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