13 Interaction Mode

We have seen the different co-ordinate systems Kappa uses. Now we address how the applications obtain co-ordinate information itself. Applications often permit a variety of mechanisms for obtaining those co-ordinates. Typical possibilities are as follows.

Catalogue

— In this mode the application reads a file containing a positions list. This can either be a FITS binary table, or a text file in STLformat, and can contain WCS information allowing positions within the catalogue to be aligned with other data. Positions lists can be created by several applications such as CURSOR, LISTMAKE, CENTROID, etc.

Cursor

— This mode utilises the cursor of the current graphics device. For this to work the array must already be displayed as an image, or a contour plot, or line plot (provided the application handles one-dimensional data), and the picture is stored in the graphics database.

Interface

— This mode obtains co-ordinates from the parameter system, usually in response to prompting.

File

— In this mode the application reads a text file containing a list of co-ordinates in free format, one object per record. There may be commentary lines in the file beginning with # or !. The format and syntax of the files are ad hoc, and are described in the application documentation.

Applications that permit these options have a parameter, called MODE, by which you can control how positional data are to be acquired. It would be tedious to have to specify a mode for each application, therefore Kappa has a global parameter—the interaction mode—to which each application’s interaction-mode parameter is defaulted. The global value remains in force until you change it by assigning an application’s interaction mode on the command line. The following examples shows the effect of the global parameter. For compactness GLOBALS will merely show the interaction mode.

First we display an image on the xw windows device.

Now we obtain the centroids of a couple of stellar/galaxian images via each of the interaction modes. First in cursor mode. Note that CENTROID obtains the name of the input NDF from the graphics database in this mode. If you need to preview which NDF is going to be selected use the PICIN command.

If we look at the global parameters again, indeed we see that it has become cursor mode.

Now we’ll see the effect of changing the mode parameter. Note that unless it is undefined or the application does not support the current mode, you must change the mode on the command line. First we shall prompt for the co-ordinates. A null ends the loop.

Finally, we can create a text file called starlist.dat and run CENTROID in file mode.

Such co-ordinate files can also be created interactively with images by CURSOR.