iory commented 2 years ago

What is this?

rostopic echo has a filter function, but it cannot publish a topic. topic_tools/transform can format a topic and publish it, but it does not have the ability to filter. Transforming while filtering a topic is simple and powerful. This node provides a filter and publish (i.e. relay) functions.

Subscribing Topic

~input (rospy/AnyMsg)

Input message.

Publishing Topic

~output (~output_type)

Output topic. You can specify ~output_type param to publish topic.

Parameters

~output_type (String, required)

Message type of output_topic like std_msgs/Float32. This is the input for the get_message_class function.
~filter (String, default: None)

Condition of messages that match a specified Python expression.

The Python expression can access any of the Python builtins plus: topic (the topic of the message), m (the message) and t (time of message).

For example, ~input topic is std_msgs/String and if you want to check whether a sentence is a hello, you can do the following.

filter: m.data == 'hello'

Note that, use escape sequence when using the following symbols <(<), >(>), &(&), '(') and "(") in launch file.

~transform (String, default: m)

Python expression that transform the input messages, which are given in the variable m. The default expression is m, which results in forwarding input (which can be a topic field) into output_topic.
~import (List[String], default: [])

List of Python modules to import and use in the expression.

Usage

$ rosrun jsk_topic_tools filtered_relay.py ~input:=/right_endeffector/wrench \
    ~output:=/right_endeffector/force_norm \
    _filter:='numpy.linalg.norm([m.wrench.force.x, m.wrench.force.y, m.wrench.force.z]) > 10.0' \
    _output_type:=geometry_msgs/WrenchStamped _import:="[geometry_msgs, numpy]"

Example

The following example subscribe to /right_endeffector/wrench and only those with a force norm greater than 10 are published as /right_endeffector/force_norm.

roslaunch jsk_topic_tools sample_filtered_relay.launch

Use case

https://github.com/jsk-ros-pkg/jsk_robot/pull/1570

k-okada commented 2 years ago

since https://github.com/jsk-ros-pkg/jsk_robot/pull/1570 has been closed and currently we do not have usage for this node. So may be we can leave this PR and re-start discussion / review until we found another use cases.