\(\renewcommand\AA{\unicode{x212B}}\)

CreatePoleFigureTableWorkspace v1

Summary

Creates a table storing the pole figure data extracted from the input workspaces.

Properties

Name	Direction	Type	Default	Description
InputWorkspace	Input	MatrixWorkspace	Mandatory	The workspace containing the input data.
PeakParameterWorkspace	Input	TableWorkspace		Optional workspace containing the fitted peak data.
OutputWorkspace	Output	TableWorkspace	Mandatory	Output workspace containing the table of alphas, betas and intensities.
Reflection	Input	dbl list	0,0,0	Reflection number for peak being fit. If given, algorithm will attempt to use the CrystalStructure on the InputWorkspace to adjust intensity for scattering power.
Chi2Threshold	Input	number	2	Minimum chi^2 value to include in table. If set to 0.0, no chi^2 filtering will be performed.
PeakPositionThreshold	Input	number	0.1	Maximum distance of fitted peak X0 from HKL X0 value to include in table.If set to 0.0, no positional filtering will be performed. If no Reflection is specified, this tolerance can be ignored, otherwise it will assume X0 in PeakParameterWorkspace is given in dSpacing.
ApplyScatteringPowerCorrection	Input	boolean	True	Flag for determining whether the provided intensities should be corrected for scattering power
ScatteringVolumePosition	Input	dbl list	0,0,0	Position where the diffraction vectors should be calculated from, defaults as the origin

Description

Create a table with the information required to produce a pole figure, namely, a collection of alphas, betas, and intensities. Here alpha and beta are referring to spherical coordinates in the reference frame of the sample. Alpha is described as the azimuthal angle taken from the x-axis of the sample. Beta is described as the elevation angle from the y-axis of the sample.

If a peak parameters table is provided it is expected that intensities (“I”), chi squared values (“chi2”), and peak positions (“X0”) are all present. The requirement for chi2 and peak positions can be overridden by setting their respective thresholds to 0.0. If no peak parameter table is given, the chi squared will be assumed to be 0, the intensities assumed to be 1, and no peak positions will be considered. It is further expected that the number of rows in this table exactly matches the number of spectra provided.

The algorithm supports selection of which spectra from the input are included in the final table, by use of both a threshold on the peak position and on the chi squared value. If a reflection is specified, the algorithm will check that the fit X0 value in the peak parameter table is within PeakThreshold of the d spacing value for the specified peak (Note: as such, specifying a reflection requires a Crystal Structure concept page be set on the Input Workspace). If no reflection is given, this PeakThreshold will check X0 is within threshold value of the mean X0 value. If a chi squared threshold is specified, only spectra with a fit chi2 value in the peak parameter table lower than the threshold will be included in the output table.

By default, the beam is anticipated to be incident on (0,0,0) for calculation of incident beam diffraction vector and the detector scattering vectors, if this is not the case, set ScatteringVolumePosition to calculate scattering vectors from another position instead.

Note: If a reflection is provided, the intensity is also, by default, normalised by scattering power, as described in ref [1]. This can be prevented by setting, ApplyScatteringPowerCorrection to False

References

[1]

Malamud, F., Santisteban, J. R., Vicente Alvarez, M. A., Bolmaro, R., Kelleher, J., Kabra, S. & Kockelmann, W. (2014). Texture analysis with a time-of-flight neutron strain scanner. J. Appl. Cryst. 47, https://doi.org/10.1107/S1600576714012710

Usage

Create Pole Figure Table Example

# import mantid algorithms, numpy and matplotlib
from mantid.simpleapi import *
import matplotlib.pyplot as plt
import numpy as np
from mantid.geometry import CrystalStructure

# create a workspace
ws = CreateWorkspace(
    DataX=[0., 1.],
    DataY=[1., 2., 3.,4.],
    NSpec=4)


# set the instrument to have a detector at 2theta
EditInstrumentGeometry(Workspace='ws',
                       PrimaryFlightPath = 50, L2=[50,50,50,50], Polar=[85, 90, 95, 90],
                       Azimuthal= [0,0,0,45], DetectorIDs = [0,1,2,3])

# set a crystal structure
xtal = CrystalStructure("5.431 5.431 5.431", "F d -3 m", "Si 0 0 0 1.0 0.05")

# declare a reflection of interest
hkl = "(1,1,1)"

# define a sample shape
sample_shape = f"""
<cylinder id="A">
  <centre-of-bottom-base x="0" y="0" z="0.05" />
  <axis x="0" y="0" z="-1" />
  <radius val="0.1" />
  <height val="0.1" />
</cylinder>
"""

# apply a generic rotation, set the sample and crystal structure
SetGoniometer("ws", Axis0="45,0,1,0,1")
SetSample('ws', Geometry={'Shape': 'CSG', 'Value': sample_shape})
ws.sample().setCrystalStructure(xtal)

# Create an example PeakParameter Table
peak_param_table = CreateEmptyTableWorkspace(OutputWorkspace = "PeakParameterWS")
for col in ("I", "X0", "chi2"):
    peak_param_table.addColumn("double", col)
for i in range(4):
    val = 1.0 + (i / 10)
    peak_param_table.addRow([val, 3.14+(i/100), i]) # 3.14 hkl (1,1,1) dSpacing


# run alg
CreatePoleFigureTableWorkspace(InputWorkspace = "ws",
                                       PeakParameterWorkspace = "PeakParameterWS",
                                       OutputWorkspace = "outWS",
                                       PeakPositionThreshold = 0.0,
                                       Chi2Threshold = 0.0)

Categories: AlgorithmIndex | Diffraction\Engineering

Source

Python: CreatePoleFigureTableWorkspace.py