General Utilities

STSDAS Tables: the ttools Package

In addition to the image
data format used for all HST data sets, STSDAS (through the TABLES package) supports a table format to handle tabulated information of different data types. It is also used to accommodate output from various analysis tasks and to facilitate communication between packages. STSDAS tables are binary files with data stored in rows and columns. Each table has a set of columns, containing various data types (i.e., character, integer, floating point, and boolean). All data values in a particular column must have the same data type. Virtually any number of rows can be in a table, and there is no restriction that the columns must fit across a terminal screen. Thus, it is possible to have a table with hundreds of columns.

Each column has the following attributes:

Header parameters may also have data types of real, double, integer, boolean, or text. Header keywords are limited to eight characters (for FITS compatibility) and are converted to upper case.

Data in STSDAS tables are accessed using the name of the column. There is no need for the user to know the position of a column within a table, and the column names can be easily viewed using tasks in the ttools package. Because table entries are accessed by column name, information in a table can be easily shared by different applications: users (or programmers) need only know the name of the column containing the appropriate information.

Each STSDAS table is stored in a single file. By default, tables have the filename extension .tab. While you may give tables any filename and extension, it will be most convenient to use the default .tab extension, otherwise you will have to specify the extension explicitly when using the various table manipulation tools. Unless a table is opened read/write, STDIN and STDOUT are acceptable names for input and output text tables.

The table I/O software can also read and write plain ASCII tables. These are simply text files in row and column format. Column names in text tables are accessed by column number but using a character string starting with "c" and followed by the column number: c1, c2, c3, etc. While the file name of a binary table must have an extension, the name of a text table need not.

Users will find many opportunities for using STSDAS tables. Each calibration pipeline task (calxxx) reads from STSDAS tables to get the necessary calibration constants. The IRAF daophot package can produce results in either IRAF internal data base format or STSDAS table format. Tables produced by tasks such as daophot can then be analyzed using facilities in the ttools package.

The ttools Package

The ttools package contains a rich set of tasks for inspecting, editing (both with a text editor and with a graphic-based editor), and processing the information in tables. These tasks can be grouped as follows:

Several other tasks can be found in the ttools package but are not described here. These include: tcheck, tdump, tmerge, imtab, and tabim.

The ttools Package

Generated with WebMaker