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TF remapper (more efficient and versatile C++ version)

This package is an alternative to official ROS node tf/tf_remap with the following advantages:

• Works natively with TF2

  • that could probably save a few data conversions

• Performance: handles tens of TF subscribers with thousands of TF messages/sec with ease

  • the official node fully utilizes 2 i7 CPU cores if you have 10 subscribers and publish 2000 TF messages per second (ros/geometry#175)

  • this package needs about 0.4 CPU cores for the same

• Can also remap /tf_static

  • the official package can not do that correctly

• Can also remove frames (if you pass empty string to new)

  • this can come handy if you e.g. want to recompute your map in bagfiles using a brand new algorithm

• Can work in both ways

  • not only taking frames published on /tf_old and remapping and publishing them to /tf, but it can also watch /tf, perform a reverse remapping, and publish new TF messages to /tf_old

  • this can come handy if you e.g. want to run your robot in a restricted world where it does not know about the other robots (it has its own /map frame), and then you have a multirobot coordination algorithm which wants to see the maps of each robot as /ugv1/map, /ugv2/map and so on, and also wants to publish a /global_map frame available to all robots.

• Backwards compatible with tf/tf_remap

  • to use this remapper, just change package name from tf to tf_remapper_cpp in your launch files

  • all the new functionality should not endanger the basic usage, since the package is accompanied by an exhaustive test suite

• API Documentation and usage examples

• the remapping logic is available in dynamic library libtf_remapper_cpp.so, class TfRemapper

It is possible that in the future this implementation will become the default one in ROS.

Nodes

tf_remapper_cpp/tf_remap

The node that performs the TF remapping.

Private parameters

• mappings (array of dicts): The rules for TF frame name remapping, e.g. [{"old": "b", "new": "d"}]. Each dict presents one remapping rule. Each dict contains keys old and new. If either of these keys is missing or its value is empty string, it means the TF frame should be deleted.

  • Until ros/ros_comm#1498 is fixed, you can not pass this parameter from rosrun commandline - either set it in a launch file, or use rosparam set /tf_remapper/mappings '[{"old": "b", "new": "d"}]' before launching this node.

• static_tf (bool): Whether the remapper acts on static TFs or not. If not set, it is autodetected from new_tf_topic_name parameter.

  • Static TFs need special handling, so be sure to have this parameter set correctly, otherwise it can cause performance issues (when used with non-static TFs) or incorrect operation (if not used with static TFs).

  • Autodetection checks if the new_tf_topic_name is tf_static or /tf_static, and if it is, then static_tf is set to True, otherwise it is set to False.

• old_tf_topic_name (string, default '/tf_old'): The topic on which old TFs are subscribed.

• new_tf_topic_name (string, default '/tf'): The topic on which remapped TFs are published.

• is_bidirectional (bool, default False): If True, the remapper will also allow passing TFs published on the "remapped end" to the "old end" via a reverse mapping.

  • Pay special attention if you use any kind of multimaster solution or a custom topic transport. This node needs CallerIDs to be unchanged. If this contract is broken, the node will probably enter an infinite loop reacting to its own published messages.

Subscribed topics

• /tf_old (or any other topic set in old_tf_topic_name; type tf2_ros/TFMessage): The original TF messages that are to be remapped.

• /tf (or any other topic set in new_tf_topic_name; only if is_bidirectional == True; type tf2_ros/TFMessage): The TF messages with remapped frames. If some node publises to this topic and this remapper is running in bidirectional mode, it sends the newly published transforms back to /tf_old.

Published topics

• /tf (or any other topic set in new_tf_topic_name; type tf2_ros/TFMessage): The TF messages with remapped frames.

• /tf_old (or any other topic set in old_tf_topic_name; only if is_bidirectional == True; type tf2_ros/TFMessage): The original TF messages. If some node publises to /tf and this remapper is running in bidirectional mode, it sends the newly published transforms back to this topic.

Example usage in launch files

simple.launch

<launch>
    <group>
        <remap from="tf" to="tf_old" />
        <!-- The tf(1) static_transform_publisher does not use /tf_static, but periodically publises to /tf -->
        <node name="broadcaster_ab" pkg="tf" type="static_transform_publisher" args="1 2 3 4 5 6 a b 10"/>
        <!-- Usually, there would be e.g. a rosbag play instead of the static tf publisher. -->
    </group>

    <node name="remapper" pkg="tf_remapper_cpp" type="tf_remap">
        <rosparam param="mappings">[{old: b, new: c}]</rosparam>
    </node>

    <!-- This node will see transform a->c -->
    <node name="my_node" pkg="my_pkg" type="node_type" />
</launch>

static_tf.launch

<launch>
    <group>
        <remap from="tf_static" to="tf_static_old" />
        <!-- The tf2 static_transform_publisher uses /tf_static -->
        <node name="broadcaster_ab" pkg="tf2_ros" type="static_transform_publisher" args="1 2 3 4 5 6 a b"/>
        <!-- Usually, there would be e.g. a rosbag play instead of the static tf publisher. -->
    </group>

    <node name="remapper" pkg="tf_remapper_cpp" type="tf_remap">
        <rosparam param="mappings">[{old: b, new: c}]</rosparam>
        <!--<param name="static_tf" value="true" />  - this is not needed, autodetection works in this case -->
    </node>

    <!-- This node will see static transform a->c -->
    <node name="my_node" pkg="my_pkg" type="node_type" />
</launch>

bidirectional.launch

<launch>
    <group>
        <remap from="tf" to="tf_old" />
        <!-- The tf(1) static_transform_publisher does not use /tf_static, but periodically publises to /tf -->
        <node name="broadcaster_ab" pkg="tf" type="static_transform_publisher" args="1 2 3 4 5 6 a b 10"/>
        <!-- Usually, there would be e.g. a rosbag play instead of the static tf publisher. -->
            
        <!-- This node will see transforms a->b and d->e -->
        <node name="my_node2" pkg="my_pkg" type="node_type" />
    </group>

    <node name="remapper" pkg="tf_remapper_cpp" type="tf_remap">
        <rosparam param="mappings">[{old: b, new: c}, {old: e, new: f}]</rosparam>
        <param name="is_bidirectional" value="true" />
    </node>

    <!-- This node will see transforms a->c and d->f -->
    <node name="my_node" pkg="my_pkg" type="node_type" />
        
    <node name="broadcaster_df" pkg="tf" type="static_transform_publisher" args="1 2 3 4 5 6 d f 10"/>
</launch>