From the main menu, choose "Files" and then ".gdml".
At least the two examples gdml files coming with the app should appear : lhcbhcal.gdml and lhcbvelo.gdml. Select for example lhcbvelo.gdml. You should see :
By default, after having read the file and created the Geant4 geometry tree, a visualization in wire-frame is done for the levels "1,2,3" of the geometry tree (then excluding the "mother volume" level 0). Default colors are : leve 1 in yellow, 2 in cyan, 3 in magenta.
You can change the white background with the GUI steps :
You can have a top view of the "VELO detector of LHCb" with :
See the "Camera panel" section for more about the camera.
From the main menu, activating the "geom" item leads to a panel permitting to have more interactive customization of a scene graph (sg) created from a loaded geometry tree. For example you can have some solid volumes by doing :
With this setting levels 1,2,3 are visualized with the volumes in the level 3 done in solid.
WARNING: a Geant4 geometry tree could be something fat to process due to the "russian dolls" structure that may induce a lot of volumes. To protect against potential bottlenecks the "max time" item permits to limit the time of the construction of the scene graph (5 seconds by default) and "max shapes" limit the number of shapes (10000 by default).
Various coloring strategies are proposed through the "atb per" item.