.. algorithm::

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

Uses the specular reflection condition :math:`\theta_{In} \equiv \theta_{Out}` along with the Beam direction offeset to vertically shift the detectors into a corrected location.

.. math::

   2\theta = \tan^{-1}\left(\frac{UpOffset}{BeamOffset}\right)

For LineDetectors and MultiDetectors, the algorithm uses an average of
grouped detector locations to determine the detector position.

Also see
:ref:`algm-SpecularReflectionCalculateTheta`

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Usage
-----

**Example - Correct Point Detector position example**

.. testcode:: SpecularReflectionPositionCorrectExample

   # Set up an instrument so that the sample is 1.0 distance from the base of a point detector.
   import os
   instrument_def = os.path.join( config.getInstrumentDirectory() , "INTER_Definition.xml")
   ws = LoadEmptyInstrument(instrument_def)
   inst = ws.getInstrument()
   ref_frame = inst.getReferenceFrame()
   vertical_position = {ref_frame.pointingUpAxis(): 0, ref_frame.pointingAlongBeamAxis(): 1.0, ref_frame.pointingHorizontalAxis():0}
   MoveInstrumentComponent(ws, 'point-detector',RelativePosition=False, **vertical_position)
   MoveInstrumentComponent(ws, 'some-surface-holder',RelativePosition=False,  X=0, Y= 0, Z=0)

   # Correct the detector position. Has a 45 degree incident beam angle.
   corrected_ws = SpecularReflectionPositionCorrect(InputWorkspace=ws, DetectorComponentName='point-detector', AnalysisMode='PointDetectorAnalysis', TwoThetaIn=45.0, Version=1)

   # Get the detector position post correction. We expect that the vertical offset of the point detector == 1.0
   inst = corrected_ws.getInstrument()
   det_pos = inst.getComponentByName('point-detector').getPos()
   print(det_pos)

Output:

.. testoutput:: SpecularReflectionPositionCorrectExample

   [0,0.414214,1]

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