Make Axes display use latest transform

[sloretz]

This makes the Axes display use the latest transform data, just like it did in ROS 1.

The problem with trying to get the transform at now() is the transform message was created in the past. Looking up the transform at the current time produces an error message about extrapolating into the future (assuming clocks are synchronized and the transform isn't future-dated).

To reproduce the bug this fixes:

• Start RViz and add the Axes display
• Set the "Reference Frame" to via_tf in the Axes display
• Run this python file:

from geometry_msgs.msg import TransformStamped
import rclpy
from std_msgs.msg import Header
from tf2_ros import TransformBroadcaster


def main():
    rclpy.init()

    node = rclpy.create_node("rviz_pub")
    tf_broadcast = TransformBroadcaster(node)

    while True:
        header = Header()
        header.stamp = node.get_clock().now().to_msg()
        header.frame_id = "map"

        message = TransformStamped()
        message.header = header
        message.child_frame_id = "via_tf"
        message.transform.translation.x = 0.0
        message.transform.translation.y = 0.0
        message.transform.translation.z = 0.0
        message.transform.rotation.x = 0.0
        message.transform.rotation.y = 0.0
        message.transform.rotation.z = 0.0
        message.transform.rotation.w = 1.0
        tf_broadcast.sendTransform(message)


if __name__ == "__main__":
    main()

[EricCousineau-TRI]

Woot! Just a small comment about existing docstrings.

Also, I'm surprised the ros2 docs mention a special tf2::TimePointZero, but it seems like other uses either use rclcpp::Time() or rclcpp::Time(0, 0, clock_->get_clock_type()) (as is done in FrameManager::getTransform.
https://docs.ros.org/en/humble/Tutorials/Intermediate/Tf2/Learning-About-Tf2-And-Time-Cpp.html#tf2-and-time

What is the correct things to do? I see usages of both when searching through vcs import < ros2.repos for Humble.

EDIT: Yeah, I see tf2::TimePointZero, rclcpp::Time(), and various flavors of rclcpp::Time(0, 0...)

Is there already an issue for this? If not, probably good to file.

[EricCousineau-TRI]

nit (pre-existing) Documentation for this function seems insufficient:

rviz/rviz_common/include/rviz_common/frame_manager_iface.hpp

Lines 152 to 165 in 4e976dc

	/// Return the pose for a frame relative to the fixed frame, in Ogre classes, at a given time.
	/**
	* \param[in] frame The frame to find the pose of.
	* \param[out] position The position of the frame relative to the fixed frame.
	* \param[out] orientation The orientation of the frame relative to the
	* fixed frame.
	* \return true on success, false on failure.
	*/
	virtual
	bool
	getTransform(
	const std::string & frame,
	Ogre::Vector3 & position,
	Ogre::Quaternion & orientation) = 0;

Is it possible to update that docstring to mention it's effectively using TimePointZero?

[sloretz]

Updated docs in #893

[EricCousineau-TRI]

Also, is there a way to encourage / ensure all plugins generally use the time-point-zero overload?
e.g. adding to docstring of function, "If you are writing a visualization plugin, you should prefer TimePointZero, so use this overload."

[sloretz]

Also, I'm surprised the ros2 docs mention a special tf2::TimePointZero, but it seems like other uses either use rclcpp::Time() or rclcpp::Time(0, 0, clock_->get_clock_type()) (as is done in FrameManager::getTransform.

I think there are a couple things leading to rclcpp::Time being used instead of tf2::TimePointZero. The first is RViz's FrameManager is a pluggable interface. It defaults to using tf2, but allows people to provide their own plugin to do something else. (See #346 for more info). The second is tf2 has two parts: tf2 and tf2_ros. The former has it's own time typdefs using std::chrono types, and that's where tf2::TimePointZero comes from. Anything above tf2_ros is probably using rclcpp, and so will default to using rclcpp::Time especially since tf2_ros adds APIs that use it.

Also, is there a way to encourage / ensure all plugins generally use the time-point-zero overload?

I can document that plugins without a Header should use the time-point-zero overload, and from what I can tell that seems to already be the case. Plugins operating on data with a Header will want to use the transform at the time the data was measured.

[EricCousineau-TRI]

I think there are a couple things leading to [...]

Gotcha! Is that documented somewhere discoverable on docs.ros2.org?
Also, why do some sites use rclcpp::Time(0, 0) vs. rclcpp::Time(0, 0, clock->get_clock_type())?
The latter seems more precise?

I can document that plugins [...]

Sounds good!

[sloretz]

Gotcha! Is that documented somewhere discoverable on docs.ros2.org?

RViz's Frame manager being pluggable is documented at https://index.ros.org/r/rviz/github-ros2-rviz/#pluggable-transformation-library . I didn't find any documentation for it on docs.ros2.org. It also links to an RViz plugin development guide here: https://github.com/ros2/rviz/blob/humble/docs/plugin_development.md

[sloretz]

CI (build: --packages-above-and-dependencies rviz_default_plugins test: --packages-above rviz_default_plugins)

• Linux
• Linux-aarch64
• Windows

[methylDragon]

Ok on green CI! Remember to merge this along #893 !

[EricCousineau-TRI]

thanks for the links! filed issue for time being -> #894

[sloretz]

https://github.com/Mergifyio backport humble galactic foxy

[mergify]

backport humble galactic foxy

✅ Backports have been created

• #902 Make Axes display use latest transform (backport #892) has been created for branch humble
• #903 Make Axes display use latest transform (backport #892) has been created for branch galactic
• #904 Make Axes display use latest transform (backport #892) has been created for branch foxy