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Stereo Sehen

Stereo Sehen

Evi Kruckenhauser

A U10 project by NGBK, BVG, and the Berlin Senat

A video combines the driver’s view of a Berlin subway train with the constructed view of the parallel route on the surface. 8 Monitors were installed in a subway cart and the video presented in quasi-realtime as the U2 line went back and forth between Alexanderplatz and Gleisdreieck. To match the view with the actual train speed, the position of the train had to be continuously compared with the video. While the initial request asked for the automation of this task, in the final performance this was done manually, as it became clear that the video would only be shown on a single day (while implenting the automated version would likely have taken multiple days).

The video player was implemented in MaxMSP/Jitter. Many thanks to link for outlining basic strategies how to optimize video playback.

As a controller the 3dconnexion SpaceNavigator was chosen to adjust the playback speed. We also tapped the speed signal from the train which was implemented as a current loop across a Zeigerinstrument. An optocoupler was used at this point to ensure isolation between the train’s power (100V DC for most of the internal systems). Its (input-side) LED was inserted in the loop, while its (output-side) photo-transistor modulated the amplitude of a sine-wave from the laptop’s audio output and fed it right back into the audio input. No traditional sensor interface was used to avoid potential problems with lost serial links due to disconnected USB lines (I had to walk a lot (and fast!) between both ends of the train with laptop in hand). Linearity wasn’t very good with this simple setup, but we basically wanted to detect when the train started and stopped.