NXM Help Data

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Summary: Data structures, formats, and binary representations.

A Data object consists of an array of 1 or more Atoms.

An Atom is an N-dimensional quantity defined by a data mode (Scalar,
Complex, Vector, ...), and a data type (Double, Float, Int, ...).

Foreign data sources also have a data representation (IEEE, VAX, CRAY, ...).

Format - Atomic Formats available as elements

The format of individual data points within a Midas file is specified by a two-character data format digraph. The first character is the data "mode" , indicating how data values are grouped together. Possible data modes are:

S       Scalar
C       Complex
V       Vector (three-elements, e.g. x, y, z coordinates)
Q       Quad (four-elements, e.g. x, y, z, time coordinates)
M       Matrix (three-by-three, e.g. coordinate-transformation)
T       Transformation Matrix (4x4 e.g. coord-trans + scaling)
U       User-defined
1-9     Generic multiplier

The second character of the data format is the actual data type:

P       Packed bit data
O       Offset byte
B       Byte
I       Integer (two bytes)
L       Long integer (four bytes)
F       Floating point
D       Double precision floating point
A       ASCII (eight characters)

This gives a total of 48 standard data formats, such as SF (scalar floating point), CB (complex byte), QD (quad double precision), plus User-defined and Generic. The user-defined type is designated Un, where n is a one-digit number. If n is positive, it is the number of bytes per element, otherwise the number of bits per element. Generic organization is normally used with ASCII format, for example 8A. (NOTE that one ASCII atom in this sense is considered to be eight bytes, so an 8A file consumes 64 bytes per element.) Finally, when Type 3000 or 5000 records are non-homogeneous (mixed data formats within the record), the overall file data format is shown as NH (non-homogeneous).

Representation - underlying binary data formats

The data representations supported are:

VAX   - VAX/VMS
IEEE  - IEEE Big-Endian (e.g. Sun)
EEEI  - IEEE Little-Endian (e.g. IBM PC)

NOTE: With scalar packed (SP) data, NeXtMidas supports IEEE and EEEI. X-Midas did not distinguish between IEEE/EEEI SP data. Consequently, one may have to change the data representation with the use of the HEADERMOD command or qualifiers.

~SeeAlso CONVERT, HEADERMOD, QUALIFIERS