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Triggering/ Sensor Environment

Each space is equipped with David Rokeby's Very Nervous System [VNS] (both hardware and software). The Very Nervous System is explained a bit more below -- but essentially in this context it is being used to sense motion in the space and translates this into a form of computer data -- what we refer to as "movement data". It is possible to send this movement data generated by the VNS to the other space at between 1 and 10 ms of speed. This nearly real-time, as compared to the video stream which arrives in the other space after an 8 second lag time. The data can be used in either or both spaces to trigger sound, video imagery, lighting changes, etc. (see Working with Software for more information).

Questions and Answers:

Question #1: provide a simple and clear explanation of how the Very Nervous System works, "differencing" and the concept of triggers.

Answer: The very nervous system is a motion analysis system consisting of two parts: a hardware "frame grabber" video processor and a software analysis program. The frame grabber digitizes video and makes this digital information available to the analysis program (60 fields per second for VNS III and 30 frames per seconds for soft VNS). The analysis program then can deliver different types of information about what is happening within the video frame to the user, frame by frame (or field by field in some cases). This is includes - how many pixels have changed from dark to light (differencing), how many dark pixels have remained in concurrent frames (presence), or the 2-D position of the highest dark pixel in the frame (head tracking). Triggers are user defined zones within the analysis frame that are analyzed individually. The results of the analysis for these user defined regions are made available to the user as separate output. Thus the user can draw a box around a specific region within the frame, and the very nervous system will report on the activity within the box separately from other analysis output. (John Mitchell)