Processing Groups of Data Files

When a KAPPA application requests an input or output data file (either an NDF or a positions list), you may optionally give a group of several data files rather than just one. In this case, the application is automatically re-run until all the supplied data files have been processed. For instance, in the following command:

    % display in="../a*" mode=perc accept

a group of NDFs (all those beginning with ``a'' in the parent directory) are assigned to the IN parameter, and the DISPLAY command is automatically re-run to display each NDF in the fashion of a (rather slow!) movie.

Another example:

    % stats ndf=^files

will display the pixel statistics of all NDFs listed within the text file files. The ``^'' character indicates that the following string (files) is not the name of an NDF, but the name of a text file from which NDF names should be read.

    % wcsframe '"image_a,image_b,image_c"' sky

This will set the current co-ordinate Frame for the three NDFs image_a, image_b and image_c so that celestial sky co-ordinates are used to refer to positions within the NDFs, if possible.

    % cursor outcat="'first,^list_names'"

This will run CURSOR several times, allowing you to select display positions using a cursor. On the first invocation, the selected positions are written to a positions list stored in file first.FIT. Positions selected on subsequent invocations are written to positions lists with names read from the text file list_names. Finally, if this CURSOR command is followed by:

    % listshow accept

LISTSHOW will display the contents of all the catalogues created previously by CURSOR.

If an application has more than one NDF or positions list parameter, each parameter should be given the same number of values (i.e. data files). A warning is issued if any parameter is given too many values, but processing continues normally until the smallest group is exhausted. For instance, the following example adds NDF a1 to a2, and b1 to b2, putting the results in a3 and b3:

    % add in1="'a1,b1'" in2="'a2,b2'" out="'a3,b3'"

If (say) an extra NDF had been specified for Parameter IN2, the application would have been invoked twice to process the first two pairs, and then a warning message would have been displayed saying that too many NDFs were specified for Parameter IN2.

There is a special case in which this rule does not apply. If only a single value is given for an data file parameter, the same value is used repeatedly on all invocations of the application. So, for instance, if a single NDF had been given for Parameter IN2 in the above ADD example, the application would have again been run twice, using the same NDF for Parameter IN2 on each invocation.

The OUT parameter in the above example could alternatively have been specified as out="'*|1|3|'". Here, the asterisk (*) represents the base-names, a1 and b1, of the NDFs supplied for the first NDF parameter to be accessed (IN1). The following string, |1|3|, means replace all occurrences of 1 with 3, thus giving the final NDF names a3 and b3.