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AlignAndFocusPowderSlim v1

Warning

This algorithm is currently for the VULCAN instrument testing purposes

Summary

VULCAN ONLY Algorithm to focus powder diffraction data into a number of histograms according to a grouping scheme defined in a CalFile.

See Also

AlignAndFocusPowderFromFiles

Properties

Name	Direction	Type	Default	Description
Filename	Input	string	Mandatory	The name of the Event NeXus file to read, including its full or relative path. The file name is typically of the form INST_####_event.nxs. Allowed extensions: [‘.nxs.h5’, ‘.nxs’, ‘_event.nxs’]
FilterByTimeStart	Input	number	Optional	To only include events after the provided start time, in seconds (relative to the start of the run).
FilterByTimeStop	Input	number	Optional	To only include events before the provided stop time, in seconds (relative to the start of the run).
SplitterWorkspace	Input	Workspace		Input workspace specifying “splitters”, i.e. time intervals and targets for event filtering. Currently only a single output workspace is supported.
RelativeTime	Input	boolean	False	Flag indicating whether in SplitterWorkspace the times are absolute or relative. If true, they are relative to the run start time.
SplitterTarget	Input	number	0	The target workspace index for the splitter.
FilterBadPulses	Input	boolean	False	Filter bad pulses in the same way that FilterBadPulses v1 does.
BadPulsesLowerCutoff	Input	number	95	The percentage of the average to use as the lower bound when filtering bad pulses.
CalFileName	Input	string		The .cal file containing the position correction factors. Either this or OffsetsWorkspace needs to be specified. Allowed extensions: [‘.h5’, ‘.hd5’, ‘.hdf’, ‘.cal’]
XMin	Input	dbl list	0.1	Minimum x-value for the output binning
XDelta	Input	dbl list	0.0016	Bin size for output data
XMax	Input	dbl list	2	Minimum x-value for the output binning
BinningUnits	Input	string	dSpacing	The units of the input X min, max and delta values. Output will always be TOF. Allowed values: [‘dSpacing’, ‘TOF’, ‘MomentumTransfer’]
BinningMode	Input	string	Logarithmic	Specify binning behavior (‘Logarithmic’). Allowed values: [‘Logarithmic’, ‘Linear’]
OutputWorkspace	Output	MatrixWorkspace	Mandatory	An output workspace.
ReadSizeFromDisk	Input	number	100000000	Number of elements of time-of-flight or detector-id to read at a time. This is a maximum
EventsPerThread	Input	number	1000000	Number of events to read in a single thread. Higher means less threads are created.

Description

This is a simplified version of AlignAndFocusPowderFromFiles v1 which uses very few child algorithms. The main feature is that this reads the events, filters and adjusts their time-of-flight, then increments the correct bin in the output workspace. As a result, there is a significantly smaller memory usage and the processing is significantly faster.

Current limitations compared to AlignAndFocusPowderFromFiles

• only supports the VULCAN instrument

• hard coded for 6 particular groups

• does not support copping data

• does not support removing prompt pulse

Child algorithms used are

• LoadDiffCal v1

• LoadIDFFromNexus v1

• EditInstrumentGeometry v1

• LoadNexusLogs v1

• ConvertUnits v1

Usage

Example - event filtering

This algorithm accepts the same SplitterWorkspace inputs as FilterEvents and more information can be found on the Event Filtering page.

# create splitter table using relative time
splitter = CreateEmptyTableWorkspace()
splitter.addColumn('float', 'start')
splitter.addColumn('float', 'stop')
splitter.addColumn('str', 'target')

splitter.addRow((10,20, '0'))
splitter.addRow((200,210, '0'))
splitter.addRow((400,410, '0'))

# pass the splitter table to AlignAndFocusPowderSlim
ws = AlignAndFocusPowderSlim("VULCAN_218062.nxs.h5",
                             SplitterWorkspace=splitter, RelativeTime=True,
                             XMin=0, XMax=50000, XDelta=50000,
                             BinningMode="Linear",
                             BinningUnits="TOF")

# This is equivalent to using FilterEvents with the same splitter table.
# But note that this example doesn't align the data so put everything in 1 big bin to compare.
ws2 = LoadEventNexus("VULCAN_218062.nxs.h5", NumberOfBins=1)
grp = CreateGroupingWorkspace(ws2, GroupDetectorsBy='bank')
ws2 = GroupDetectors(ws2, CopyGroupingFromWorkspace="grp")

FilterEvents(ws2,
             SplitterWorkspace=splitter, RelativeTime=True,
             FilterByPulseTime=True,
             OutputWorkspaceBaseName="filtered")
out = Rebin("filtered_0", "0,50000,50000", PreserveEvents=False)

CompareWorkspaces(ws, out, CheckUncertainty=False, CheckSpectraMap=False, CheckInstrument=False)

Example - filter events based on log values

# Load only the log we need
cave_temperature = LoadEventNexus("VULCAN_218062.nxs.h5",
                                  MetaDataOnly=True,
                                  AllowList="CaveTemperature")

# Use GenerateEventsFilter to create a splitter table based on the log values
GenerateEventsFilter(cave_temperature,
                     OutputWorkspace='splitter',
                     InformationWorkspace='info',
                     LogName='CaveTemperature',
                     MinimumLogValue=70.10,
                     MaximumLogValue=70.15)

# Use the splitter table to filter the events during loading
ws = AlignAndFocusPowderSlim("VULCAN_218062.nxs.h5", SplitterWorkspace='splitter')

Example - filter bad pulses

ws = AlignAndFocusPowderSlim("VULCAN_218062.nxs.h5",
                             XMin=0, XMax=50000, XDelta=50000,
                             BinningMode="Linear",
                             BinningUnits="TOF",
                             FilterBadPulses=True)

# This is equivalent to using FilterBadPulses.
# But note that this example doesn't align the data so put everything in 1 big bin to compare.
ws2 = LoadEventNexus("VULCAN_218062.nxs.h5")
grp = CreateGroupingWorkspace(ws2, GroupDetectorsBy='bank')
ws2 = GroupDetectors(ws2, CopyGroupingFromWorkspace="grp")
ws2 = FilterBadPulses(ws2)
ws2 = Rebin(ws2, "0,50000,50000", PreserveEvents=False)

CompareWorkspaces(ws, ws2, CheckUncertainty=False, CheckSpectraMap=False, CheckInstrument=False)

Note

While we currently only support a single output workspace when filtering events from a splitter table but the output target can be selected with the SplitterTarget property and you can run the algorithm multiple times with different targets. We also can currently only filter based on the pulse time, not the event time-of-flight.

Categories: AlgorithmIndex | Workflow\Diffraction

Source

C++ header: AlignAndFocusPowderSlim.h

C++ source: AlignAndFocusPowderSlim.cpp