NeXus

NeXus is developed as an international standard by scientists and programmers representing major scientific facilities in Europe, Asia, Australia, and North America in order to facilitate greater cooperation in the analysis and visualization of neutron, x-ray, and muon data.

© 2024 NIAC

NIACClasses

NIAC Decisions on NeXus Classes

This section records NIAC decisions on NeXus base classes and application definitions.

NIAC 2003: Instrument definitions and base classes will be fully self describing

NIAC 2003: Instrument definitions and base classes to go into CVS

NIAC 2003: analysis item in NXentry to be replaced with definition

NIAC 2003: NXroot will be defined as

<NXroot file_name="{File name of original NeXus file}"
     file_time="{Date and time of file creation}"
     file_update_time="{Date and time of last file change at
     close}"
     NeXus_version="{Version of NeXus API used in writing the
     file}"
     HDF_version="?"
     HDF5_version="?"
     creator="{facility or program where file originated}?">
     <NXentry name="{entry name}">+</NXentry>
</NXroot>

NIAC 2003: base classes and instrument definitions will not define bit length for primitives. This means that NX_UINT, NX_INT or NX_FLOAT are all that are allowed for numerical items.

NIAC 2003: The template for NXentry is

<NXentry name="{Entry Name}">
     <title>{Extended title for entry}</title>
     <definition version="{DTD version number}" URL="{URL of DTD
        file}">{Name of entry DTD}</definition>
      <start_time type="ISO8601">{Starting time of
        measurement}</start_time>
     <end_time type="ISO8601">{Ending time of
        measurement}</end_time>
     <duration type="NX_INT" units="seconds">{Duration of
        measurement}</duration>
     <experiment_identifier
        type="NX_CHAR[]">{}</experiment_identifier>
     <run_number type="NX_INT">{Number of run or scan stored in
        this entry}</run_number>
     <run_cycle type="NX_CHAR[]">{}</run_cycle>
     <program_name version="{Program version number}">{Name of
        program used to generate this file}</program_name>
     <command_line>{Name of command line used to generate this
        file}</command_line>
     <notes>{Notes describing entry}</notes>
     <NXuser name="{user}"></NXuser>
     <NXsample name="{sample}"></NXsample>
     <NXinstrument name="{Name of instrument}"></NXinstrument>
     <NXmonitor name="{Name of monitor}"></NXmonitor>
     <NXdata name="{Name of data block}"></NXdata>
</NXentry>

NIAC 2003: NXinstrument template consists of at least the following groups

<NXinstrument> 
     <name short_name=”{abbreviated name of instrument}”>{name of instrument}</name> 
     <NXsource/> 
      <NXcrystal/> 
      <NXdisk_chopper/>
      <NXfermi_chopper/>
       <NXvelocity_selector/> 
       <NXguide/> 
       <NXcollimator/>
       <NXaperture/>
       <NXfilter/>
       <NXattenuator/>
       <NXpolarizer/>
        <NXflipper/>
        <NXmirror/>
        <NXdetector/> 
        <NXbeam_stop/> 
</NXinstrument>

NIAC 2003: Each NXlog will contain information for one variable The definition of a NXlog is

<NXlog name=”{identifier for the log}”> 
        <description>{longer description of what is logged}</description>
        <time start=”{written in ISO8601}” units=””  type=”NX_FLOAT”>{time axis for logged quantity}
        </time> 
       <value units=”{units of logged value}”  type=”NX_FLOAT|NX_INT”>{array of logged value, such as temperature}</value> 
       <raw_value units=”{units of raw values}”
            type=”NX_FLOAT|NX_INT”>{array of raw information, such as voltage on a thermocouple}?</raw_value> 
</NXlog>

NIAC 2004: NXcharacterisations is removed from NXentry

NIAC 2004: End-of-line in NXnote is cr

NIAC 2005: describe links as NAPIlink in metaDTD

NIAC 2005: Allow ? and * in definitions to denote groups and fields that are desirable but not necessary.

NIAC 2006: TOF Raw definition ratified

NIAC 2006: Add synchrotron changes to NXsource

NIAC 2006: Add NXinsertion_device

NIAC 2006: Add NXbending_magnet

NIAC 2007: NXmonopowder ratified

NIAC 2007: NXpositioner ratified

NIAC 2007: NXmonitor ratified

NIAC 2007: All classes ratified will be NeXus 2.0.

NIAC 2007HMI: ratified NXcone definition (check where this one is)

NIAC 2007HMI: replace run_number with entry_identifier in NXentry

NIAC 2007HMI: ratified NXarchive

NIAC 2007HMI: ratified NXdetector extensions for CCD cameras: 1. extend type to include: ccd,pixel,image_plate, cmos 2. add field data_file 3. add field flood 4. add field flood_file 5. add field dark 6. add file dark_file 7. add field spatial_distortion 8. add field spatial_distortion_file

NIAC 2010: NXcollection ratified

NIAC 2010: tags scalar, image for datasets

NIAC 2010: muon application definition ratified with some changes

NIAC 2012: NXcharacterisation deprecated

NIAC 2012: add some DECTRICS required fields to NXdetector

NIAC 2014: NXmx, NXtransformations and variants ratified

NIAC 2014: Ratified NXarpes, NXCite with addition of URL, NXfresnel_zone_plate

NIAC 2014: Add a default attribute at root and NXentry level to help in finding default data to plot

NIAC 2014: added decimated as a possible enum to acquisition_mode in NXdetector

NIAC 2014: additional field nominal added to NXmonitor to keep the nominal flux

NIAC 2014: “rgbimage”, “rgbaimage”, “hslimage”, “hslaimage”, “cmykimage” to be added to the interpretation attribute of datasets to encode 3d datasets with colour as added dimension to the 2d image.