| Derived Measurements |
| ===================== |
| |
| |
| The ``DerivedMeasurements`` API provides a consistent way of performing post |
| processing on a provided :class:`MeasurementCsv` file. |
| |
| Example |
| ------- |
| |
| The following example shows how to use an implementation of a |
| :class:`DerivedMeasurement` to obtain a list of calculated ``DerivedMetric``'s. |
| |
| .. code-block:: ipython |
| |
| # Import the relevant derived measurement module |
| # in this example the derived energy module is used. |
| In [1]: from devlib import DerivedEnergyMeasurements |
| |
| # Obtain a MeasurementCsv file from an instrument or create from |
| # existing .csv file. In this example an existing csv file is used which was |
| # created with a sampling rate of 100Hz |
| In [2]: from devlib import MeasurementsCsv |
| In [3]: measurement_csv = MeasurementsCsv('/example/measurements.csv', sample_rate_hz=100) |
| |
| # Process the file and obtain a list of the derived measurements |
| In [4]: derived_measurements = DerivedEnergyMeasurements.process(measurement_csv) |
| |
| In [5]: derived_measurements |
| Out[5]: [device_energy: 239.1854075 joules, device_power: 5.5494089227 watts] |
| |
| API |
| --- |
| |
| Derived Measurements |
| ~~~~~~~~~~~~~~~~~~~~ |
| |
| .. class:: DerivedMeasurements |
| |
| The ``DerivedMeasurements`` class provides an API for post-processing |
| instrument output offline (i.e. without a connection to the target device) to |
| generate additional metrics. |
| |
| .. method:: DerivedMeasurements.process(measurement_csv) |
| |
| Process a :class:`MeasurementsCsv`, returning a list of |
| :class:`DerivedMetric` and/or :class:`MeasurementsCsv` objects that have been |
| derived from the input. The exact nature and ordering of the list memebers |
| is specific to indivial 'class'`DerivedMeasurements` implementations. |
| |
| .. method:: DerivedMeasurements.process_raw(\*args) |
| |
| Process raw output from an instrument, returnin a list :class:`DerivedMetric` |
| and/or :class:`MeasurementsCsv` objects that have been derived from the |
| input. The exact nature and ordering of the list memebers is specific to |
| indivial 'class'`DerivedMeasurements` implewmentations. |
| |
| The arguents to this method should be paths to raw output files generated by |
| an instrument. The number and order of expected arguments is specific to |
| particular implmentations. |
| |
| |
| Derived Metric |
| ~~~~~~~~~~~~~~ |
| |
| .. class:: DerivedMetric |
| |
| Represents a metric derived from previously collected ``Measurement``s. |
| Unlike, a ``Measurement``, this was not measured directly from the target. |
| |
| |
| .. attribute:: DerivedMetric.name |
| |
| The name of the derived metric. This uniquely defines a metric -- two |
| ``DerivedMetric`` objects with the same ``name`` represent to instances of |
| the same metric (e.g. computed from two different inputs). |
| |
| .. attribute:: DerivedMetric.value |
| |
| The ``numeric`` value of the metric that has been computed for a particular |
| input. |
| |
| .. attribute:: DerivedMetric.measurement_type |
| |
| The ``MeasurementType`` of the metric. This indicates which conceptual |
| category the metric falls into, its units, and conversions to other |
| measurement types. |
| |
| .. attribute:: DerivedMetric.units |
| |
| The units in which the metric's value is expressed. |
| |
| |
| Available Derived Measurements |
| ------------------------------- |
| |
| .. note:: If a method of the API is not documented for a particular |
| implementation, that means that it s not overriden by that |
| implementation. It is still safe to call it -- an empty list will be |
| returned. |
| |
| Energy |
| ~~~~~~ |
| |
| .. class:: DerivedEnergyMeasurements |
| |
| The ``DerivedEnergyMeasurements`` class is used to calculate average power and |
| cumulative energy for each site if the required data is present. |
| |
| The calculation of cumulative energy can occur in 3 ways. If a |
| ``site`` contains ``energy`` results, the first and last measurements are extracted |
| and the delta calculated. If not, a ``timestamp`` channel will be used to calculate |
| the energy from the power channel, failing back to using the sample rate attribute |
| of the :class:`MeasurementCsv` file if timestamps are not available. If neither |
| timestamps or a sample rate are available then an error will be raised. |
| |
| |
| .. method:: DerivedEnergyMeasurements.process(measurement_csv) |
| |
| This will return total cumulative energy for each energy channel, and the |
| average power for each power channel in the input CSV. The output will contain |
| all energy metrics followed by power metrics. The ordering of both will match |
| the ordering of channels in the input. The metrics will by named based on the |
| sites of the coresponding channels according to the following patters: |
| ``"<site>_total_energy"`` and ``"<site>_average_power"``. |
| |