ROS 2 用户指南
ROS 2-PX4 架构在ROS 2和PX4之间进行了深度整合。 允许 ROS 2 订阅或发布节点直接使用 PX4 uORB 话题。
本指南介绍了系统架构和应用程序流程，并解释了如何与PX4一起安装和使用ROS2。
From PX4 v1.14, ROS 2 uses uXRCE-DDS middleware, replacing the FastRTPS middleware that was used in version 1.13 (v1.13 does not support uXRCE-DDS).
The migration guide explains what you need to do in order to migrate ROS 2 apps from PX4 v1.13 to PX4 v1.14.
If you're still working on PX4 v1.13, please follow the instructions in the PX4 v1.13 Docs.
概述
由于使用 uXRCE-DDS 通信中间件，因此ROS 2的应用程序流程非常简单。
uXRCE-DDS的中间件由运行在PX4上的客户端(Client)和运行在机载计算机上的代理端(Agent)组成， 通过串口、UDP、TCP或其他链路实现双向数据互联。 代理端(Agent)充当客户端(Client)的代理在DDS全局数据空间中发布和订阅话题。
The PX4 uxrce_dds_client is generated at build time and included in PX4 firmware by default. 它包含“通用”XRCE-DDS客户端(Client)代码和PX4 特定翻译代码以支持用来发布或获取来自uORB的话题 。 为客户端(Client)生成的 uORB 消息的子集在 PX4-Autopilot/src/modules/uxrce_dds_client/dds_topics.yaml 中定义。 生成器使用代码树： PX4-Autopilot/msg 中的 uORB 消息定义来创建 ROS 2 消息代码。
ROS 2 应用程序应该在具有 相同的 消息定义的工作区中构建，即在 PX4 Firmware 中创建 uXRCE-DDS客户端(Client)模块时使用的消息。 你可以通过克隆接口包 PX4/px4_msgs 到你的 ROS 2 工作空间中(仓库中的分支对应于不同版本 PX4 消息)。
请注意，micro XRCE-DDS 代理(Agent) 本身并不依赖客户端代码。 可以通过 源码单独或作为ROS的一部分通过编译生成，也可以通过snap安装。
您通常需要在使用 ROS 2 时同时启动客户端(Client)和代理人(Agent)。 请注意，uXRCE-DDS客户端默认是编译进固件中的，但除模拟器构建外，不会自动启动。
In PX4v1.13 and earlier, ROS 2 was dependent on definitions in px4_ros_com. 该仓库不再需要了，但的确包含了有用的例子。
安装设置
The supported ROS 2 platforms for PX4 development are ROS 2 "Humble" on Ubuntu 22.04, and ROS 2 "Foxy" on Ubuntu 20.04.
ROS 2 "Humble" is recommended because it is the current ROS 2 LTS distribution. ROS 2 "Foxy" reached end-of-life in May 2023, but is still stable and works with PX4.
PX4 is not as well tested on Ubuntu 22.04 as it is on Ubuntu 20.04 (at time of writing), and Ubuntu 20.04 is needed if you want to use Gazebo Classic.
To setup ROS 2 for use with PX4:
框架的其他依赖关系将自动安装，如 Fast DDS。
安装PX4
您需要安装 PX4 开发工具链才能使用模拟器。
The only dependency ROS 2 has on PX4 is the set of message definitions, which it gets from px4_msgs. 您只需要安装 PX4 当您需要模拟器时(如我们在本指南中所做的那样)， 或者如果您正在创建一个发布自定义uORB话题。
通过以下方式在 Ubuntu 上配置一个 PX4 开发环境：
sh
cd
git clone https://github.com/PX4/PX4-Autopilot.git --recursive
bash ./PX4-Autopilot/Tools/setup/ubuntu.sh
cd PX4-Autopilot/
make px4_sitlNote that the above commands will install the recommended simulator for your version of Ubuntu. If you want to install PX4 but keep your existing simulator installation, run ubuntu.sh above with the --no-sim-tools flag.
For more information and troubleshooting see: Ubuntu Development Environment and Download PX4 source.
安装 ROS 2
安装 ROS 2 及其依赖：
Install ROS 2.
:::
::::
一些Python 依赖关系也必须安装 (使用
pip或apt):shpip install --user -U empy==3.3.4 pyros-genmsg setuptools
安装Micro XRCE-DDS 代理(Agent)& 客户端(Client)
For ROS 2 to communicate with PX4, uXRCE-DDS client must be running on PX4, connected to a micro XRCE-DDS agent running on the companion computer.
