Several windows in TOPCAT allow access to standard Virtual Observatory (VO) services. These share the idea of querying the Registry for suitable data services, selecting one of the services thus returned, and then submitting one or more queries to that data service to generate a tabular result. These ideas are explained in more detail in Section 6, while the current section describes the windows. The next subsection describes the components from which these windows are put together. All the windows contain a registry query panel to select a suitable data access service. The positional query windows also contain either a single or a multiple search panel, and the TAP window contains its own custom panel, to define the actual query or queries to submit to the selected service. The windows themselves are described in the following subsections.
TOPCAT also provides access to two important services provided by the CDS (Centre de Données astronomiques de Strasbourg): the VizieR Catalogue Service Query and CDS X-Match Upload Window. These are not strictly speaking Virtual Observatory services, but since they provide access to the comprehensive VizieR archive of astronomical tables they can provide similar or superior functionality to their VO counterparts, so it's worth being aware of them.