ASCII2NDF

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ASCII2NDF

Converts a text file to an NDF

Description:

This application converts a text file to an NDF. Only one of the array components may be created from the input file. Preceding the input data there may be an optional header. This header may be skipped, or may consist of a simple FITS header. In the former case the shape of the NDF has be to be supplied.

Usage:

ascii2ndf in out [comp] [skip] shape [type]

Parameters:

COMP = LITERAL (Read)

The NDF component to be copied. It may be "Data", "Quality" or "Variance". To create a variance or quality array the NDF must already exist. ["Data"]

FITS = _LOGICAL (Read)

If TRUE, the initial records of the formatted file are interpreted as a FITS header (with one card image per record) from which the shape, data type, and axis centres are derived. The last record of the FITS-like header must be terminated by an END keyword; subsequent records in the input file are treated as an array component given by COMP. [FALSE]

IN = FILENAME (Read)

Name of the input text Fortran file. The file will normally have variable-length records when there is a header, but always fixed-length records when there is no header. The maximum record length allowed is 512 bytes.

MAXLEN = INTEGER (Read)

The maximum record length in bytes of records within the input text file. Unless the records are longer than 512 bytes, you can use the default value. The suggested value is the current value. [512]

OUT = NDF (Read and Write)

Output NDF data structure. When COMP is not "Data" the NDF is modified rather than a new NDF created. It becomes the new current NDF.

SHAPE = _INTEGER (Read)

The shape of the NDF to be created. For example, [40,30,20] would create 40 columns by 30 lines by 10 bands. It is only accessed when FITS is FALSE.

SKIP = INTEGER (Read)

The number of header records to be skipped at the start of the input file before finding the data array or FITS-like header. [0]

TYPE = LITERAL (Read)

The data type of the output NDF. It must be one of the following HDS types: "_BYTE", "_WORD", "_REAL", "_INTEGER", "_INT64", "_DOUBLE", "_UBYTE", "_UWORD" corresponding to signed byte, signed word, real, integer, 64-bit integer, double precision, unsigned byte, and unsigned word. See SUN/92 for further details. An unambiguous abbreviation may be given. TYPE is ignored when COMP = "Quality" since the QUALITY component must comprise unsigned bytes (equivalent to TYPE = "_UBYTE") to be a valid NDF. The suggested default is the current value. TYPE is only accessed when FITS is FALSE. ["_REAL"]

Examples:

ascii2ndf ngc253.dat ngc253 shape=[100,60]

This copies a data array from the text file ngc253.dat to the NDF called ngc253. The input file does not contain a header section. The NDF is two-dimensional: 100 elements in x by 60 in y. Its data array has type _REAL.

ascii2ndf ngc253q.dat ngc253 q shape=[100,60]

This copies a quality array from the text file ngc253q.dat to an existing NDF called ngc253 (such as created in the first example). The input file does not contain a header section. The NDF is two-dimensional: 100 elements in x by 60 in y. Its data array has type _UBYTE.

ascii2ndf ngc253.dat ngc253 fits

This copies a data array from the text file ngc253.dat to the NDF called ngc253. The input file contains a FITS-like header section, which is copied to the FITS extension of the NDF. The shape of the NDF is controlled by the mandatory FITS keywords NAXIS, AXIS1, …, AXISn, and the data type by keywords BITPIX and UNSIGNED.

ascii2ndf type="_uword" in=ngc253.dat out=ngc253 maxlen=4000

∖

This copies a data array from the text file ngc253.dat to the NDF called ngc253. The input file does not contain a header section. The NDF has the current shape and data type is unsigned word. The maximum record length is 4000 bytes.

ascii2ndf spectrum ZZ skip=2 shape=200

This copies a data array from the text file spectrum to the NDF called ZZ. The input file contains two header records that are ignored. The NDF is one-dimensional comprising 200 elements of type _REAL.

ascii2ndf spectrum.lis ZZ skip=1 fits

This copies a data array from the text file spectrum.lis to the NDF called ZZ. The input file contains one header record, that is ignored, followed by a FITS-like header section, which is copied to the FITS extension of the NDF. The shape of the NDF is controlled by the mandatory FITS keywords NAXIS, AXIS1, …, AXISn, and the data type by keywords BITPIX and UNSIGNED.

Notes:

The details of the conversion are as follows:

the ASCII-file array is written to the NDF array as selected by COMP. When the NDF is being modified, the shape of the new component must match that of the NDF.
If the input file contains a FITS-like header, and a new NDF is created, i.e. COMP = "Data", the header records are placed within the NDF’s FITS extension. This enables more than one array (input file) to be used to form an NDF. Note that the data array must be created first to make a valid NDF, and it’s the FITS structure associated with that array that is wanted. Indeed the application prevents you from doing otherwise.
The FITS-like header defines the properties of the NDF as follows:
- BITPIX defines the data type: 8 gives _BYTE, 16 produces _WORD, 32 makes _INTEGER, 64 creates _INT64, $-$ 32 gives _REAL, and $-$ 64 generates _DOUBLE. For the first two, if there is an extra header record with the keyword UNSIGNED and logical value T, these types become _UBYTE and _UWORD respectively. UNSIGNED is non-standard, since unsigned integers would not follow in a proper FITS file. However, here it is useful to enable unsigned types to be input into an NDF. UNSIGNED may be created by this application’s sister, NDF2ASCII. BITPIX is ignored for QUALITY data; type _UBYTE is used.
- NAXIS, and NAXISn define the shape of the NDF.
- The TITLE, LABEL, and BUNIT are copied to the NDF TITLE, LABEL, and UNITS NDF components respectively.
- The CDELTn, CRVALn, CTYPEn, and CUNITn keywords make linear axis structures within the NDF. CUNITn define the axis units, and the axis labels are assigned to CTYPEn. If some are missing, pixel co-ordinates are used for those axes.
- BSCALE and BZERO in a FITS extension are ignored.
- BLANK is not used to indicate which input array values should be assigned to a standard bad value.
- END indicates the last header record unless it terminates a dummy header, and the actual data is in an extension.
Other data item such as HISTORY, data ORIGIN, and axis widths are not supported, because the text file has a simple structure to enable a diverse set of input files to be converted to NDFs, and to limitations of the standard FITS header.

Related Applications

Convert: NDF2ASCII; Kappa: TRANDAT; Figaro: ASCIN and ASCOUT.

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