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## 9 Tool Interoperability

TOPCAT is able to communicate with other tools using one or other of two messaging protocols:

- SAMP (Simple Applications Messaging Protocol)
- PLASTIC (PLatform for AStronomical InterConnection, not available in the Debian version)

An example of the kind of thing which can be done might be:

1. TOPCAT sends a catalogue to an image display tool
2. The image display tool shows the catalogue entries as markers placed appropriately on a displayed image
3. User actions which highlight one of the points in one tool can then automatically highlight the same point in the other

Examples of the kind of tool which TOPCAT can interoperate with in this way are image analysis tools (Aladin, GAIA, ds9) table analysis tools (VisIVO, STILTS, other instances of TOPCAT itself), spectrum analysis tools (SPLAT, VOSpec), sky visualisation tools (World Wide Telescope, VirGO), scripting languages (SAMPy), and others.

SAMP and PLASTIC do much the same job as each other, and work in much the same way. SAMP is an evolution of PLASTIC with a number of technical improvements, and PLASTIC has been deprecated in favour of SAMP since around 2009. PLASTIC is therefore of mainly historical interest and not implemented in the Debian version.

The communication architecture of the two protocols is basically the same: all tools communicate with a central "Hub" process, so a hub must be running in order for the messaging to operate. If a hub is running when TOPCAT starts, or if one starts up while TOPCAT is in operation, it will connect to it automatically. If no SAMP hub is running, TOPCAT will set one up during application startup.

This communication has two aspects to it: on the one hand TOPCAT can send messages to other applications which causes them to do things, and on the other hand TOPCAT can receive and act on such messages sent by other applications. The sent and received messages are described separately in the subsections below. There are also sections on the, somewhat different, ways to control and monitor messaging operatiion for the cases of SAMP and PLASTIC.

- 9.1 SAMP control
- 9.2 PLASTIC control
- 9.3 Messages Transmitted
- 9.4 Messages Received

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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@jiscmail.ac.uk