设置代理(Agent)
代理(Agent)可以通过 数种方式 安装到任务计算机上。 下面我们将演示如何从源代码构建“独立”代理(Agent)，并连接到在 PX4 模拟器上运行的客户端(Client)。
设置并启动代理：
打开一个终端。
输入以下命令从仓库获取源代码并构建代理(Agent)：
shgit clone https://github.com/eProsima/Micro-XRCE-DDS-Agent.git cd Micro-XRCE-DDS-Agent mkdir build cd build cmake .. make sudo make install sudo ldconfig /usr/local/lib/启动代理并设置以连接运行在模拟器上的 uXRCE-DDS客户端(Client)：
shMicroXRCEAgent udp4 -p 8888
代理正在运行，但在我们启动PX4 (下一步)之前，您不会看到太多。
INFO
You can leave the agent running in this terminal! 请注意，每个连接端口只允许一个代理(Agent)。
启动客户端(Client)
PX4 模拟器自动启动 uXRCE-DDS客户端，连接到本地主机上的 UDP 8888 端口。
启动模拟器(和客户端Client)：
Open a new terminal in the root of the PX4 Autopilot repo that was installed above.
:::
::::
代理(Agent)和客户端(Client)现在将运行并建立连接。
PX4 终端显示 NuttShell/PX4 系统控制台 PX4 启动和运行。 代理(Agent)连接后输出应该包含 INFO 显示创建数据写入的消息：
...
INFO [uxrce_dds_client] synchronized with time offset 1675929429203524us
INFO [uxrce_dds_client] successfully created rt/fmu/out/failsafe_flags data writer, topic id: 83
INFO [uxrce_dds_client] successfully created rt/fmu/out/sensor_combined data writer, topic id: 168
INFO [uxrce_dds_client] successfully created rt/fmu/out/timesync_status data writer, topic id: 188
...Micro XRCE-DDS代理(Agent)终端也应开始显示输出，因为DDS网络中创建了相同的主题：
...
[1675929445.268957] info | ProxyClient.cpp | create_publisher | publisher created | client_key: 0x00000001, publisher_id: 0x0DA(3), participant_id: 0x001(1)
[1675929445.269521] info | ProxyClient.cpp | create_datawriter | datawriter created | client_key: 0x00000001, datawriter_id: 0x0DA(5), publisher_id: 0x0DA(3)
[1675929445.270412] info | ProxyClient.cpp | create_topic | topic created | client_key: 0x00000001, topic_id: 0x0DF(2), participant_id: 0x001(1)
...Build ROS 2 Workspace
本节将展示如何在您的主目录中创建一个 ROS 2 工作空间(将源代码放在别处需要修改相关指令)。
px4_ros_com and px4_msgs 软件包克隆到一个工作区文件夹，然后使用 colcon 工具来构建工作区。 The example is run using ros2 launch.
The example builds the ROS 2 Listener example application, located in px4_ros_com. px4_msgs is needed too so that the example can interpret PX4 ROS 2 topics.
Building the Workspace
To create and build the workspace:
Open a new terminal.
Create and navigate into a new workspace directory using:
shmkdir -p ~/ws_sensor_combined/src/ cd ~/ws_sensor_combined/src/INFO
A naming convention for workspace folders can make it easier to manage workspaces. :::
Clone the example repository and px4_msgs to the
/srcdirectory (themainbranch is cloned by default, which corresponds to the version of PX4 we are running):shgit clone https://github.com/PX4/px4_msgs.git git clone https://github.com/PX4/px4_ros_com.gitSource the ROS 2 development environment into the current terminal and compile the workspace using
colcon:
:::
::::
This builds all the folders under /src using the sourced toolchain.
Running the Example
To run the executables that you just built, you need to source local_setup.bash. This provides access to the "environment hooks" for the current workspace. In other words, it makes the executables that were just built available in the current terminal.
The ROS2 beginner tutorials recommend that you open a new terminal for running your executables.
