TabOK

Should the FITS-WCS -TAB algorithm be recognised?

Description:

This attribute is an integer value which indicates if the " -TAB" algorithm, defined in FITS-WCS paper III, should be supported by the FitsChan. The default value is zero. A zero or negative value results in no support for -TAB axes (i.e. axes that have " -TAB" in their CTYPE keyword value). In this case, the astWrite method will return zero if the write operation would required the use of the -TAB algorithm, and the astRead method will return a NULL pointer if any axis in the supplied header uses the -TAB algorithm.

If TabOK is set to a non-zero positive integer, these methods will recognise and convert axes described by the -TAB algorithm, as follows:

The astWrite method will generate headers that use the -TAB algorithm (if possible) if no other known FITS-WCS algorithm can be used to describe the supplied FrameSet (but see the ForceTab attribute). This will result in a table of coordinate values and index vectors being stored in the FitsChan. After the write operation, the calling application should check to see if such a table has been stored in the FitsChan. If so, the table should be retrived from the FitsChan using the astGetTables method, and the data (and headers) within it copied into a new FITS binary table extension. See astGetTables for more information. The FitsChan uses a FitsTable object to store the table data and headers. This FitsTable will contain the required columns and headers as described by FITS-WCS paper III - the coordinates array will be in a column named " COORDS" , and the index vector(s) will be in columns named " INDEX$<$i$>$" (where $<$i$>$ is the index of the corresponding FITS WCS axis). Note, index vectors are only created if required. The EXTNAME value will be set to the value of the AST__TABEXTNAME constant (currently " WCS-TAB" ). The EXTVER header will be set to the positive integer value assigned to the TabOK attribute. No value will be stored for the EXTLEVEL header, and should therefore be considered to default to 1.