RSS Slitmask Management Tool (RSMT)

You can download the RSS Slitmask Management Tool from the software downloads page.

Please also see the MOS page if you’d like to try the experimental new mask preparation software, which features several improvements over the RSMT. The MOS page also contains other essential tips and tricks for preparing MOS observations.

Note: RSMT absolutely requires that JAI (Java Advanced Imaging) is installed on your system. JAI can be downloaded from

See for installation instructions.

The installation instructions for Linux (which you should try for macOS as well) mention a directory “$JRE” or “$JDK”. In order to find out what this directory is, start by executing

which java

in a terminal. This should return something like


which in all likelihood is a symbolic link. So use

ls -l /bin/java

(where /bin/java must be replaced with whatever “which java” returned) to check whether the target of the link is yet another link or an actual file. Repeat this procedure until you get to a link whose target is an actual file.

Assume that this file is located at /some/platform/dependent/path/bin/java

Then /some/platform/dependent/path is the directory to use for $JRE or $JDK.

Chances are that you get an error like

tail: cannot open `+245′ for reading: No such file or directory

when running the installation script. If so, open a bash shell, execute


and then try again.

If all else fails, download the CLASSPATH installation, unzip/untar the downloaded file and copy the jar files from the lib directory into




And if that still doesn’t work, consider paying a visit to your local IT gurus. (But also send an email to, please.

Important: Due to what seems to be a JSky issue, RSMT versions prior to 1.912 may calculate wrong RA/Dec values. Please use version 1.912 or higher. Also note that a PC matrix is not supported for world coordinate definitions in FITS files.

Important: JAI (and hence the RSMT) under Windows is running with 32-bit Java only.

Important: The RSMT might not run under Windows 7.

Note regarding Position Angles (PA) of the MOS masks: due to the way SALT operates there are restrictions in the available PAs for any given RA,DEC. You may find the required information in the SALT Position Angle Visibility document.

Just contact us in case you have any questions about this.