It is necessary to carry out the procedure described in 8.1 Setting up Atlantis ↔ Interactive Athena communication The actual vertexing algorithm type is chosen in myTopOptions.py. The picture below shows the vertexing process.
Tracks whose IDs are to be sent to the Athena vertex fitter have to be selected with the "rubberband" Atlantis interaction. After doing so, a pop-up menu appears on the canvas where the user selects New List, into which these tracks are put.
The most recent list is now highlighted in the Atlantis List manager dialog window.
If only Track tracks were put into the list (and no other objects such as hits or tracks of other types), an item Vertex in Athena appears in the context menu after right-clicking on the list item in the List manager.
Only with Track tracks one can call the Athena vertex fitter. The Atlantis internal vertex fitter can be called upon Track tracks and iPatTrack tracks.
Given that proper information was filled in the Atlantis Interactive Athena dialog and the connection to InteractiveServer.py could be established, the Track tracks IDs were sent to Athena and the fitter called. This can be observed in the window where Athena is started from.
In order to find out whether or not the listed tracks come from a common vertex, the user has to hit the Get Event button and search for a new item of the RecVertex datatype (see event summary in the output window in the bottom part of the GUI or File → Event Properties) once updated event data arrive. If the vertex was found and the RecVertex datatype is switched on (Data tabpane, InDet) a newly calculated vertex will be displayed for instance in the XY projection as an ellipse. The tracks which form this vertex will be shortened to the centre of that ellipse (in XY).
The picture below demonstrates the aforementioned procedure.