ROS2极简总结-坐标变换-TF

zhangrelay

发布于 2021-12-02 13:01:14

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发布于 2021-12-02 13:01:14

文章被收录于专栏：机器人课程与技术机器人课程与技术

参考：

TF2 - TRANSFORMS IN ROS2
ROS机器人TF基础（坐标相关概念和实践）

TF2 - 概述

TF2 是 TF (TransForm) 库的第二代。事实上，ROS1 中的 TF 目前在后台调用 TF2。 ROS2 仅使用 TF2。
TF2 跟踪树结构中的所有坐标系。
与 ROS2 中的大多数功能一样，TF2 API 仍在开发中，但基本功能已经可用。
TF2 vs TF - 更快、更高效、新功能和更容易扩展。

*此处重点，ROS1成熟，而ROS2还是深度开发中的实验版，LTS长期支持版目前也没有5年，而是3年，此版本不适合初学者学习！

rviz2中可视化

rqt_tf_tree

设计

TF2 核心独立于 ROS & BufferCore 类提供 API

时间同步

用户可以查询任意给定时间点树中任意 2 帧之间的转换 - 即使在过去！
- 对于异步/分布式系统必不可少

广播

提供坐标之间的转换（动态/静态）。

例如：robot_state_publisher 提供基于 URDF 的 TF 数据
例如：用户编写的具有专用广播器的节点

监听

可以访问变换树并查找 2 帧之间的特定变换（阻塞/非阻塞）。

buffer = tf2_ros.Buffer()
transform = buffer.lookup_transform("base_link","camera_link", rclpy.time.Time()) # Blocking
transform = await buffer.lookup_transform_async("base_link","camera_link",rclpy.time.Time())  #Non-Blocking

函数原型：lookup_transform(target_frame,source_frame,time)

使用 rclpy.time.Time() 提供最新的可用转换。

工具：

tf2_ros buffer_server.exe tf2_ros static_transform_publisher.exe tf2_ros tf2_echo.exe tf2_ros tf2_monitor.exe tf2_tools view_frames.py

ros2 launch dummy_robot_bringup dummy_robot_bringup.launch.py 

rviz2

发布坐标变换数据

ros2 run tf2_ros static_transform_publisher 1 2 3 0.5 0.1 -1.0 foo bar

接受坐标变换数据

ros2 run tf2_ros tf2_echo foo bar

数据：

[INFO] [1628841444.349748000] [tf2_echo]: Waiting for transform foo ->  bar: Invalid frame ID "foo" passed to canTransform argument target_frame - frame does not exist
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]
At time 0.0
- Translation: [1.000, 2.000, 3.000]
- Rotation: in Quaternion [-0.475, -0.076, 0.240, 0.843]

ros2 run tf2_ros tf2_monitor
Gathering data on all frames for 10 seconds...



RESULTS: for all Frames

Frames:
Frame: bar, published by <no authority available>, Average Delay: 336.186, Max Delay: 336.186
Frame: single_rrbot_camera_link, published by <no authority available>, Average Delay: 0.0112712, Max Delay: 0.0168042
Frame: single_rrbot_hokuyo_link, published by <no authority available>, Average Delay: 0.011265, Max Delay: 0.016798
Frame: single_rrbot_link1, published by <no authority available>, Average Delay: 0.0112664, Max Delay: 0.0167992
Frame: single_rrbot_link2, published by <no authority available>, Average Delay: 0.0197751, Max Delay: 0.0335286
Frame: single_rrbot_link3, published by <no authority available>, Average Delay: 0.0197761, Max Delay: 0.033529

All Broadcasters:
Node: <no authority available> 34.0131 Hz, Average Delay: 0.940838 Max Delay: 336.186



RESULTS: for all Frames

Frames:
Frame: bar, published by <no authority available>, Average Delay: 336.186, Max Delay: 336.186
Frame: single_rrbot_camera_link, published by <no authority available>, Average Delay: 0.0111137, Max Delay: 0.0169733
Frame: single_rrbot_hokuyo_link, published by <no authority available>, Average Delay: 0.0111072, Max Delay: 0.0169675
Frame: single_rrbot_link1, published by <no authority available>, Average Delay: 0.0111086, Max Delay: 0.0169683
Frame: single_rrbot_link2, published by <no authority available>, Average Delay: 0.0197954, Max Delay: 0.0335286
Frame: single_rrbot_link3, published by <no authority available>, Average Delay: 0.0197964, Max Delay: 0.033529

ros2 run tf2_tools view_frames.py