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TransformBroadcaster as member of ROS2 Node

asked 2018-09-23 08:40:41 -0600

Christian Rauch gravatar image

What is the proper way to create a tf2_ros::TransformBroadcaster inside a rclcpp::Node?

I am trying to create a TransformBroadcaster as a member of a ROS2 node, i.e. constructing from this. So far, I am constructing the ROS2 node member tf_broadcaster from a shared pointer to this:

MyNode::MyNode() : Node("my_node", "node_namespace", true) {
    // in header: std::unique_ptr<tf2_ros::TransformBroadcaster> tf_broadcaster;
    tf_broadcaster = std::make_unique<tf2_ros::TransformBroadcaster>(rclcpp::Node::SharedPtr(this));
}

This seems to work in general, e.g. I can publish my transforms. However, I get a double free corruption error when the node is deconstructed, because the node is deconstructed a second time when shared_ptr goes out of scope.

Neither this->shared_from_this() (error at construction: terminate called after throwing an instance of 'std::bad_weak_ptr') nor std::shared_ptr<rclcpp::Node>(this) (error at deconstruction: free(): invalid pointer) allow me to create a shared pointer of this.

Wouldn't it be easier, if the rclcpp::Node would inherit the transformer methods from a TransformBroadcaster class instead of instantiating it manually? E.g. class MyNode : public rclcpp::Node, tf2_ros::TransformBroadcaster {} and then just call this->sendTransform(tf);.

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Comments

I had a TransformBroadcaster member variable that couldn't be constructed from shared_from_this at container class construction time, so I made it a shared ptr and initialized that later, which appeared to function but ctrl-c wouldn't kill the node properly (two ctrl-c in a row would work)

lucasw gravatar image lucasw  ( 2018-12-03 11:24:16 -0600 )edit

weak_ptr would break the cyclical shared_ptr there.

lucasw gravatar image lucasw  ( 2018-12-03 21:36:56 -0600 )edit

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answered 2018-09-24 18:04:18 -0600

Christian Rauch gravatar image

updated 2020-09-07 19:09:10 -0600

A workaround would be to simply create the publisher for tf2_msgs::msg::TFMessage on "/tf" manually like this:

#include <tf2_msgs/msg/tf_message.hpp>
...
rclcpp::Publisher<tf2_msgs::msg::TFMessage>::SharedPtr pub_tf;
...
rmw_qos_profile_t tf_qos_profile = rmw_qos_profile_default;
tf_qos_profile.depth = 100;
pub_tf = this->create_publisher<tf2_msgs::msg::TFMessage>("/tf", tf_qos_profile);
tf2_msgs::msg::TFMessage tfs;
geometry_msgs::msg::TransformStamped tf;
// set tf.transform
tfs.transforms.push_back(tf);
// optionally add multiple TransformStamped to tfs.transforms
pub_tf->publish(tfs);

For now, the implementation of TransformBroadcaster is basically doing the same.

Edit: At least with foxy, it is possible to initialise the TransformBroadcaster as intended:

class MultiWiiNode : public rclcpp::Node {
  tf2_ros::TransformBroadcaster tf_broadcaster;
}

MyNode::MyNode() : Node("my_node"), tf_broadcaster(this) { }
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I had strange behavior in bouncy with StaticTransformBroadcaster (including problems kill the node with ctrl-c and 'invalid start byte' messages from launch.LaunchService), switched to TFMessage publication and now am avoiding those issues.

lucasw gravatar image lucasw  ( 2018-12-03 12:49:45 -0600 )edit
0

answered 2018-09-24 14:45:00 -0600

William gravatar image

updated 2018-09-24 14:49:22 -0600

You cannot use a shared pointer to this in the constructor. You should use this->shared_from_this() but you cannot do that in the constructor.

You could try creating the tf_broadcaster on the first time you use it (store nullptr until then).

Also, ideally the tf2_ros::TransformBroadcaster would take some of the node interfaces, allowing you to pass them in the constructor.

EDIT: with respect to your suggestion...

Wouldn't it be easier, if the rclcpp::Node would inherit the transformer methods from a TransformBroadcaster class instead of instantiating it manually? E.g. class MyNode : public rclcpp::Node, tf2_ros::TransformBroadcaster {} and then just call this->sendTransform(tf);.

That doesn't resolve the issue because the tf2_ros::TransformBroadcaster still needs to access the node, so you'd need to delegate to the constructor for it during the member initialization (e.g. class MyNode : public rclcpp::Node, tf2_ros::TransformBroadcaster : rclcpp::Node(...), tf2_ros::TransformBroadcaster(this) {}) and that requires that you pass this, just like you have the issue now.

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Maybe templating TransformBroadcaster could solve the problem? The TransformBroadcaster does not actually need to store a pointer to the node, only the publisher. It could be constructed from a reference or raw pointer like TransformBroadcaster(T* node) { node->create_publisher(); }.

Christian Rauch gravatar image Christian Rauch  ( 2018-09-24 18:09:34 -0600 )edit

Yeah, that could also work.

William gravatar image William  ( 2018-09-24 18:10:48 -0600 )edit

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Asked: 2018-09-23 08:40:41 -0600

Seen: 1,324 times

Last updated: Sep 07 '20