application definition, extends NXobject
Application definition for a generic scan instrument.
This definition is more an example then a stringent definition as the content of a given NeXus scan file needs to differ for different types of scans. This example definition shows a scan like done on a rotation camera: the sample is rotated and a detector image, the rotation angle and a monitor value is stored at each step in the scan. In the following, the symbol
NPis used to represent the number of scan points. These are the rules for storing scan data in NeXus files which are implemented in this example:
Each value varied throughout a scan is stored as an array of length
NPat its respective location within the NeXus hierarchy.
For area detectors,
NPis the first dimension, example for a detector of 256x256:
The NXdata group contains links to all variables varied in the scan and the data. This to give an equivalent to the more familiar classical tabular representation of scans.
These rules exist for a reason: HDF allows the first dimension of a data set to be unlimited. This means the data can be appended too. Thus a NeXus file built according to the rules given above can be used in the following way:
At the start of a scan, write all the static information.
At each scan point, append new data from varied variables and the detector to the file.
The symbol(s) listed here will be used below to coordinate datasets with the same shape.
nP: Number of points
xDim: xDim description
yDim: yDim description
ENTRY: (required) NXentry
title: (required) NX_CHAR
start_time: (required) NX_DATE_TIME
end_time: (required) NX_DATE_TIME
definition: (required) NX_CHAR
Official NeXus NXDL schema to which this file conforms
INSTRUMENT: (required) NXinstrument
SAMPLE: (required) NXsample
rotation_angle: (required) NX_FLOAT (Rank: 1, Dimensions: [nP])
MONITOR: (required) NXmonitor
data: (required) NX_INT (Rank: 1, Dimensions: [nP])
DATA: (required) NXdata
List of hypertext anchors for all groups, fields, attributes, and links defined in this class.