AlignAndFocusPowderSlim v1¶

Warning

This algorithm is currently for the VULCAN instrument testing purposes

Summary ¶

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

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.
ProcessBankSplitTask	Input	boolean	False	For development testing. Changes how the splitters are processed. If true then use ProcessBankSplitTask otherwise loop over ProcessBankTask.
CorrectionToSample	Input	boolean	False	Find time-of-flight when neutron was at the sample position. This is only necessary for fast logs (i.e. more frequent than proton on target pulse).
UseFullTime	Input	boolean	False	If true, events will be splitting using full time values (tof+pulsetime) rather than just pulsetime.
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.
GroupingWorkspace	Input	GroupingWorkspace		A GroupingWorkspace giving the grouping info. If not provided then the grouping from the calibration file will be used if provided, else a default grouping of one group per bank.
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’]
LogAllowList	Input	str list		If specified, only these logs will be loaded from the file
LogBlockList	Input	str list		If specified, these logs will not be loaded from the file
OutputWorkspace	Output	Workspace	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.
BankNumber	Input	number	Optional	The bank for which to read data; if specified, others will be blank
L1	Input	number	Mandatory	The primary distance \(\ell_1\) from beam to sample
L2	Input	dbl list	Mandatory	The secondary distances \(\ell_2\) from sample to focus group
Polar	Input	dbl list	Mandatory	The effective polar angle (\(2\theta\)) of each focus group
Azimuthal	Input	dbl list		The effective azimuthal angle \(\phi\) for each focus group

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

does not support copping data
does not support removing prompt pulse

Child algorithms used are

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",
                             L1=43.755,
                             L2=[2.296, 2.296, 2.070, 2.070, 2.070, 2.530],
                             Polar=[90, 90, 120, 150, 157, 65.5],
                             Azimuthal=[180, 0, 0, 0, 0, 0])

# 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",
             GroupWorkspaces=True)
out = Rebin("filtered", "0,50000,50000", PreserveEvents=False)

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

Example - splitting 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,
                     LogValueInterval=0.01)

# Use the splitter table to filter the events during loading and output to workspace group
ws = AlignAndFocusPowderSlim("VULCAN_218062.nxs.h5", SplitterWorkspace='splitter',
                             L1=43.755,
                             L2=[2.296, 2.296, 2.070, 2.070, 2.070, 2.530],
                             Polar=[90, 90, 120, 150, 157, 65.5],
                             Azimuthal=[180, 0, 0, 0, 0, 0])
print(ws.getNumberOfEntries())  # should be 6 workspaces in the group

# By default the events are split based on pulsetime of the events. If you want to split based on full time (pulsetime + tof), set UseFullTime=False.
ws2 = AlignAndFocusPowderSlim("VULCAN_218062.nxs.h5",
                              SplitterWorkspace='splitter',
                              UseFullTime=True,
                              L1=43.755,
                              L2=[2.296, 2.296, 2.070, 2.070, 2.070, 2.530],
                              Polar=[90, 90, 120, 150, 157, 65.5],
                              Azimuthal=[180, 0, 0, 0, 0, 0])

Example - filter bad pulses

ws = AlignAndFocusPowderSlim("VULCAN_218062.nxs.h5",
                             XMin=0, XMax=50000, XDelta=50000,
                             BinningMode="Linear",
                             BinningUnits="TOF",
                             FilterBadPulses=True,
                             L1=43.755,
                             L2=[2.296, 2.296, 2.070, 2.070, 2.070, 2.530],
                             Polar=[90, 90, 120, 150, 157, 65.5],
                             Azimuthal=[180, 0, 0, 0, 0, 0])

# 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, CheckSpectraMap=False, CheckInstrument=False)

Example - using a GroupingWorkspace

You can provide a GroupingWorkspace to define how the detectors are grouped in the output workspace. If a GroupingWorkspace is not provided, the grouping from the calibration file will be used if provided, else a default grouping of one group per bank is used.

The example done here is using GenerateGroupingPowder to create a grouping workspace. With an angle step of 45 degrees, this will create 3 groups.

inst = LoadEmptyInstrument(InstrumentName="VULCAN")
GenerateGroupingPowder(inst, GroupingWorkspace='powder_group', AngleStep=45)

ws = AlignAndFocusPowderSlim("VULCAN_218062.nxs.h5", GroupingWorkspace="powder_group",
                             L1=43.755,
                             L2=[2, 2.25, 2.5],
                             Polar=[90]*3)

print(ws.getNumberHistograms())  # should be 3 histograms in the output workspace

Categories: AlgorithmIndex | Workflow\Diffraction

Source ¶

C++ header: AlignAndFocusPowderSlim.h

C++ source: AlignAndFocusPowderSlim.cpp

AlignAndFocusPowderSlim v1¶

Summary ¶

See Also ¶

Properties ¶

Description ¶

Usage ¶

Source ¶

AlignAndFocusPowderSlim v1¶

Summary¶

See Also¶

Properties¶

Description¶

Usage¶

Source¶

Summary ¶

See Also ¶

Properties ¶

Description ¶

Usage ¶

Source ¶