6.2

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SaveGEMMAUDParamFile v1

../_images/SaveGEMMAUDParamFile-v1_dlg.png

SaveGEMMAUDParamFile dialog.

Summary

Read calibration information from focused workspace and GSAS parameter file, and save to MAUD-readable calibration format

Properties

Name Direction Type Default Description
InputWorkspace Input WorkspaceGroup Mandatory WorkspaceGroup of focused banks
GSASParamFile Input string Mandatory GSAS parameter file to read diffractometer constants and profile coefficients from
TemplateFilename Input string /jenkins_workdir/workspace/release_clean-ubuntu-18.04/scripts/Diffraction/isis_powder/gem_routines/maud_param_template.maud Template for the .maud file
GroupingScheme Input long list   An array of bank IDs, where the value at element i is the ID of the bank in GSASParamFile to associate spectrum i with
OutputFilename Input string Mandatory Name of the file to save to

Description

Creates a .maud calibration file from a set of focused diffraction workspaces and a GSAS calibration file.

MAUD Format

.maud is a text-based format used to convert the data in a GDA file (see SaveGDA) from TOF to D-spacing in MAUD. The algorithm uses a template to produce its output, which lives in scripts/Diffraction/isis_powder/gem_routines/maud_param_template.maud.

The parameters of interest in the .maud file are:

  • Bank IDs - essentially just a label for each spectrum in MAUD
  • Diffractometer constants (also called conversion factors, or sometimes DIFC values) DIFC, DIFA and TZERO. These are explained in section 1 of Refinement of time of flight Profile Parameters in GSAS [RonSmith]
  • Scattering angles for each bank, theta and eta (more normally called phi
  • Profile coefficients for GEM’s chosen peak shape (GSAS TOF function type 1) alpha-0, alpha-1, beta-0, beta-1, sigma-0, sigma-1 and sigma-2. These are explained on page 143 of the GSAS Manual [GSASManual]
  • Sample-detector distance
  • There are also parameters for a second function, GSAS TOF function type 2, which are zeroed

Bank Grouping

It should be noted that calibration parameters are not given for every bank, as generating such a file would be impractical, given the data we get from texture experiments on GEM.

Instead we assign each of the 160 banks the parameters from one of the 6 banks used when focusing GEM data normally. This algorithm’s ‘sister algorithm’, SaveGDA applies a D to TOF conversion using the same parameters per bank (essentially faking the time-of-flight). See D to TOF Conversion for more details on this.

References:

[RonSmith]Smith, R. “Refinement of time of flight Profile Parameters in GSAS”
[GSASManual]Larson, A. C. & Von Dreele, R. B (2004). “General Structure Analysis System (GSAS)”, Los Alamos National Laboratory Report LAUR 86-748

Usage

import os

def collect_parameter(param_header, file_contents):
    file_index = file_contents.index(param_header) + 1
    param_values = []

    while file_contents[file_index]:
        param_values.append(float(file_contents[file_index]))
        file_index += 1

    return param_values

# Banks 1 to 4 of a previous texture focus in isis_powder
# We don't use the full 160 banks as the test becomes too slow
input_group = Load(Filename="GEM61785_D_texture_banks_1_to_4.nxs",
                   OutputWorkspace="SaveGEMMAUDParamFiletest_GEM61785")

output_file = os.path.join(config["defaultsave.directory"], "GEM61785.maud")
SaveGEMMAUDParamFile(InputWorkspace=input_group,
                     OutputFilename=output_file,
                     GSASParamFile="GEM_PF1_PROFILE.IPF",
                     # Assign spectra 1, 2 and 3 to bank 2 in calib file,
                     # and spectrum 4 to bank 3
                     GroupingScheme=[2, 2, 2, 3])

with open(output_file) as f:
    file_contents = f.read().split("\n")

difcs = collect_parameter("_instrument_bank_difc", file_contents)
print("DIFC values: " + " ".join("{:.2f}".format(difc) for difc in difcs))

thetas = collect_parameter("_instrument_bank_tof_theta", file_contents)
print("Theta values: " + " ".join("{:.2f}".format(theta) for theta in thetas))

Output:

DIFC values: 1468.19 1468.19 1468.19 2788.34
Theta values: 9.12 8.16 8.04 9.06

Categories: AlgorithmIndex | DataHandling\Text | Diffraction\DataHandling