3.2.1.2. NXDL: Data Types and Units¶
Data Types allowed in NXDL specifications¶
Data types for use in NXDL
describe the expected type of data for a NeXus field. These terms are very
broad. More specific terms are used in actual NeXus data files that describe
size and array dimensions. In addition to the types in the following table, the
NAPI type is defined when one wishes to permit a field
with any of these data types.
| ISO8601: | ISO 8601 date and time representation (http://www.w3.org/TR/NOTE-datetime) |
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| NX_BINARY: | any representation of binary data - if text, line terminator is [CR][LF] |
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| NX_BOOLEAN: | true/false value ( true | 1 | false | 0 ) |
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| NX_CHAR: | any string representation |
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| NX_DATE_TIME: | alias of ISO8601 |
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| NX_FLOAT: | any representation of a floating point number |
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| NX_INT: | any representation of an integer number |
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| NX_NUMBER: | any valid NeXus number representation |
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| NX_POSINT: | any representation of a positive integer number (greater than zero) |
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| NX_UINT: | any representation of an unsigned integer number (includes zero) |
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Unit Categories allowed in NXDL specifications¶
Unit categories in NXDL specifications describe the expected type of units for a NeXus field. They should describe valid units consistent with the NeXus units section. The values for unit categories are restricted (by an enumeration) to the following table.
| NX_ANGLE: | example: degrees or radians or arcminutes or |
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| NX_ANY: | usage: things like logs that aren’t picky on units |
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| NX_AREA: | example: m2 or barns |
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| NX_CHARGE: | example: pC or C |
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| NX_CROSS_SECTION: | |
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| example: barns | |
| NX_CURRENT: | example: A |
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| NX_DIMENSIONLESS: | |
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| for fields where the units cancel out, example: “” or mm/mm (NOTE: not the same as NX_UNITLESS) | |
| NX_EMITTANCE: | emittance (length * angle) of a radiation source, example: nm*rad |
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| NX_ENERGY: | example: J or keV |
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| NX_FLUX: | example: s-1 cm-2 |
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| NX_FREQUENCY: | example: Hz |
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| NX_LENGTH: | example: m |
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| NX_MASS: | example: g |
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| NX_MASS_DENSITY: | |
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| example: g cm-3 | |
| NX_MOLECULAR_WEIGHT: | |
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| example: g mol-1 | |
| NX_PERIOD: | (alias to NX_TIME) period of pulsed source, example: microseconds |
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| NX_PER_AREA: | example: cm-2 |
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| NX_PER_LENGTH: | example: cm-1 |
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| NX_POWER: | example: W |
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| NX_PRESSURE: | example: Pa |
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| NX_PULSES: | (alias to NX_NUMBER) clock pulses |
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| NX_SCATTERING_LENGTH_DENSITY: | |
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| example: cm-2 | |
| NX_SOLID_ANGLE: | example: sr | steradian |
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| NX_TEMPERATURE: | example: K |
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| NX_TIME: | example: s |
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| NX_TIME_OF_FLIGHT: | |
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| (alias to NX_TIME) example: s | |
| NX_UNITLESS: | for fields that don’t have a unit (e.g. hkl) so that they don’t inherit the wrong units (NOTE: not the same as NX_DIMENSIONLESS) |
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| NX_VOLTAGE: | example: V |
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| NX_VOLUME: | example: m3 |
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| NX_WAVELENGTH: | example: angstrom |
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| NX_WAVENUMBER: | units for Q, example: angstrom-1 or nm-1 |
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