In a new terminal:
Navigate into the top level of your workspace directory and source the ROS 2 environment (in this case "Humble"):
:::
::::
Source the
local_setup.bash.shsource install/local_setup.bashNow launch the example. Note here that we use
ros2 launch, which is described below.ros2 launch px4_ros_com sensor_combined_listener.launch.py
If this is working you should see data being printed on the terminal/console where you launched the ROS listener:
sh
RECEIVED DATA FROM SENSOR COMBINED
================================
ts: 870938190
gyro_rad[0]: 0.00341645
gyro_rad[1]: 0.00626475
gyro_rad[2]: -0.000515705
gyro_integral_dt: 4739
accelerometer_timestamp_relative: 0
accelerometer_m_s2[0]: -0.273381
accelerometer_m_s2[1]: 0.0949186
accelerometer_m_s2[2]: -9.76044
accelerometer_integral_dt: 4739Controlling a Vehicle
To control applications, ROS 2 applications:
- subscribe to (listen to) telemetry topics published by PX4
- publish to topics that cause PX4 to perform some action.
The topics that you can use are defined in dds_topics.yaml, and you can get more information about their data in the uORB Message Reference. For example, VehicleGlobalPosition can be used to get the vehicle global position, while VehicleCommand can be used to command actions such as takeoff and land.
The ROS 2 Example applications examples below provide concrete examples of how to use these topics.
Compatibility Issues
This section contains information that may affect how you write your ROS code.
ROS 2 Subscriber QoS Settings
ROS 2 code that subscribes to topics published by PX4 must specify a appropriate (compatible) QoS setting in order to listen to topics. Specifically, nodes should subscribe using the ROS 2 predefined QoS sensor data (from the listener example source code):
cpp
...
rmw_qos_profile_t qos_profile = rmw_qos_profile_sensor_data;
auto qos = rclcpp::QoS(rclcpp::QoSInitialization(qos_profile.history, 5), qos_profile);
subscription_ = this->create_subscription<px4_msgs::msg::SensorCombined>("/fmu/out/sensor_combined", qos,
...This is needed because the ROS 2 default Quality of Service (QoS) settings are different from the settings used by PX4. Not all combinations of publisher-subscriber Qos settings are possible, and it turns out that the default ROS 2 settings for subscribing are not! Note that ROS code does not have to set QoS settings when publishing (the PX4 settings are compatible with ROS defaults in this case).
ROS 2 & PX4 Frame Conventions
The local/world and body frames used by ROS and PX4 are different.
| Frame | PX4 | ROS |
|---|---|---|
| Body | FRD (X Forward, Y Right, Z Down) | FLU (X Forward, Y Left, Z Up) |
| World | FRD or NED (X North, Y East, Z Down) | FLU or ENU (X East, Y North, Z Up) |
TIP
See REP105: Coordinate Frames for Mobile Platforms for more information about ROS frames.
Both frames are shown in the image below (FRD on the left/FLU on the right).
The FRD (NED) conventions are adopted on all PX4 topics unless explicitly specified in the associated message definition. Therefore, ROS 2 nodes that want to interface with PX4 must take care of the frames conventions.
To rotate a vector from ENU to NED two basic rotations must be performed:
- first a pi/2 rotation around the
Z-axis (up), - then a pi rotation around the
X-axis (old East/new North).
- first a pi/2 rotation around the
To rotate a vector from NED to ENU two basic rotations must be performed:
- first a pi/2 rotation around the
Z-axis (down), - then a pi rotation around the
X-axis (old North/new East). Note that the two resulting operations are mathematically equivalent.
- first a pi/2 rotation around the
To rotate a vector from FLU to FRD a pi rotation around the
X-axis (front) is sufficient.To rotate a vector from FRD to FLU a pi rotation around the
X-axis (front) is sufficient.
Examples of vectors that require rotation are:
- all fields in TrajectorySetpoint message; ENU to NED conversion is required before sending them.
- all fields in VehicleThrustSetpoint message; FLU to FRD conversion is required before sending them.
Similarly to vectors, also quanternions representing the attitude of the vehicle (body frame) w.r.t. the world frame require conversion.
PX4/px4_ros_com provides the shared library frame_transforms to easily perform such conversions.
ROS, Gazebo and PX4 time synchronization
By default, time synchronization between ROS 2 and PX4 is automatically managed by the uXRCE-DDS middleware and time synchronization statistics are available listening to the bridged topic /fmu/out/timesync_status. When the uXRCE-DDS client runs on a flight controller and the agent runs on a companion computer this is the desired behavior as time offsets, time drift, and communication latency, are computed and automatically compensated.
For Gazebo simulations PX4 uses the Gazebo /clock topic as time source instead. This clock is always slightly off-sync w.r.t. the OS clock (the real time factor is never exactly one) and it can can even run much faster or much slower depending on the user preferences. Note that this is different from the simulation lockstep procedure adopted with Gazebo Classic.
