tf2_ros::StaticTransformBroadcaster does not keep last msg for later subscription

[sharronliu]

Bug report

Required Info:

• Operating System:
  • Ubuntu 18.04
• Installation type:
  • binaries
• Version or commit hash:
  • Dashing
• DDS implementation:
  • Fast-RTPS
• Client library (if applicable):
  • rclcpp

Steps to reproduce issue

In rclcpp node, send static TF using tf2_ros::StaticTransformBroadcaster::sendTransform(). The function was invoked only once, since the TF is unchanged. The observation is the msg was not received by a later subscription. This behavior differs from ROS1.
Try to instanciate the rclcpp node with below QoS profile, problem still observed.

• rclcpp::Qos(rclcpp::KeepLast(1))
• rclcpp::Qos(rclcpp::KeepLast(10))
• rclcpp::Qos(rclcpp::KeepAll())

Please can you suggest any other parameters may lead to the problematic result?

Expected behavior

The static msg was kept for later subscription

Actual behavior

The static msg was not received in later subscription

[clalancette]

It is kept, but the naming in DDS (and hence ROS 2) is different. In ROS 2, a "latched" topic is called "transient local". If the publisher is a "transient local", then it will hold a copy for any subscriber that comes in later. However, the subscriber must also be "transient local" for this to work.

If you use the stock TF2 clients, they have the appropriate QoS settings for this to work. If you are subscribing to tf_static on your own, you'll need to set the transient_local QoS setting.

I'm going to close this out assuming that is what is going on here, but feel free to keep commenting or re-open if this doesn't work for you.

[sloretz]

@sharronliu I noticed you're using Dashing. The static listener and broadcaster use transient local durability as of #160, so it should behave as you expect in Eloquent.