root:NXroot
  entry:NXentry
    @default = "preview"
    # thumbnail image (for file icon use) is a NeXus issue
    # https://github.com/nexusformat/definitions/issues/381
    # TODO: preview image of the data
    preview:NXdata
      # TODO: (needs structure of plottable data)
      # points to a subset of the data to make the quick plot
      # Virtual detector
      @axes = ['scan_x', 'scan_y']
      @signal = 'data'
      # TODO this would be vector scan. How to represent axes for raster scan?
      scan_x -> /entry/instrument/scan/x
      scan_y -> /entry/instrument/scan/y
      data -> /entry/instrument/brightfield/data
    data:NXdata
      @axes = ['scan_x', 'scan_y']
      @signal = 'data'
      # TODO this would be vector scan. How to represent axes for raster scan?
      scan_x -> /entry/instrument/scan/x
      scan_y -> /entry/instrument/scan/y
      data -> /entry/instrument/detector/data
    instrument:NXinstrument
      source:NXsource
        type = ["Thermionic", "Schottky Field Emission", "Cold Field Emission"] # Pulsed sources TBD
        probe = "electron"
        voltage = 300
          @units = 'kV'
        # The rest of NXsource is self-explanatory, add later
      probe:NXbeam
        distance = 0 # By the definition of the probe is at the sample position
        
        convergence_angle = NX_FLOAT
          @units = 'mrad'
        spot_size = NX_FLOAT
          @units = 'nm' # To be agreed in the community
        spot_size_indicator = NX_INT # To be worked out, instrument-specific
        defocus = NX_FLOAT
          @units = 'nm'
        flux = NX_FLOAT
          @units = 'pA'
      detector:NXdetector
        beam_center_x = 0
          @units = 'm'
        beam_center_y = 0
          @units = 'm'
        # Add camera_length to NXdetector class definition    
        camera_length = 0.7
          @units = 'm'
        data = float32(256x256x128x128) # Does this mean the dataset itself in the HDF5 file will be 3D? How will this affect chunking? (Dieter) Good question, this is what we have to discuss now!
        layout = 'area'
        x_pixel_size = 0.00015
          @units = 'm'
        y_pixel_size = 0.00015
          @units = 'm'
      # TODO Item
      brightfield:NXdata
        # matching detector layout
        mask = NX_FLOAT[][]
        # matching scan layout
        data = NX_FLOAT[][]
      # Update class definition NXPositioner: Include scan generators for e-beam    
      # for time series data: NXlog
      # http://download.nexusformat.org/doc/html/classes/base_classes/NXlog.html#nxlog
      # Alternatively NXtransformation? How to express scanning with that?
      scan:NXpositioner
        scan_type = ["raster", "vector"]
        
        # For raster
        start_x = NX_FLOAT
        start_y = NX_FLOAT
        step_x = NX_FLOAT
        step_y = NX_FLOAT
        rotation = NX_FLOAT
        
        dwell_time = NX_FLOAT
        
        # For vector
        x = NX_FLOAT[]
        y = NX_FLOAT[]
        
        # Drift correction
        drift_x = NX_FLOAT[] 
        drift_y = NX_FLOAT[] 
        
      # Or NXtransformation as well?  
      stage:NXpositioner
        x = NX_FLOAT[]
        y = NX_FLOAT[]
        z = NX_FLOAT[]
        tilt_alpha = NX_FLOAT[]
        tilt_beta = NX_FLOAT[]
        rotation = NX_FLOAT[]
        drift_x = NX_FLOAT[] 
        drift_y = NX_FLOAT[] 

# Links from Hangout chat:

http://download.nexusformat.org/doc/html/classes/base_classes/NXsource.html#nxsource
http://download.nexusformat.org/doc/html/classes/applications/NXstxm.html#nxstxm
https://github.com/prjemian/spec2nexus/blob/master/src/spec2nexus/eznx.py#L182
http://download.nexusformat.org/doc/html/utilities.html?highlight=validation#validation
http://download.nexusformat.org/doc/html/classes/base_classes/NXpositioner.html#nxpositioner
http://download.nexusformat.org/doc/html/classes/base_classes/NXtransformations.html#nxtransformations
http://download.nexusformat.org/sphinx/classes/base_classes/NXpositioner.html
http://cansas-org.github.io/canSAS2012/examples.html#d-image
Contact at HDF Group regarding chunking: Elena Pourmal <[e-mail]>
http://download.nexusformat.org/doc/html/datarules.html?highlight=unidata#nexus-data-units
thumbnail images are a proposal in NeXus that looks like it is converging to implementation: https://github.com/nexusformat/definitions/issues/381
NeXus conference call (biweekly) https://www.nexusformat.org/Teleconferences.html

# Next steps:

* Send summary to mailing lists for feedback
* Build file following this structure from existing data
* Validate that structure
* Implement in LiberTEM and other SW