ReflectometryISISCalibration v1#

Summary#

Corrects detector pixel positions using a calibration file and a selected instrument workflow.

Properties#

Name	Direction	Type	Default	Description
InputWorkspace	Input	`Workspace`	Mandatory	An input workspace or workspace group.
CalibrationFile	Input	string		Calibration data file containing detector IDs and offsets for the default workflow, or spectrum numbers and absolute theta values for the POLREF workflow. Allowed values: [‘dat’]
InstrumentWorkflow	Input	string	Default	The instrument workflow that defines how the calibration file should be interpreted. Allowed values: [‘Default’, ‘POLREF’]
SpecularPixelSpectrumNo	Input	number	Optional	The spectrum number of the specular pixel in the subject run. Required for the POLREF workflow.
ExperimentAngle	Input	number	Optional	The experiment theta angle in degrees. Required for the POLREF workflow.
OutputWorkspace	Output	`Workspace`	Mandatory	The calibrated output workspace.

ReflectometryISISCalibration#

This algorithm adjusts the positions of individual detector pixels in a workspace based on the calibration values provided in the calibration file. The algorithm takes a copy of the input workspace before applying the position changes, so the original workspace remains unchanged.

A .dat calibration file must be provided via the CalibrationFile property. Lines beginning with # are ignored.

The InstrumentWorkflow property controls the meaning of the calibration values:

Default: the file should contain two, space-delimited columns labelled detectorid and theta_offset (the labels are not case-sensitive). The detector IDs are the IDs for the detector pixels that should be moved. The theta offsets are the change required to the two theta value for each detector, in degrees.
POLREF: the file should contain two, space-delimited columns labelled spectrumnumber and angle (the labels are not case-sensitive). The spectrum number is matched against the spectrum number of each non-monitor detector spectrum in the input workspace. The angles are absolute detector theta values in degrees and are converted to two theta offsets internally.

For the POLREF workflow, ExperimentAngle is the experiment theta angle in degrees, and SpecularPixelSpectrumNo is the fitted specular pixel spectrum number for the experiment. The same SpecularPixelSpectrumNo is used in the calibration-file spectrum-number coordinate system and in the input workspace spectrum-number coordinate system. It may be fractional, in which case linear interpolation is used on the calibration file.

The selected InstrumentWorkflow controls how detector positions are corrected. The Default workflow applies detector corrections as vertical shifts. The POLREF workflow rotates detectors around the sample.

The POLREF calibration map has an inverted angular coordinate relative to Mantid’s signed two theta coordinate for the workspace: in current POLREF maps, the calibration-file angle decreases as spectrum number increases, while the workspace signed two theta increases.

The below is an example of a valid calibration file:

# Optional header that can be used
# to include any useful information
detectorid theta_offset
1 -0.05
2 -0.043
3 0.02

For each detector pixel in the calibration file, the algorithm finds the existing two theta value in degrees and then adds the theta offset to calculate the new two theta value (so new two theta = existing two theta + theta offset). This new two theta is then passed to SpecularReflectionPositionCorrect v2, which converts it to cartesian co-ordinates and moves the detector pixel to the new location.

Only the detectors specified in the file will be moved, all other detectors in the workspace will remain in their original positions.

The below is an example of a valid POLREF calibration file:

spectrumnumber angle
3.074720743
3.069434420
3.063999483

For POLREF input, all non-monitor detector spectra in the input workspace are considered. Only spectrum numbers covered by the calibration file range are moved; monitors and spectrum numbers outside the calibration range are left unchanged. Spectrum numbers in the calibration file must be integer. Missing spectrum numbers inside the calibration range, for example dead pixels, are supported by linear interpolation between the neighbouring spectrum-number rows. Fractional specular pixel spectrum numbers are also supported by the same interpolation.

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: Run calibration on a workspace

import os
import numpy as np

# Load an empty workspace
ws = LoadEmptyInstrument(InstrumentName='D17')
detector_info = ws.detectorInfo()
print(f"Before calibration:")
for i in range(1,4):
    two_theta = np.rad2deg(detector_info.twoTheta(detector_info.indexOf(i)))
    print(f"Detector ID {i} two theta: {two_theta}")

# Create a calibration file to change the first 3 detectors
file_name = os.path.join(config["defaultsave.directory"], "TestReflectometryISISCalibration.dat")
f = open(file_name,'w');
f.write('DetectorID Theta_Offset\n')
for i in range(1,4):
   f.write(f'{i} 0.1\n')
f.close();

# Run calibration
calibrated_ws = ReflectometryISISCalibration(InputWorkspace=ws, CalibrationFile=file_name)
detector_info = calibrated_ws.detectorInfo()
print(f"After calibration:")
for i in range(1,4):
    two_theta = np.rad2deg(detector_info.twoTheta(detector_info.indexOf(i)))
    print(f"Detector ID {i} two theta: {two_theta}")

Output:

Before calibration:
Detector ID 1 two theta: 2.791743331094234
Detector ID 2 two theta: 2.7697087152076083
Detector ID 3 two theta: 2.7476732793761274
After calibration:
Detector ID 1 two theta: 2.891743331094271
Detector ID 2 two theta: 2.869708715207532
Detector ID 3 two theta: 2.847673279376101

Source#

Python: ReflectometryISISCalibration.py

ReflectometryISISCalibration v1#

Summary#

See Also#

Properties#

ReflectometryISISCalibration#

Usage#

Source#