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SpecularReflectionPositionCorrect v2

Summary

Corrects a reflectometer’s detector component’s position.

See Also

SpecularReflectionCalculateTheta, FindReflectometryLines

Properties

Name	Direction	Type	Default	Description
InputWorkspace	Input	MatrixWorkspace	Mandatory	An input workspace to correct.
TwoTheta	Input	number	Optional	Angle used to correct the detector component [degrees].
DetectorCorrectionType	Input	string	VerticalShift	Whether detectors should be shifted vertically or rotated around the sample position. Allowed values: [‘VerticalShift’, ‘RotateAroundSample’]
DetectorComponentName	Input	string		Name of the detector component to correct, for example point-detector
DetectorID	Input	number	Optional	The ID of the detector to correct; if both the component name and the detector ID are set the latter will be used.
SampleComponentName	Input	string	some-surface-holder	Name of the sample component; if the given name is not found in the instrument, the default sample is used.
OutputWorkspace	Output	MatrixWorkspace	Mandatory	A workspace with corrected detector position.
DetectorFacesSample	Input	boolean	False	If true, a normal vector at the centre of the detector always points towards the sample.
LinePosition	Input	number	Optional	A fractional workspace index for the specular line centre.
PixelSize	Input	number	Optional	Size of a detector pixel, in metres.
MoveFixedDetectors	Input	boolean	False	Whether to change the position of individual detector pixels located within a structured bank. If set to false then a request to change the position of a detector pixel within a structured bank will be ignored. The default value for this property is set to false to maintain backwards compatibility.

Description

Moves the specified detector component to a given angle between the beam and the sample-to-detector vector. The detector component is moved as a block. The rest of the instrument components remain in original positions. The component can be shifted vertically (default), or rotated around the sample position. When rotating around the sample, an optional rotation can be applied so that the detector always faces the sample.

In the most basic operation, the detector is moved to the angle specified by TwoTheta. This case is schematically shown below for rotation around the sample position and DetectorFacesSample set to True.

If LinePosition and PixelSize are also given, the detector will be moved such that the angle will be TwoTheta for the pixel at workspace index LinePosition. Note that LinePosition can be a fractional index making it possible to adjust the detector angle to a fitted line position. The figure below illustrates this option.

Note

The line positions can be acquired by using, for instance, FindReflectometryLines.

Previous Versions

For version 1 of the algorithm, please see SpecularReflectionPositionCorrect-v1.

Usage

Note

To run these usage examples please first download the usage data, and add these to your path. In Mantid this is done using Manage User Directories.

Example - Correct ‘point-detector’

print('point-detector')
polref = Load(Filename=r'POLREF00004699.raw', PeriodList=1)
polref = polref[0]

instr = polref.getInstrument()
print('Original position: ' + str(instr.getComponentByName('point-detector').getPos()))

polref_vert = SpecularReflectionPositionCorrect(polref, TwoTheta = 2*0.49, DetectorComponentName='point-detector', DetectorCorrectionType='VerticalShift')
instr = polref_vert.getInstrument()
print('Vertical shift:    ' + str(instr.getComponentByName('point-detector').getPos()))

polref_rot = SpecularReflectionPositionCorrect(polref, TwoTheta = 2*0.49, DetectorComponentName='point-detector', DetectorCorrectionType='RotateAroundSample')
instr = polref_rot.getInstrument()
print('Rotated:           ' + str(instr.getComponentByName('point-detector').getPos()))

Output:

Note that in this case the difference between shifting the detectors vertically or rotating them is negligible.

point-detector
Original position: [...,...,...]
Vertical shift:    [...,...,...]
Rotated:           [...,...,...]

Example - Correct ‘lineardetector’

print('lineardetector')
polref = Load(Filename=r'POLREF00004699.raw', PeriodList=1)
polref = polref[0]

instr = polref.getInstrument()
print('Original position: ' + str(instr.getComponentByName('lineardetector').getPos()))

polref_vert = SpecularReflectionPositionCorrect(polref, TwoTheta = 2*0.49, DetectorComponentName='lineardetector')
instr = polref_vert.getInstrument()
print('Vertical shift:    ' + str(instr.getComponentByName('lineardetector').getPos()))

polref_rot = SpecularReflectionPositionCorrect(polref, TwoTheta = 2*0.49, DetectorComponentName='lineardetector', DetectorCorrectionType='RotateAroundSample')
instr = polref_rot.getInstrument()
print('Rotated:           ' + str(instr.getComponentByName('lineardetector').getPos()))

Output:

lineardetector
Original position: [...,...,...]
Vertical shift:    [...,...,...]
Rotated:           [...,...,...]

Example - Correct ‘OSMOND’

print('OSMOND')
polref = Load(Filename=r'POLREF00004699.raw', PeriodList=1)
polref = polref[0]

instr = polref.getInstrument()
print('Original position: ' + str(instr.getComponentByName('OSMOND').getPos()))

polref_vert = SpecularReflectionPositionCorrect(polref, TwoTheta = 2*0.49, DetectorComponentName='OSMOND')
instr = polref_vert.getInstrument()
print('Vertical shift:    ' + str(instr.getComponentByName('OSMOND').getPos()))

polref_rot = SpecularReflectionPositionCorrect(polref, TwoTheta = 2*0.49, DetectorComponentName='OSMOND', DetectorCorrectionType='RotateAroundSample')
instr = polref_rot.getInstrument()
print('Rotated:           ' + str(instr.getComponentByName('OSMOND').getPos()))

Output:

OSMOND
Original position: [...,...,...]
Vertical shift:    [...,...,...]
Rotated:           [...,...,...]

Example - Rotate given pixel

import numpy
# We'll just use an empty workspace here.
ws = LoadEmptyInstrument(InstrumentName='D17')
# Get rid of monitors
ExtractMonitors(ws, DetectorWorkspace='ws')
ws = mtd['ws']
line_position = 22.
spectrum_info = ws.spectrumInfo()
two_theta = numpy.rad2deg(spectrum_info.twoTheta(int(line_position)))
print('Pixel {} 2theta'.format(int(line_position)))
print('before angle correction: {:.3}'.format(two_theta))
ws = SpecularReflectionPositionCorrect(
    ws,
    TwoTheta=1.5,
    DetectorCorrectionType='RotateAroundSample',
    DetectorComponentName='detector',
    DetectorFacesSample=True,
    LinePosition=line_position,
    PixelSize=0.001195)
spectrum_info = ws.spectrumInfo()
two_theta = numpy.rad2deg(spectrum_info.twoTheta(int(line_position)))
print('after angle correction: {:.3}'.format(two_theta))

Output:

Pixel 22 2theta
before angle correction: ...
after angle correction: ...

Categories: AlgorithmIndex | Reflectometry

Source

C++ header: SpecularReflectionPositionCorrect2.h

C++ source: SpecularReflectionPositionCorrect2.cpp