***** File TABLFORM.TXT
Table Data Descriptions
The International Halley Watch agreed early on in the project that
all data would be submitted from the individual disciplines to the Lead
Center using the FITS format. When the decision was made to distribute
this information on CD-ROM, it was determined that the data had to have
even broader accessibility. For this reason, the original FITS files,
with contiguous headers and data, were split into separate files. The
original FITS byte stream could then be recovered by concatenating the
appropriate header and data files. PDS labels were constructed to allow
definition of the data files for the Planetary Data System. For each
data there must a FITS header file associated with it.
The convention for naming files on the CD-ROM was proposed by the
IHW Lead Center to include a unique data qualifier for the data. A
specific set of rules was established to identify the net and subnet for
each discipline (given by a letter code). A CD-ROM running number relates
the information contained in the various indices to the files containing
the actual data. A short list of this convention for tables follows:
PDS Object FITS Discipline Letter File Ext
(description) NAXIS = Code
table (filter) 0,2 IR Studies IRFT .tab
table(photometry) 0,2 IR " IRPH .tab
table(polarimetry) 0,2 IR " IRPOL .tab
table (broad band) 0,2 Photometry Polar PMAG .tab
table (narrow band) 0,2 " PFLX .tab
table (polarization) 0,2 " PPOL .tab
table (magnitude) 0,2 Amateur AMV .tab
The file extensions follow suggestions by the Planetary Data System
(SPIDS v1.1) for tabular and image data. In addition, for IHW FITS, the
original headers and data were split into separate files, with filename
extensions as listed below.
.TAB - table data records as ASCII
These PDS labels are metadata (as headers describing data submitted to
the archive). There has been no effort to duplicate the documentation
contained in the full FITS headers because the PDS and FITS headers for
a given data file differ only in the filename extension. Instead we
have attempted to use the power of the PDS label syntax to fully
describe the data structures and thus gain access to software by that group.
Standards for the Preparation and Interchange of Data Sets, Martin, T.
Z., et al, Document D-4683, Jet Propulsion Laboratory, California
Institute of Technology, Pasadena, CA document version 1.1 was the
primary reference to the Object Description Language (ODL) necessary to
create the PDS labels. (We thankfully acknowledge the help of M. Martin,
JPL, for assisting the IHW through version 1.1 of the ODL that allows
for SPECTRUM.) The basic PDS descriptors such as SFDU_LABEL, RECORD_TYPE,
RECORD_BYTES, and FILE_RECORDS are explained in the SPIDS document. The
RECORD_TYPE for all data files is FIXED_LENGTH. The PDS labels have
been formed as fixed length (78 byte) with an embedded CR and LF.
In creating the TABLE descriptions we have found a good correspondence
between the FITS and PDS syntax. For tables, the value of NAXIS2= ROWS,
TFIELDS=COLUMNS, and NAXIS1=ROW_BYTES; in both cases, the default FORMAT
is ASCII. We choose not to describe the values in each column as this
is done fully in the FITS header file and the data itself follows the FITS
record format, i.e., ASCII characters with no delimiters and padded to
multiples of 2880 bytes. The FITS data structure are currently supported
by public domain software that will be distributed with the Archive. The
various content of the table data is always ASCII with no CR or LF and can
parsed separately by using the column description in the .HDR or .LBL files.