ROS2 users have then two possibilities regarding the time source of their nodes.
ROS2 nodes use the OS clock as time source
This scenario, which is the one considered in this page and in the offboard_control guide, is also the standard behavior of the ROS2 nodes. The OS clock acts as time source and therefore it can be used only when the simulation real time factor is very close to one. The time synchronizer of the uXRCE-DDS client then bridges the OS clock on the ROS2 side with the Gazebo clock on the PX4 side. No further action is required by the user.
ROS2 nodes use the Gazebo clock as time source
In this scenario, ROS2 also uses the Gazebo /clock topic as time source. This approach makes sense if the Gazebo simulation is running with real time factor different from one, or if ROS2 needs to directly interact with Gazebo. On the ROS2 side, direct interaction with Gazebo is achieved by the ros_gz_bridge package of the ros_gz repository. Read through the repo and package READMEs to find out the right version that has to be installed depending on your ROS2 and Gazebo versions.
Once the package is installed and sourced, the node parameter_bridge provides the bridging capabilities and can be used to create an unidirectional /clock bridge:
sh
ros2 run ros_gz_bridge parameter_bridge /clock@rosgraph_msgs/msg/Clock[gz.msgs.ClockAt this point, every ROS2 node must be instructed to use the newly bridged /clock topic as time source instead of the OS one, this is done by setting the parameter use_sim_time (of each node) to true (see ROS clock and Time design).
This concludes the modifications required on the ROS2 side. On the PX4 side, you are only required to stop the uXRCE-DDS time synchronization, setting the parameter UXRCE_DDS_SYNCT to false. By doing so, Gazebo will act as main and only time source for both ROS2 and PX4.
ROS 2 Example Applications
ROS 2 Listener
The ROS 2 listener examples in the px4_ros_com repo demonstrate how to write ROS nodes to listen to topics published by PX4.
Here we consider the sensor_combined_listener.cpp node under px4_ros_com/src/examples/listeners, which subscribes to the SensorCombined message.
Build ROS 2 Workspace shows how to build and run this example.
The code first imports the C++ libraries needed to interface with the ROS 2 middleware and the header file for the SensorCombined message to which the node subscribes:
cpp
#include <rclcpp/rclcpp.hpp>
#include <px4_msgs/msg/sensor_combined.hpp>Then it creates a SensorCombinedListener class that subclasses the generic rclcpp::Node base class.
cpp
/**
* @brief Sensor Combined uORB topic data callback
*/
class SensorCombinedListener : public rclcpp::Node
{This creates a callback function for when the SensorCombined uORB messages are received (now as micro XRCE-DDS messages), and outputs the content of the message fields each time the message is received.
cpp
public:
explicit SensorCombinedListener() : Node("sensor_combined_listener")
{
rmw_qos_profile_t qos_profile = rmw_qos_profile_sensor_data;
auto qos = rclcpp::QoS(rclcpp::QoSInitialization(qos_profile.history, 5), qos_profile);
subscription_ = this->create_subscription<px4_msgs::msg::SensorCombined>("/fmu/out/sensor_combined", qos,
[this](const px4_msgs::msg::SensorCombined::UniquePtr msg) {
std::cout << "\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n";
std::cout << "RECEIVED SENSOR COMBINED DATA" << std::endl;
std::cout << "=============================" << std::endl;
std::cout << "ts: " << msg->timestamp << std::endl;
std::cout << "gyro_rad[0]: " << msg->gyro_rad[0] << std::endl;
std::cout << "gyro_rad[1]: " << msg->gyro_rad[1] << std::endl;
std::cout << "gyro_rad[2]: " << msg->gyro_rad[2] << std::endl;
std::cout << "gyro_integral_dt: " << msg->gyro_integral_dt << std::endl;
std::cout << "accelerometer_timestamp_relative: " << msg->accelerometer_timestamp_relative << std::endl;
std::cout << "accelerometer_m_s2[0]: " << msg->accelerometer_m_s2[0] << std::endl;
std::cout << "accelerometer_m_s2[1]: " << msg->accelerometer_m_s2[1] << std::endl;
std::cout << "accelerometer_m_s2[2]: " << msg->accelerometer_m_s2[2] << std::endl;
std::cout << "accelerometer_integral_dt: " << msg->accelerometer_integral_dt << std::endl;
});
}The subscription sets a QoS profile based on rmw_qos_profile_sensor_data. This is needed because the default ROS 2 QoS profile for subscribers is incompatible with the PX4 profile for publishers. For more information see: ROS 2 Subscriber QoS Settings,
The lines below create a publisher to the SensorCombined uORB topic, which can be matched with one or more compatible ROS 2 subscribers to the fmu/sensor_combined/out ROS 2 topic.
