Virtual Observatory Software for Astronomers

Introduction to TOPCAT

TOPCAT is an interactive graphical program which can examine, analyse, combine, edit and write out tables. A table is, roughly, something with columns and rows; each column contains objects of the same type (for instance floating point numbers) and each row has an entry for each of the columns (though some entries might be blank). A common astronomical example of a table is an object catalogue.

TOPCAT capabilities

TOPCAT can read in tables in a number of formats from various sources, allow you to inspect and manipulate them in various ways, and if you have edited them optionally write them out in the modified state for later use, again in a variety of formats. Here is a summary of its main capabilities:

  • View/edit table data in a scrollable browser
  • View/edit table metadata (parameters)
  • View/edit column metadata (column names, units, UCDs...)
  • Re-order and hide/reveal columns
  • Insert 'synthetic' columns defined by algebraic expression
  • Sort rows on the values in a given column
  • Define row subsets in various ways, including algebraically and graphically
  • Plot columns against each other in 1, 2 and 3 dimensions, distinguishing different subsets
  • Calculate statistics on each column for some or all rows
  • Trigger a configurable action (e.g. object image display) when a column is selected
  • Perform flexible matching of rows in the same or different tables
  • Concatenate the rows of existing tables to create new ones
  • Acquire tables from web services, external filestores or other customisable sources
  • Write modified tables out in original or different format

General concepts

The general idea of the program is quite straightforward. At any time, it has a list of tables it knows about - these are displayed in the Control Window which is the first thing you see when you start up the program. You can add to the list by loading tables in, or by some actions which create new tables from the existing ones. When you select a table in the list by clicking on it, you can see general information about it in the control window, and you can also open more specialised view windows which allow you to inspect it in more detail or edit it. Some of the actions you can take, such as changing the current Sort Order, Row Subset or Column Set change the Apparent Table, which is a view of the table used for things such as saving it and performing row matches. Changes that you make do not directly modify the tables on disk (or wherever they came from), but if you want to save the changes you have made, you can write the modified table(s) to a new location.

Quick Start

If you launch the application, you will find that it has a full internal help system. Head for the "quick start guide". You can load a demonstration table from File/Load Table/Examples. There are several astronomically useful examples.

Acknowledging AstroGrid. If you make use of the AstroGrid system or tools, we would be grateful if you could acknowledge this use in any resulting publications. You could use these words: 'This research has made use of data obtained using, or software provided by, the UK's AstroGrid Virtual Observatory Project, which is funded by the Science and Technology Facilities Council and through the EU's Framework 6 programme.' Use of any data discovered or accessed through AstroGrid should of course be mentioned as noted by the data providers.

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