4.6  :  TOPCAT Access to the Millennium Database

An alternative to the remote access methods on the previous pages is to use Mark Taylor's TOPCAT tool that was originally developed for StarLink. TOPCAT is a VO aware, interactive visualisation toolkit. It is similar in philosophy to the VOPlot tool that is available as an applet off the main web interface. TOPCAT is written in Java and runs as a standalone program on any machine that has a Java Run Time Environment installed. The tool can be downloaded on the indicated links in either a full or a lite version. The tool can read tabular files in various formats, including CSV, as long as there is at most a single header line with column names on top. It could therefore conceivably be used on the result of a wget query, as long as the comment lines are stripped on before reading into TOPCAT.

With a lot of help of Mark Taylor, GAVO has written a Java plug-in to the TOPCAT tool that allows users to query the GAVO Millennium web site directly and loads the results into TOPCAT for visualisation. Since version 3.3 of TOPCAT this plugin is part of the TOPCAT distribution.

When clicking the "Open file" button or menu item an special button is available, that, when clicking, allows the user to write an SQL query and send it to the appropriate web application. The button is indicated in red in the following figure.

Clicking this button opens a query dialogue:

Once the query is executed the result is automatically loaded into the tool and is available for plotting:

Nice features of TOPCAT are its 3D capabilities and that one can assign color based on a column: