TST

File types: .TAB .tab

Mixed capitalisations, such as .Tab, are also supported.

CURSA can read and write catalogues in the TST (Tab-Separated Table) format. The TST format is a standard for exchanging catalogue data and is commonly used to transfer subsets extracted from remote catalogues or archives across the Internet. Typically when a client such as catremote (see Section ) running on your local computer queries a remote catalogue or archive the selected objects will be returned as a tab-separated table. In addition to CURSA, the TST format is also used by GAIA (see SUN/214[12]), SkyCat and Starbase (see Section ). It is documented in SSN/75[9].

Compared to the other formats supported by CURSA, the TST format is somewhat deficient in the amount of metadata that it includes. In particular, the details stored for each column do not include its data type or units. Consequently, CURSA deduces a data type for each column by reading the values that it contains. This procedure usually works reasonably well, though occasionally it produces bizarre results. Unfortunately there is no similar simple trick which can replace the missing units. If you find that you need to fix-up the column details in a TST catalogue one approach is to use catcopy (see Section ) to convert the catalogue to the STL format (see Appendices  and ) and then edit the STL column definitions, as appropriate. When CURSA writes a TST catalogue it saves the column data type, external format and units. These details are written in a format which CURSA can interpret if it subsequently reads the catalogue. Though this enhancement is specific to CURSA it is entirely consistent with the TST format and does not affect the ability of external programs to read the catalogues. The format in which the additional information is stored is documented in SSN/75.

The TST format does not support vector columns. If a catalogue containing vector columns is written as a tab-separated table each vector element is written as a scalar column.

Unsurprisingly, given its provenance as a medium for transporting subsets extracted from remote catalogues across the Internet, the tab-separated table format is intended for use with relatively small catalogues and is unsuitable for very large ones. Currently CURSA sets no upper limit to the size of catalogue for which it can be used. However, if you attempt to read a catalogue containing more than 15,000 rows a warning message is issued. A large TST format catalogue may take a while to open for reading and CURSA may be unable to access a very large TST catalogue¹⁹.