cpp
private:
rclcpp::Subscription<px4_msgs::msg::SensorCombined>::SharedPtr subscription_;
};The instantiation of the SensorCombinedListener class as a ROS node is done on the main function.
cpp
int main(int argc, char *argv[])
{
std::cout << "Starting sensor_combined listener node..." << std::endl;
setvbuf(stdout, NULL, _IONBF, BUFSIZ);
rclcpp::init(argc, argv);
rclcpp::spin(std::make_shared<SensorCombinedListener>());
rclcpp::shutdown();
return 0;
}This particular example has an associated launch file at launch/sensor_combined_listener.launch.py. This allows it to be launched using the ros2 launch command.
ROS 2 Advertiser
A ROS 2 advertiser node publishes data into the DDS/RTPS network (and hence to the PX4 Autopilot).
Taking as an example the debug_vect_advertiser.cpp under px4_ros_com/src/advertisers, first we import required headers, including the debug_vect msg header.
cpp
#include <chrono>
#include <rclcpp/rclcpp.hpp>
#include <px4_msgs/msg/debug_vect.hpp>
using namespace std::chrono_literals;Then the code creates a DebugVectAdvertiser class that subclasses the generic rclcpp::Node base class.
cpp
class DebugVectAdvertiser : public rclcpp::Node
{The code below creates a function for when messages are to be sent. The messages are sent based on a timed callback, which sends two messages per second based on a timer.
cpp
public:
DebugVectAdvertiser() : Node("debug_vect_advertiser") {
publisher_ = this->create_publisher<px4_msgs::msg::DebugVect>("fmu/debug_vect/in", 10);
auto timer_callback =
[this]()->void {
auto debug_vect = px4_msgs::msg::DebugVect();
debug_vect.timestamp = std::chrono::time_point_cast<std::chrono::microseconds>(std::chrono::steady_clock::now()).time_since_epoch().count();
std::string name = "test";
std::copy(name.begin(), name.end(), debug_vect.name.begin());
debug_vect.x = 1.0;
debug_vect.y = 2.0;
debug_vect.z = 3.0;
RCLCPP_INFO(this->get_logger(), "\033[97m Publishing debug_vect: time: %llu x: %f y: %f z: %f \033[0m",
debug_vect.timestamp, debug_vect.x, debug_vect.y, debug_vect.z);
this->publisher_->publish(debug_vect);
};
timer_ = this->create_wall_timer(500ms, timer_callback);
}
private:
rclcpp::TimerBase::SharedPtr timer_;
rclcpp::Publisher<px4_msgs::msg::DebugVect>::SharedPtr publisher_;
};The instantiation of the DebugVectAdvertiser class as a ROS node is done on the main function.
cpp
int main(int argc, char *argv[])
{
std::cout << "Starting debug_vect advertiser node..." << std::endl;
setvbuf(stdout, NULL, _IONBF, BUFSIZ);
rclcpp::init(argc, argv);
rclcpp::spin(std::make_shared<DebugVectAdvertiser>());
rclcpp::shutdown();
return 0;
}Offboard Control
For a complete reference example on how to use Offboard control with PX4, see: ROS 2 Offboard control example.
Using Flight Controller Hardware
ROS 2 with PX4 running on a flight controller is almost the same as working with PX4 on the simulator. The only difference is that you need to start both the agent and the client, with settings appropriate for the communication channel.
For more information see Starting uXRCE-DDS.
Custom uORB Topics
ROS 2 needs to have the same message definitions that were used to create the uXRCE-DDS client module in the PX4 Firmware in order to interpret the messages. The definition are stored in the ROS 2 interface package PX4/px4_msgs and they are automatically synchronized by CI on the main and release branches. Note that all the messages from PX4 source code are present in the repository, but only those listed in dds_topics.yaml will be available as ROS 2 topics. Therefore,
If you're using a main or release version of PX4 you can get the message definitions by cloning the interface package PX4/px4_msgs into your workspace.
