As far as I know, for real-time tracking data transfer Vicon supports VRPN protocol and maybe has its own proprietary communication protocol, too. Slicer understands OpenIGTLink protocol. So you need to convert between these two protocols. PlusServer application in Plus toolkit can do protocol conversion for many devices, so it would not be too difficult to add conversion from VRPN or Vicon’s own protocol. Or you can develop a converter on your own, which receives messages from Vicon and sends them to Slicer using OpenIGTLink.