I want to show the starting position and direction of the shooting on a 3D map. I am wondering how I can get these information and save them for my demonstration?
There are probably some history data saving libraries (Root perhaps?) that might already do what you want to do, I haven’t worked with them directly. But if you just want some initial particle information saving to be used by your own custom code you could do so in your Primary Event Generator function.
You can also get to the primaries in your UserEventAction::EndOfEvent() code. Unlike the tracks, the primaries do not get deleted until after the event is closed.