This manual introduces SaVi to the user. Other documentation is available for SaVi in textfiles supplied with the SaVi software:
Further information on SaVi is available on the web at http://savi.sourceforge.net/.
Geomview provides SaVi with three-dimensional rendering capabilities. When using Geomview, the Look, Fly and Rotate buttons in its toolbar are the most useful; the stationary axes allow you to see the Earth rotating against something fixed as you spin your camera view around. Documentation for Geomview, describing Geomview's many features, is available separately on the web at http://www.geomview.org/.
Note that SaVi has a number of simple command-line options that can be seen by typing:
./savi -help
which provides brief summary documentation of the options.
Below is a brief guide to the main features of SaVi's graphical user interface:
The main window is where satellite parameters are edited and where Geomview (if it is in use) is controlled from the Rendering menu. The simulation is run forwards and backwards in time using the >> and << buttons on the playbar at the bottom of the window. > and < step forwards a single interval of time; the default time interval is set to sixty seconds for each step, and can be changed here.
Main window - to see this, launch SaVi.
Resizing this window vertically to stretch it to see information on more satellites is a good idea.
Double-click a line listing satellite parameters to open the 'Edit satellite parameters' window and edit values directly. Press return after entering each value to update the satellite and change the simulation. A custom list of edited satellites can be saved for posterity as a script to be loaded in again later - see the File menu in the main window's menubar.
The menubar's Edit menu allows you to copy, cut and cut satellites, or edit existing or new satellite parameter lines, via an edit box. Like all SaVi windows, this edit box can be left open while other windows are active. The edit box will always show parameters for the currently-selected satellite.
Edit window - to see this, use the Edit menu, or double-click a satellite
parameter line.
Individual satellites and their coverage can be hidden from view here, by using the checkboxes.
Simulations constants can also be edited from the Edit menu. Altering these from Earth normal is not for the faint of heart.
Simulation constants - to see this, use the Edit menu.
The menubar's Views menu allows you to open the coverage panel and fisheye window, discussed below. Opening the coverage panel is often the first thing you do upon launching SaVi. Other options in the Views menu duplicate the playbar at the bottom of the window, including the 'Restart' button to reset the clock to time 0.
The Constellations menu allows you to load in simulations of known satellite constellations, both existing and proposed. The simulations on this menu are split into several groups:
Note that loading in a constellation from the menu replaces all existing satellites. To add a constellation to existing satellites you want to preserve, use Load... in the File menu, and load in a Tcl script from SaVi's data/ directory. To save an existing constellation you have created, such as one generated using the Ballard rosette tool, use the File menu's Save satellites as Tcl script... option. To begin from scratch, either delete all satellites, or select Empty space, and confirm the dialog that comes up.
Empty space of satellites dialog - to see this, use the Constellations menu.
The Rendering menu includes a Real-time mode option that attempts to synchronise SaVi to the computer's clock, so that an interval is simulated every second. If you set to 1 second per interval, SaVi attempts motion in real time. This mode option is most useful on very fast computers.
The Rendering menu is complete when SaVi is running with Geomview. The full menu allows you to control how Geomview shows the constellations in its Camera windows. To change the satellite type shown in Geomview, select a marker type from the top section. To restore the default green dots, select that marker type again.
By turning off Show central body, an outline Earth is produced. This is useful when used with Geomview's spherical projection (in the Geomview window's Space menu.)
Animate in Geomview can be turned off temporarily if Geomview becomes problematical, so SaVi can be used standalone. This option is useful on slower computers.
The Help menu identifies SaVi and provides brief installation information.
The coverage panel is where most viewing work in SaVi is done. It is likely that this will be the first option selected once SaVi is running, and that most work will be done using the menubar at the top of this panel's window.
Coverage panel - to see, use Views menu on main window.
In the coverage panel a map projection of the Earth and visible coverage is shown. The Earth map can be either 600x300 pixels or 1024x512 pixels in size. Stretching this window horizontally will show two projections side-by-side; this is useful for looking at coverage at the edge of the map, which lies in the middle of the two copies.
A number of different map projections can be chosen:
Clicking in the map sets coordinates that are passed to the fisheye window, and can then be set in that window.
Satellite coverage (which defaults to yellow/red) is intended to give an idea of the number of satellites visible from a point, or available diversity. The higher the number of satellites covering a point, the deeper the shade of red.
Interval decay (which defaults to shades of blue) is intended to give an idea of where a satellite footprint has been and is going, even when you look at a still map snapshot. Turning this feature off replaces blue with white.
Map colours can be controlled to taste by the Shading menu or by clicking the colour wells in the key individually to launch a colour selector. 'Change shading' will always produce ranges of tasteful hues.
The satellite selected in the main window will be shown in the coverage panel as purple, rather than green, as will its groundtrack.
Still map snapshots can be saved from the File menu. A simple ppm bitmap format is used, and compressed with gzip. These files can be read directly with The Gimp (GNU Image Manipulation Program, available from http://www.gimp.org).
The coverage of all satellites is controlled in the coverage panel by angle, pop-up menu, and slider. The angle is between 0 and 90 degrees. The angle can either indicate mask elevation - the minimum angle through the atmosphere needed to establish communications with the satellite - or the angle of the satellite beamwidth. The default mask elevation is generally more useful. The slider to the right alters the angle value directly.
Computed coverage estimates are currently not accurate, and vary between projections.
The playbar is repeated at the bottom of this window for convenience.
The fisheye window shows a view of the sky looking upwards from the ground, with the horizon around the outside of the circle. North is to the top of the fisheye. The default location is at zero point (zero longitude, zero latitude, zero altitude, just off the coast of Africa).
Fisheye panel - to see, use Views menu on main window.
The fisheye window is completely resizeable, and will scale the fisheye area to suit. A larger fisheye shows a large number of satellites in view much more clearly.
If ground terminal mask elevation is selected from the coverage panel, the mask circle will be shown, and the time a satellite spends in view (i.e. within the mask area) will be indicated next to the satellite. Note that times are only accurate to +/- half the simulation interval, assuming that a satellite began moving in the fisheye outside the mask area. Setting a smaller simulation interval provides more accurate time-in-view estimates.
Enter new coordinates updates the fisheye to use the values in the white text boxes, which will be copied to the actual coordinates in the blue area below.
Reverse fisheye view switches East and West, to give an idea of satellites moving over the Earth. This can be compared with Geomview's spherical view with the central body turned off, mentioned earlier.
The best, most accurate, way to simulate a custom constellation in SaVi is either to:
The background colour in Geomview is set at the start of savi/oogl/savi.oogl.
0 0 0 is black.
255 255 255 is white.
Geomview can have multiple cameras open showing different views. Scripting of camera actions in Geomview (using its oogl object-oriented graphics language, which is a degenerate form of lisp) can be very powerful.
Notes on sources and for and details of simulated constellations can be found in the comments to each constellation script. See the /home/lloyd/savi/data directory.
SaVi and Geomview together are much more robust on glibc-based unix-like systems (e.g. Linux), and running SaVi and Geomview in a proper unix environment is recommended.
SaVi without Geomview is more robust than the combination of both, particularly on systems not using glibc. Geomview's pipe handling is currently very weak under e.g. Cygwin, where glibc's fopencookie code is not available. On these systems, Geomview can be made to fail with a 'can't seek back on pipe' error by either:
Work on Geomview to address this problem with Geomview, and to bring Geomview up to date with modern compilers and libraries, is ongoing.
Further information on SaVi is available on the web at http://savi.sf.net/