How to log data

Sometimes, information about the execution of an application like position or force values is required, e.g., for documentation or debugging. Therefore, to provide a way to log data, pitasc has already implemented multiple scripts and skills. This How-To gives you an introduction to those logging skills and scripts. Note that the skills are designed to give a simpler interface to the logging scripts for common use-cases, i.e., if you want to log positions or forces, using the skills could be simpler compared to the scripts.

In the example logging.xml, you will find multiple examples of all logging scripts and skills.

Scripts

Scripts are attached to skills and run in parallel with them. See How to attach a script to a skill.

script_measurement_logger

The script script_measurement_logger is one way to log data. It also functions as a basis for the other logging scripts and skills.

<scripts>
    <clone prototype="script_measurement_logger">
        <member id="provider" reference_id="move_skill.collections.target_to_tool.chains"/>
        <member id="file_name">{rospkg package_name}/path/{time %F_%H_%M_%S}_file_name.csv</member>
        <member id="use_simple_filter_keys">True</member>
        <member id="filter">z</member>
    </clone>
</scripts>

The member parameter provider contains a list of the data sources that provide the measurement. Either reference a list or add each data source separately, see How to set the value of a parameter. Viable data sources are:

- controllers

- kinematic_chains

- setpoint_generators

- drivers: (robot_drivers, wrench_drivers, wrench_transformer, driver_tf, cylindrical_driver, spherical_driver)

Some data sources like chains can not be referenced directly and need to be navigated to by using the . e.g. move_skill.collections.target_to_tool.chains

The parameter file_name contains the full path and name of the log-file. Non-existing directories are created. Use {} to dynamically change the path. The following artifacts are resolved

- {rospkg package_name}: Full path to package.

- {time %F_%H_%M_%S}: Current time formatted by using “std::strftime”.

The parameter use_simple_filter_keys is a bool value if true, keys in the parameter filter can be shorted by omitting the chain (e.g. ‘x’ instead of ‘target_to_tool/x’).

The parameter filter contains the names of the measurements to be logged. If left empty, every measurement is logged.

The parameter buffer_length determines the initial length of the preallocated buffer during logging. Its default value is 256. (buffer_length = #samples * (#logged_coordinates + 1))

script_error_logger

The script script_error_logger inherits from script_measurement_logger and is used to log the error inside a controller, meaning the measured value minus the desired value.

<clone prototype="script_error_logger">
    <member id="controllers" reference_id="tasks.tracking.controllers"/>
    <member id="file_name">{rospkg package_name}/path/{time %F}_file_name.csv</member>
</clone>

The parameter controllers functions as provider. Only controllers are accepted.

The parameter provider is ignored.

script_measurement_publisher

The Script script_measurement_publisher does not log data inside a file but publishes it.

<clone prototype="script_measurement_publisher">
    <member id="provider" reference_id="collections.target_to_tool.chains[0]"/>
    <member id="topic">tool_position</member>
    <member id="coordinates">x,y,z</member>
</clone>

The parameter provider references in contrast to the same parameter in script_measurement_logger only one data source that provides the measurement.

The parameter topic holds the topic name on which to publish. The default value is ‘measurements’.

Skills

Logging skills use script_measurement_logger and have access to its parameters. Use them by running them in parallel with other skills by adding the skills to the composition skill skill_concurrency.

skill_log_cartesian

The skill skill_log_cartesian logs the position and orientation of a frame in relationship to a reference frame.

<clone prototype="skill_log_cartesian">
    <member id="measured_frame">tool</member>
    <member id="reference_frame">base_link</member>
    <member id="file_name">{rospkg package_name}/path/{time %F}_file_name.csv</member>
    <member id="filter">a,b,c</member>
</clone>

The parameter measured_frame holds the id of the frame which data is logged.

The parameter reference_frame holds the id of the reference frame for the logged cartesian data.

The parameters provider and use_simple_filter_keys of script_measurement_logger are already set and can not be accessed.

skill_log_force

The skill skill_log_force logs the force and torque in a desired frame.

<clone prototype="skill_log_force">
    <member id="force_frame">tool</member>
    <member id="file_name">{rospkg package_name}/path/{time %F}_file_name.csv</member>
    <member id="filter">x,y,z</member>
</clone>

The parameter force_frame holds the id of the frame defining the desired position and axes for measuring force and torque.

The parameters provider and use_simple_filter_keys of script_measurement_logger are already set and can not be accessed.