.. _ALFView-ref: ALFView ======= .. image:: ../../images/ALFView_Interface.PNG :align: right :height: 400px .. contents:: Table of Contents :local: .. |export| image:: /images/icons/download.png .. |externalplot| image:: /images/icons/open-in-new.png .. |reset| image:: /images/icons/replay.png Interface Overview ------------------ The ALF instrument requires frequent manual adjustments after each run to realign the single crystal(s). These adjustments require us to know how much we should rotate the sample by (:code:`R`). This can be calculated from the out of plane angle, :code:`V`, and two theta, :code:`2θ`, obtained from the ALFView interface. .. math:: R = V / (2\sin(\theta)) The Out of Plane Angle is the vertical position of the detectors as viewed from the sample. The interface can be accessed from the main menu of MantidWorkbench, in *Interfaces → Direct → ALFView*. Loading Data ------------ The loading section is used to load a Sample dataset, and optionally a Vanadium dataset. This can be achieved by either typing the run number or browsing to the file of interest. The Sample and Vanadium datasets are first :ref:`normalised by current ` and then converted to units of dSpacing. The Sample is then normalised by dividing it by the Vanadium (if a Vanadium run is provided). Note that the Sample and Vanadium x arrays must be the same for this normalisation to work. Selecting Tubes --------------- The normalised data should now be plotted on a custom version of the :ref:`Instrument View `, which only contains the 'Render' and 'Pick' tabs. In the 'Pick' tab, you have several options for selecting one or more tubes. +----------------------------------------+-----------------------------------------------------------+ | Tool | Effect | +========================================+===========================================================+ | Select whole tube | Select a tube by clicking on it. Click on more than one | | | tube to select multiple. This tool remains selected | | | until you click a different tool in the 'Pick' tab. | +----------------------------------------+-----------------------------------------------------------+ | Draw a rectangle | Select one or more tubes by drawing a rectangular region. | | | If any part of a tube, no matter how small, is contained | | | within the region, it is selected. The Edit Shape tool is | | | selected after this has been used. | +----------------------------------------+-----------------------------------------------------------+ | Edit a shape | Allows you to select a shape drawn on the plot so you can | | | move, resize or delete it. Use the ``Delete`` key to | | | delete the selected shape. | +----------------------------------------+-----------------------------------------------------------+ The following keyboard shortcuts are available when a shape is selected. +-----------------------------+---------------------------------------+ | Shortcut | Action | +=============================+=======================================+ |``Ctrl+C`` | Copies the selected shape(s) | +-----------------------------+---------------------------------------+ |``Ctrl+V`` | Pastes the selected shape(s) | +-----------------------------+---------------------------------------+ |``Delete`` | Deletes the selected shape(s) | +-----------------------------+---------------------------------------+ Once you have selected a tube, a plot of the out of plane angle vs counts is plotted on the right hand side of the interface. Calculating Rotation -------------------- At the top of the right hand pane is a preview plot showing the out of plane angle vs counts for the selected tubes. A Fit of a Flat Background + Gaussian composite function is required to determine the centre of the peak on this plot. Above the plot are several options which are not necessary for the main workflow. +----------------------------------------+-------------------------------------------------------------------------------------------------+ | Option | Description | +========================================+=================================================================================================+ | |export| Generate workspace from plot | This option will export the data displayed on the plot to a workspace named 'ALFView_exported'. | +----------------------------------------+-------------------------------------------------------------------------------------------------+ | |externalplot| Open plot in new window | This option will open the plot in a separate window. This provides more plotting options. | +----------------------------------------+-------------------------------------------------------------------------------------------------+ | |reset| Reset extracted plot | This option will remove the Fit on the plot and reset the peak centre and rotation angle. | +----------------------------------------+-------------------------------------------------------------------------------------------------+ Underneath the plot are the following values. +------------------------------+-----------------------------------------------------------------------------------+ | Value | Description | +==============================+===================================================================================+ | Two theta, :code:`2θ` | The average two theta of the extracted tubes, in degrees. The two theta of a tube | | | is taken to be the two theta at which the out of plane angle is closest to zero. | +------------------------------+-----------------------------------------------------------------------------------+ | Fit range | The range within which the fit should be performed, in degrees. | +------------------------------+-----------------------------------------------------------------------------------+ | Peak centre, :code:`V` | The centre of a Flat Background + Gaussian composite function, in degrees. | +------------------------------+-----------------------------------------------------------------------------------+ | Rotation angle, :code:`R` | The rotation angle defined by the equation above, in units of degrees. | +------------------------------+-----------------------------------------------------------------------------------+ Click on the `Fit` button to find a value for the peak centre. Repeated Fits will attempt to refine the Peak Centre value further. The resulting fit is added to the preview plot. The Rotation angle, :code:`R`, will also be calculated automatically in units of degrees. .. categories:: Interfaces Direct