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## 8 Activation Actions

As well as seeing the overview of table data provided by a plot or statistics summary, it is often necessary to focus on a particular row of the table, which according to the nature of the table may represent an astronomical object, an event or some other entity. In the Data Window a table row is simply a row of the displayed JTable, and in a plot it corresponds to one plotted point.

If you click on plotted point in one of the graphics windows, or on a row in the Data Window, the corresponding table row will be activated. When a row is activated, three things happen:

1. If that row is represented by a point in any open 2- or 3-dimensional scatter plot windows, a visible cursor marker will be drawn centred on that point.
2. If the Data Window is visible, the table will be scrolled to show the row and it will be highlighted
3. If an activation action has been defined, it will be invoked

The first two of these mean that you can easily see which point in a plot corresponds to which row in the table and vice versa - just click on one and the other will be highlighted.

The third one can be more complicated. By default, no activation action is set, so nothing else happens, and this may very well be what you want. However, by clicking on the Activation Action selector in the Control Window you can bring up the Activation Window which enables you to choose an additional action to take place. There are various options here and various ways to achieve them (see Appendix A.10.2 for more details) but the kinds of actions which are envisaged are to display one or more images or spectra relating to the row you have identified. One of the options available for instance retrieves a postage-stamp image of a few arcminutes around the sky position defined by the row from a SuperCOSMOS all-sky image survey and pops it up in a viewer window. So for instance having spotted an interesting point in a plot of a galaxy catalogue you can click on it, and immediately see a picture to identify its morphological type.

The exact actions you want to perform may be closely tailored to the data you have, for instance you may have a set of spectra on disk named by object ID. It's impossible to cater for such possibilities with a set of pre-packaged options, so you are able to define your own custom actions here. This is done by writing a expression using the syntax described in Section 7. A number of special functions (described in the following subsection) are provided to do things like display an image or a spectrum in a browser (given its filename or URL), or access data from certain data servers on the web, but there is nothing to stop the adventurous plugging in their own external programs so in principle you can configure pretty much anything to happen on the basis of the values in the row that you have activated.

- 8.1 Activation Functions

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@bristol.ac.uk