mav_msgs" not found in the workspace ``` * 问题3：解决 出现这个错误的原因是ecl升级，或这和你当前安装的ros版本不对应。造成了cmake版本比配。出错，方法是 打开gazebo.repos,修改如下部分： ```bash ecl_lite: type: git url: https://github.com/stonier/ecl_lite version: release/0.61-indigo-kinetic ecl_navigation: type: git url: https://github.com/stonier/ecl_navigation version: devel ecl_tools: type: git url: https://github.com/stonier/ecl_tools version: release/0.61-indigo-kinetic ``` (将ecl\_core、 ecl\_lite 和ecl\_tools 的版本号（version）改成： release/0.61-indigo-kinetic） **不过最终解决还是建议你如果也是安装ros kenitic 直接复制我后面附录的gazebo.repos内容替换掉之前的** 路径： vim \~/gym-gazebo/gym\_gazebo/envs/installation/gazebo.repos ## gazebo.repos　内容修改 gazebo.repos 修改后的文件内容，使适应kinetic环境，进行安装。 ``` repositories: ar_track_alvar: type: git url: https://github.com/ros-perception/ar_track_alvar version: kinetic-devel mav_comm: type: git url: https://github.com/ethz-asl/mav_comm.git version: master catkin_simple: type: git url: https://github.com/catkin/catkin_simple.git version: master control_toolbox: type: git url: https://github.com/ros-controls/control_toolbox.git version: kinetic-devel ecl_core: type: git url: https://github.com/stonier/ecl_core version: release/0.61-indigo-kinetic ecl_lite: type: git url: https://github.com/stonier/ecl_lite version: release/0.61-indigo-kinetic ecl_navigation: type: git url: https://github.com/stonier/ecl_navigation version: release/0.60-indigo-kinetic ecl_tools: type: git url: https://github.com/stonier/ecl_tools version: release/0.61-indigo-kinetic driver_base: type: git url: https://github.com/ros-drivers/driver_common.git version: indigo-devel gazebo_ros_pkgs: type: git url: https://github.com/ros-simulation/gazebo_ros_pkgs version: kinetic-devel hector_gazebo: type: git url: https://github.com/tu-darmstadt-ros-pkg/hector_gazebo/ version: kinetic-devel image_common: type: git url: https://github.com/ros-perception/image_common.git version: hydro-devel joystick_drivers: type: git url: https://github.com/ros-drivers/joystick_drivers.git version: master kobuki: type: git url: https://github.com/yujinrobot/kobuki version: kinetic kobuki_core: type: git url: https://github.com/yujinrobot/kobuki_core version: kinetic kobuki_desktop: type: git url: https://github.com/yujinrobot/kobuki_desktop version: kinetic kobuki_msgs: type: git url: https://github.com/yujinrobot/kobuki_msgs version: kinetic navigation: type: git url: https://github.com/ros-planning/navigation version: kinetic-devel pcl_ros: type: git url: https://github.com/ros-perception/perception_pcl.git version: kinetic-devel realtime_tools: type: git url: https://github.com/ros-controls/realtime_tools version: kinetic-devel ros_control: type: git url: https://github.com/ros-controls/ros_control version: kinetic-devel roslint: type: git url: https://github.com/ros/roslint version: master turtlebot: type: git url: https://github.com/turtlebot/turtlebot version: kinetic turtlebot_create: type: git url: https://github.com/turtlebot/turtlebot_create version: master turtlebot_simulator: type: git url: https://github.com/turtlebot/turtlebot_simulator version: indigo xacro: type: git url: https://github.com/ros/xacro version: kinetic-devel yocs_msgs: type: git url: https://github.com/yujinrobot/yocs_msgs version: release/0.6-kinetic yujin_ocs: type: git url: https://github.com/yujinrobot/yujin_ocs version: kinetic ``` ## 安装结束效果 ```bash vim ~/.bashrc # 最后几行的环境应该是这样的 source /home/porter/gym-gazebo/gym_gazebo/envs/installation/catkin_ws/devel/setup.bash export GAZEBO_MODEL_PATH=/home/porter/gym-gazebo/gym_gazebo/envs/installation/../assets/models export GYM_GAZEBO_WORLD_MAZE=/home/porter/gym-gazebo/gym_gazebo/envs/installation/../assets/worlds/maze.world export GYM_GAZEBO_WORLD_CIRCUIT=/home/porter/gym-gazebo/gym_gazebo/envs/installation/../assets/worlds/circuit.world export GYM_GAZEBO_WORLD_CIRCUIT2=/home/porter/gym-gazebo/gym_gazebo/envs/installation/../assets/worlds/circuit2.world export GYM_GAZEBO_WORLD_CIRCUIT2C=/home/porter/gym-gazebo/gym_gazebo/envs/installation/../assets/worlds/circuit2c.world export GYM_GAZEBO_WORLD_ROUND=/home/porter/gym-gazebo/gym_gazebo/envs/installation/../assets/worlds/round.world ``` 打开终端执行的效果如下图 ![gym\_gazebo\_success](/files/-LeAagutFX84V4fabY_s) #### 问题4： * 问题4：错误提示 Pycharm 里面无法正常运行Gym\_gazebo代码. [ubuntu下PyCharm导入ros库](https://blog.csdn.net/wuguangbin1230/article/details/79300578) porter\@porter-Aspire:\~$ gedit /usr/share/applications/Pycharm.desktop ```bash [Desktop Entry] Type=Application Name=Pycharm GenericName=Pycharm3 Comment=Pycharm3:The Python IDE Exec=sh /home/porter/pycharm-2018.3.5/bin/pycharm.sh Icon=/home/porter/pycharm-2018.3.5/bin/pycharm.png Terminal=pycharm Categories=Pycharm; ``` * 问题4：错误提示 ```bash [Desktop Entry] Version=1.0 Type=Application Name=Pycharm GenericName=Pycharm3 Icon=/home/porter/pycharm-2018.3.5/bin/pycharm.png Exec=bash -i -c "/home/porter/pycharm-2018.3.5/bin/pycharm.sh" %f Comment=Pycharm3:The Python IDE Categories=Development;IDE; Terminal=false ``` #### 问题5： [在终端中正常运行，在pycharm中运行出错](https://blog.csdn.net/Dawn__Z/article/details/82454717) * 问题5：错误提示 ```bash entry = _cache.get(encoding, _unknown) AttributeError: ‘NoneType’ object has no attribute ‘get’ ``` 运行pycharm报错，内容如下： ![no attribute ‘get’](/files/-Lf2VneNogPp74gk9g3E) * 问题5：解决方式： settings -> tools ->Python Scientific ->Show plots in toolwindow(取消勾选) ![plots in toolwindow](/files/-Lf2VnePbHJ58wSLkRxA) ## gym-gazebo 测试 参见我的另一篇文章[gym-gazebo安装后的测试](/deep-learning-series/di-si-zhang-ros-ji-qi-ren/gymgazebo-an-zhuang-hou-de-ce-shi.md) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://porter.gitbook.io/deep-learning-series/di-si-zhang-ros-ji-qi-ren/ubuntu16-an-zhuang-gymgazebo.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.