If you're creating or modifying uORB messages you must manually update the messages in your workspace from your PX4 source tree. Generally this means that you would update dds_topics.yaml, clone the interface package, and then manually synchronize it by copying the new/modified message definitions from PX4-Autopilot/msg to its
msgfolders. Assuming that PX4-Autopilot is in your home directory~, whilepx4_msgsis in~/px4_ros_com/src/, then the command might be:shrm ~/px4_ros_com/src/px4_msgs/msg/*.msg cp ~/PX4-Autopilot/mgs/*.msg ~/px4_ros_com/src/px4_msgs/msg/Technically, dds_topics.yaml completely defines the relationship between PX4 uORB topics and ROS 2 messages. For more information see uXRCE-DDS > DDS Topics YAML.
:::
Customizing the Topic Namespace
Custom topic namespaces can be applied at build time (changing dds_topics.yaml) or at runtime (useful for multi vehicle operations):
- One possibility is to use the
-noption when starting the uxrce_dds_client from command line. This technique can be used both in simulation and real vehicles. - A custom namespace can be provided for simulations (only) by setting the environment variable
PX4_UXRCE_DDS_NSbefore starting the simulation.
Changing the namespace at runtime will append the desired namespace as a prefix to all topic fields in dds_topics.yaml. Therefore, commands like:
sh
uxrce_dds_client start -n uav_1or
sh
PX4_UXRCE_DDS_NS=uav_1 make px4_sitl gz_x500will generate topics under the namespaces:
sh
/uav_1/fmu/in/ # for subscribers
/uav_1/fmu/out/ # for publishersros2 CLI
The ros2 CLI is a useful tool for working with ROS. You can use it, for example, to quickly check whether topics are being published, and also inspect them in detail if you have px4_msg in the workspace. The command also lets you launch more complex ROS systems via a launch file. A few possibilities are demonstrated below.
ros2 topic list
Use ros2 topic list to list the topics visible to ROS 2:
sh
ros2 topic listIf PX4 is connected to the agent, the result will be a list of topic types:
/fmu/in/obstacle_distance
/fmu/in/offboard_control_mode
/fmu/in/onboard_computer_status
...Note that the workspace does not need to build with px4_msgs for this to succeed; topic type information is part of the message payload.
ros2 topic echo
Use ros2 topic echo to show the details of a particular topic.
Unlike with ros2 topic list, for this to work you must be in a workspace has built the px4_msgs and sourced local_setup.bash so that ROS can interpret the messages.
sh
ros2 topic echo /fmu/out/vehicle_statusThe command will echo the topic details as they update.
---
timestamp: 1675931593364359
armed_time: 0
takeoff_time: 0
arming_state: 1
latest_arming_reason: 0
latest_disarming_reason: 0
nav_state_timestamp: 3296000
nav_state_user_intention: 4
nav_state: 4
failure_detector_status: 0
hil_state: 0
...
---ros2 topic hz
You can get statistics about the rates of messages using ros2 topic hz. For example, to get the rates for SensorCombined:
ros2 topic hz /fmu/out/sensor_combinedThe output will look something like:
sh
average rate: 248.187
min: 0.000s max: 0.012s std dev: 0.00147s window: 2724
average rate: 248.006
min: 0.000s max: 0.012s std dev: 0.00147s window: 2972
average rate: 247.330
min: 0.000s max: 0.012s std dev: 0.00148s window: 3212
average rate: 247.497
min: 0.000s max: 0.012s std dev: 0.00149s window: 3464
average rate: 247.458
min: 0.000s max: 0.012s std dev: 0.00149s window: 3712
average rate: 247.485
min: 0.000s max: 0.012s std dev: 0.00148s window: 3960ros2 launch
The ros2 launch command is used to start a ROS 2 launch file. For example, above we used ros2 launch px4_ros_com sensor_combined_listener.launch.py to start the listener example.
You don't need to have a launch file, but they are very useful if you have a complex ROS 2 system that needs to start several components.
For information about launch files see ROS 2 Tutorials > Creating launch files
Troubleshooting
Missing dependencies
The standard installation should include all the tools needed by ROS 2.
If any are missing, they can be added separately:
colconbuild tools should be in the development tools. It can be installed using:shsudo apt install python3-colcon-common-extensionsThe Eigen3 library used by the transforms library should be in the both the desktop and base packages. It should be installed as shown:
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Additional information
- ROS 2 in PX4: Technical Details of a Seamless Transition to XRCE-DDS - Pablo Garrido & Nuno Marques (youtube)
- DDS and ROS middleware implementations