.. algorithm::

.. summary::

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Description
-----------

This algorithm converts a workspace from (spectrum number, TOF) coordinates to (:math:`2\theta`, TOF). The latter view is useful for visualization and diagnostics purposes of direct geometry spectrometers with large PSD arrays. The algorithm performs the following steps:

#. Equalize the sample-to-detector distances using :ref:`ConvertToConstantL2 <algm-ConvertToConstantL2>`
#. :ref:`Rebin <algm-Rebin>` the ragged workspace to same binning over all histograms. The bin width is taken from the first bin of the first histogram. This will introduce zero padding to the histograms.
#. Mask the zero padding using :ref:`MaskNonOverlappingBins <algm-MaskNonOverlappingBins>`.
#. Group the detectors to given :math:`2\theta` bins using :ref:`GenerateGroupingPowder <algm-GenerateGroupingPowder>` and :ref:`GroupDetectors <algm-GroupDetectors>`.
#. Convert the spectrum axis from spectrum numbers to :math:`2\theta` using :ref:`ConvertSpectrumAxis <algm-ConvertSpectrumAxis>`

A default ``AngleStep`` can be defined in the :ref:`instrument parameters <InstrumentParameterFile>`. The parameter is called ``natural-angle-step``; its type should be ``float`` and value the desired ``AngleStep`` in degrees.

The instrument should have an ``l2`` parameter defined which is the nominal sample to detector distance. Also, sample logs should include a ``wavelength`` entry (in Angstroms). See :ref:`ConvertToConstantL2 <algm-ConvertToConstantL2>` for more details.

By default, the ``.xml`` and ``.par`` files generated by :ref:`GenerateGroupingPowder <algm-GenerateGroupingPowder>` are stored in a temporary location and deleted when the algorithm finishes. If these files are needed afterwards, a name for the ``.xml`` file can be given by ``GroupingFilename``. The ``.par`` file will have the same name except for the file extension which is changed from ``.xml`` to ``.par``. Note that this algorithm forces the ``.xml`` extension to ``GroupingFilename``.


Usage
-----

**Example - Applying SofTwoThetaTOF and plotting the result**

.. plot::
   :include-source:

   from mantid.simpleapi import *
   import directtools as dt
   ws = CreateSampleWorkspace(Function='Quasielastic Tunnelling', NumBanks=1, BankPixelWidth=20)
   AddSampleLog(ws, 'wavelength', '6.26', 'Number', 'Angstrom')
   SetInstrumentParameter(ws, ParameterName='l2', ParameterType='String', Value='5')
   SofTT = SofTwoThetaTOF(ws, AngleStep=1)
   fig, axes = dt.subplots()
   axes.pcolor(SofTT)
   axes.set_xlim(0.)
   # Uncomment the line below to show the plot.
   #fig.show()

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.. sourcelink::