SADT: The Survey Areas Definition Tool

What is SADT?

The Survey Area Definition Tool (SADT) is a tool that generates the pointing positions for each tile within a VISTA or VST survey. In addition, for VISTA, it searches the guide star catalogues and selects the suitable sets of guide and active optics stars necessary to observe the individual pawprints of each survey tile. In the case it does not find a sufficient number of guide stars or active optics stars, the tile position is slightly re-adjusted and the tool searches automatically again for suitable AG/AO stars. The output of the SADT (survey area file in XML format) must be used together with the web-based p2 tool to generate the Observing Blocks (OBs) for observing runs scheduled on the VISTA or VST telescope.

Important notes concerning releases

The current public release of SADT is version 5.1.0 of the software for VIRCAM and OmegaCAM observations.

Version 5.1.0 is a unified SADT version that can be used for VIRCAM and OmegaCAM. Some bugs in previous versions were fixed. A feature for the VIRCAM case is the possibility to search for guide stars in the first pawprint of a tile 6 pattern only. This is meant for observations with short exposures, for which a very accurate guiding is not necessary. The advantage might be that a smaller number of backtrackings is needed in areas where there are only few guide stars available.

Previous release notes

SADT v5.06: a version of SADT for observations with OmegaCAM at VST only. It has been tailored for the preparation of survey areas for early science observations of the Public Surveys. Some specifics of this SADT release for VST are:

  • the position angles of the detectors on the sky can be set to any value;
  • a definition of an area as geodesic rectangle is not offered, coordinate ranges or circles should be used;
  • the positions of guide and active optics stars are not propagated to the OBs. Thus, please use SADT for VST without the option 'Find Guide/aO Stars'!


SADT v5.04 (for VIRCAM/VISTA observations): includes the extension of the 2MASS catalog to the visible wavelength. A synthesised I-band magnitude, which corresponds to the response of autoguider and wavefront sensor CCDs, is calculated from the 2MASS JHKs colours. The new magnitude limits in the sadt.cfg file correspond to this I-band magnitude and were tested on sky. It is recommended to use the extended 2MASS catalog for the search of guide and wavefront sensor (aO) stars.  After the re-coating of the mirror, the magnitude limits of the guide and aO stars remain the same as since Period 87. Thus, some fields at high Galactic latitudes still may suffer from frequent backtracking or even failures of aO star searches. Solutions are to try and make a small shift in DEC, since backtracking is only done in one direction, or to try using another catalog.

Supported Platforms

The latest version of the Survey Area Definition Tool (SADT) is available for Scientific Linux running Java 1.6 or higher. It is known to work also under other Linux flavours, but not all have been tested. As a Java application it should also run under Unix, Mac OS X, or MS Windows operating systems running Java 1.6+, but no support is guaranteed on other systems.

SADT Distribution

The SADT can be retrieved via anonymous FTP:

How to use SADT

Instrument selector

This page is specific to Public Surveys on the VST and VISTA telescopes.