Overview

Description

A condition enables or disables one or multiple measurements to be published and thus collected. We could for example enable collecting camera images only when a robot is stopped.

Each condition is enabled or disabled through a pluginlib plugin. It has these configuration parameters.

Conditions only see forward in time

A Condition gates collection for as long as its predicate holds, giving you data from the moment it became true onward. For what happened before an event, use a Trigger instead — built from the same Condition plugins, it fires once on the false→true edge and releases a window a Measurement had already buffered.

Wiring a Condition to a Measurement

Configuring a Condition is a two-step wire-up, both under measurement_server:

Declare it in condition_plugins and give it its own named block, exactly like a Measurement — plugin names the pluginlib class, and any other keys are that Condition's own parameters.
Reference that name from a Measurement's if_all_conditions, if_any_conditions, if_none_conditions, or gate_condition (see Measurements). The Measurement is what names the Condition — nothing on the Condition side says which Measurement it gates, so one Condition can gate several Measurements at once.

The camera-only-when-stopped example above, taken from a real demo (dc_demos/params/qrcodes_stdout.yaml):

measurement_server:
  ros__parameters:
    condition_plugins: ["moving"]
    moving:
      plugin: "dc_conditions/Moving"
    right_camera:
      plugin: "dc_measurements/Camera"
      if_none_conditions: ["moving"] # collect only while NOT moving
      topic_output: "/dc/measurement/right_camera"
      cam_topic: "/right_intel_realsense_r200_depth/image_raw"

Available plugins:

Name	Description
Compare	Value of a key compares to the configured operand (eq / ne / gt / ge / lt / le / match / exists)
Robot moving	Robot is moving
Same as previous	Value of the key is the same as the previous one