Originally, only a command line solver GSvit was released. Benefits of a command line tool are namely seen when you want to do some scripting, or you are using remote access to some high performance computing system. To use GSvit via command line, typically a parameter file is set up in a text editor (or e.g. via some script) and then it is passed as an argument to GSvit solver. So this is how typically invoking GSvit looks like:
where parameter file is a simple text file including directives like
for assigning calculation to 8 cores of the processor. See GSvit input files description for more details.
For complex simulations the parameter file can contain many directives. To assist with setting up the parameter files, later a simple parameter file viewer XSvit was added, which also has some basic functionality in running the calculation (calling GSvit) and visualising some of the results. It still operates only with the text parameter files used in GSvit so it does not harm the possibility of using any text editor for further parameter files modifications. After invoking XSvit the same can be done via graphical user interface as shown below.
In documentation related to FDTD calculations via GSvit, which lists all the possible options and algorithms, both the parameter file setup and XSvit based setup is always mentioned. There are also sample parameter files to be directly used for further modifications, either via XSvit or a text editor.