NDF2UNF - Converts an NDF to a sequential unformatted file

Description:

This application converts an NDF to a sequential unformatted Fortran file. Only one of the array components may be copied to the output file. Preceding the data there is an optional header consisting of either the FITS extension with the values of certain keywords replaced by information derived from the NDF, or a minimal FITS header also derived from the NDF.

Usage:

ndf2unf in out [comp] [noperec]

Parameters:

COMP = LITERAL (Read)

The NDF component to be copied. It may be "Data", "Quality" or "Variance". ["Data"]

FITS = _LOGICAL (Read)

If TRUE, any FITS extension is written to start of the output file, unless there is no extension whereupon a minimal FITS header is written to the unformatted file. [FALSE]

IN = NDF (Read)

Input NDF data structure. The suggested default is the current NDF if one exists, otherwise it is the current value.

NOPEREC = _INTEGER (Read)

The number of data values per record of the output file. It must be positive. The suggested default is the current value. [The first dimension of the NDF]

OUT = FILENAME (Write)

Name of the output sequential unformatted file. The file will but always fixed-length records when there is no header.

Examples:

ndf2unf cluster cluster.dat

This copies the data array of the NDF called cluster to an unformatted file called cluster.dat. The number of data values per record is equal to the size of the first dimension of the NDF.

ndf2unf cluster cluster.dat v

This copies the variance of the NDF called cluster to an unformatted file called cluster.dat. The number of variance values per record is equal to the size of the first dimension of the NDF.

ndf2unf cluster cluster.dat noperec=12

This copies the data array of the NDF called cluster to an unformatted file called cluster.dat. There are twelve data values per record in cluster.dat.

ndf2unf out=ndf234.dat fits in=@234

This copies the data array of the NDF called 234 to an unformatted file called ndf234.dat. The number of data values per record is equal to the size of the first dimension of the NDF. If there is a FITS extension, it is copied to ndf234.dat with substitution of certain keywords, otherwise a minimal FITS header is produced.

Notes:

The details of the conversion are as follows:

• the NDF array as selected by COMP is written to the unformatted file in records following an optional header.

• HISTORY is not propagated.

• ORIGIN information is lost.

• When a header is to be made, it is composed of FITS-like card images as follows:
  • The number of dimensions of the data array is written to the keyword NAXIS, and the actual dimensions to NAXIS1, NAXIS2 etc. as appropriate.

  • If the NDF contains any linear axis structures the information necessary to generate these structures is written to the FITS-like headers. For example, if a linear AXIS(1) structure exists in the input NDF the value of the first data point is stored with the keyword CRVAL1, and the incremental value between successive axis data is stored in keyword CDELT1. By definition the reference pixel is 1.0 and is stored in keyword CRPIX1. If there is an axis label it is written to keyword CTYPE1, and axis unit is written to CUNIT1. (Similarly for AXIS(2) structures etc.) FITS does not have a standard method of storing axis widths and variances, so these NDF components will not be propagated to the header. Non-linear axis data arrays cannot be represented by CRVALn and CDELTn, and must be ignored.

  • If the input NDF contains TITLE, LABEL or UNITS components these are stored with the keywords TITLE, LABEL or BUNIT respectively.

  • If the input NDF contains a FITS extension, the FITS items may be written to the FITS-like header, with the following exceptions:
    • BITPIX is derived from the type of the NDF data array, and so it is not copied from the NDF FITS extension.
    • NAXIS, and NAXISn are derived from the dimensions of the NDF data array as described above, so these items are not copied from the NDF FITS extension.
    • The TITLE, LABEL, and BUNIT descriptors are only copied if no TITLE, LABEL, and UNITS NDF components respectively have already been copied into these headers.
    • The CDELTn, CRVALn, CTYPEn, CUNITn, and CRTYPEn descriptors in the FITS extension are only copied if the input NDF contained no linear axis structures.
    • The standard order of the FITS keywords is preserved, thus BITPIX, NAXIS and NAXISn appear immediately after the first card image, which should be SIMPLE.
    • BSCALE and BZERO in a FITS extension are copied when BITPIX is positive, i.e. the array is not floating-point.

  • An extra header record with keyword UNSIGNED and logical value T is added when the array data type is one of the HDS unsigned integer types. This is done because standard FITS does not support unsigned integers, and allows (in conjunction with BITPIX) applications reading the unformatted file to determine the data type of the array.

  • The last header record card will be the standard FITS END.

• Other extensions are not propagated.

Related Applications :

CONVERT: UNF2NDF.

Implementation Status:

• The value of bad pixels is not written to a FITS-like header record with keyword BLANK.