For the latitude, use negative for south.  The valid range is
-90.0 to 90.0.

For the longitude, use negative for west.  The valid range is
-180.0 to 180.0.

The radius specifies how many degrees out from the specified
latitude and longitude is considered within the site.  Floating
point numbers are allowed here.

The step size specifies how many seconds the propagator will jump
between data points.  The larger the number, the quicker the program
runs but the cruder the data that are generated.  If the data are too
crude, encounters will be missed.  The step size should always be
small enough so that the space craft will not travel more than the
specified radius number of degrees in the specified step size number
of seconds.