G4beamline VERSION http://g4beamline.muonsinc.com

G4beamline is a particle-at-a-time simulation program based on Geant4 [1] and optimized for the simulation of beamlines. See the G4beamline User's Guide at the above URL for a description of the program (it is also installed with this distribution).

This brief description only discusses how to use the program, it does not describe how to construct a simulation's input file; for that see the G4beamline User's Guide.

Using the Program

IMPORTANT NOTE: With a viewer selected, NTuple output files are not written. This includes both .root files and ASCII files from vitualdetector-s, xntuple-s, etc.

Several examples are provided in the distribution. They are located in the "examples" directory under the install directory. In Linux and Mac OS X the install directory is usually in your HOME directory; in Windows a Copy of "G4beamline examples" is placed into "My Documents" (Windows Xp) or "Documents" (Windows Vista).

Visualizing the system

viewer=best will visualize the system using OpenInventor; use its File/Escape to go to the next image. The OpenInventor viewer is part of the G4beamline program. For usage hints, see this Appendix.

The "Other" selection can be used to run any other viewer supported by G4beamline and installed on your system (if necessary). See the output from a G4beamline run with viewer=best to see the list of supported viewers. viewer=Other/Wired will visualize the system using the Wired3 viewer [2]. The "Run" button will run the selected number of runs, each generating a .heprep file. When that is complete, the Wired viewer will be opened on the first file; it considers them "events". For usage hints in Wired, see this Appendix.

Using Historoot to Create Histograms

References

 [1] http://geant4.cern.ch
 [2] http://www.slac.stanford.edu/BFROOT/www/Computing/Graphics/Wired/
 [3] http://root.cern.ch

Using the OpenInventor Viewer

Like other X-windows programs, the OpenInventor driver of G4Beamline can operate in either local or remote (networked) mode. Both the X display client and server must have the 3-D display capabilities of OpenGL installed. Operation over a network can be slow, and a good network connection (>1 megabit/sec) is required for useful results.

The Rotx and Roty wheels at the lower left rotate the image relative to the viewer, and the Dolly wheel (Z) at the lower right moves in and out with a corresponding change of scale. The buttons along the right edge do the following:

Arrow	Select pick mode and cursor
Hand	Select move mode and cursor (default)
?	Help (not implemented)
House	Restore display to Home position
House with arrow	Set Home position to be the current display
Eye	Zoom so everything is visible
Gunsight	Not implemented
Perspective box outline	Select isometric or projected display

When the Hand cursor is active the mouse behaves like this:

Left Button	Click and drag to rotate the display. It acts as if there were an invisible sphere surrounding the image, and the mouse movements rotate that sphere in any direction. This is quite different from the Rotx and Roty wheels, and takes some getting used to.
Middle Button	Click and drag to pan the display -- this moves the visible objects around without changing perspective.
Right Button	Brings up a menu with various functions, Draw Styles, and other items. The most useful is DrawStyles/StillDrawStyle/Wireframe which will draw in the wireframe mode rather than as solid surfaces. This permits you to look inside objects, and is considerably faster drawing. NOTE: daughters are not necessarily visible in wireframe mode -- see the Etc. menu item that makes them visible.

The File menu has several useful items:

PS (gl2ps)	Save the current image in PostScript (drawing)
PS (pixmap)	Save the current image as PostScript (pixel map)
IV	Save the current image as an OpenInventor file
Escape	Exit the OpenInventor Viewer. This causes the program to simulate the next run and display the result.

The Etc. menu has several useful items:

Set Solid	Set the G4 mode to Solid (default)
Set (G4) reduced wire frame	Set the G4 mode to wireframe, real edges only
Set (G4) full wire frame	Set the G4 mode to wireframe, including triangles to fill surfaces
Visible mothers + invisible daughters	Daughter volumes are invisible (default)
Visible mothers + visible daughters	Make all objects visible

Note that daughter volumes are by default invisible, so to look inside a solid object you usually need to select wireframe mode and also Etc/VisibleMothers+VisibleDaughters.

The key to understanding how objects are displayed is to know that Geant4 has a solid/wireframe choice, and OpenInventor has a solid/wireframe choice, and they are different:

G4 mode (Etc menu)	OI mode (Right click menu)	Description
Solid	Solid (as is)	Draw solid surfaces
Solid	Wireframe	Draw wireframes with triangles filling visible surfaces
Reduced Wireframe	Either	Draw reduced wireframes, showing only real edges
Full Wireframe	Either	Draw wireframes with triangles filling visible surfaces

For instance, in G4 reduced wireframe mode a sphere is invisible as it has no real edges; in G4 full wireframe mode it has triangles filling its visible surface (in such a way you can tell it is a sphere).

The OpenInventor driver has many more features, but this should get you started. It will also do animation: with the hand cursor left click and drag the image, letting go of the button while moving -- the image will continue to rotate until you left click on it (works best locally).

Using the Wired Viewer

On Windows, the Wired viewer is installed with G4beamline, and is used as the "best" viewer. On Linux and Mac OS, you must install it manually [2] and then make a symbolic link from its install directory to [g4beamline install directory]/Wired -- then you can set Other to Wired and use it.

When the Wired viewer comes up, it displays a few centimeters near the point x=0,y=0,z=0. It may happen that your system has no visible objects there and the display may look blank. On the lower left is a set of icons, and a click on the second one (a "plus sign" with 4 arrowheads) will zoom so that your entire system will be in the display.

The Wired viewer is started with the first image file loaded. At the top of the window is a toolbar with icons for "open", "reload", "previous event", "next event", "up (inactive)", "down (inactive)", "Toggle Automatic Updating (looks like a clock)", "Create New Window", and "Show/Hide Data Tree". On the right side of the window is a data visibility tree that permits you to select individual elements of the simulation and toggle their visibility.

At the bottom of the viewer subwindow are 8 icons and 2 sliders. The icons are:

R	Reset View
+ with arrowheads	Fit in Window
+	Zoom In
-	Zoom Out
+ arrows pointing in	Reset Translation
CCW arrow	Rotate Counter Clockwise
CW arrow	Rotate Clockwise
Circle	Reset Rotation

The left bottom slider translates the image, and the right bottom slider rotates it. The translate slider does not immediately react to reversals of direction. The rotate slider may look like it goes forward and backwards while sliding in one direction -- this is really due to the fact that you are looking completely through the system, and a right rotation makes components behind the center move to the left (etc).

Along the right edge of the viewer are two sliders. The upper one translates the image and the lower one rotates it. The same remarks apply to these.

A right-click on the viewer window brings up a context menu with several useful choices:

Orientation Actions	Perform the above icon actions, plus more. Includes OrientationActions such as TopView, SideView, CenterInWindow, etc.
Orientation Toolbar	Turn the bottom icons on or off
Projection	Select projection (Parallel is the default)
Mouse Function	Select what mouse actions do
Drawing Options	Various drawing options

By selecting MouseFunction/Rotation you can drag the viewer window to rotate it, as in OpenInventor (i.e. the mouse is rotating an invisible sphere containing the system). Similarly, MouseFunction/Translate lets you pan the image using the left mouse buton, as OpenInventor does with the center mouse button.