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19. 07. 2006  10:56 | 03_Sketches_&_Projects_4

Video Tracking System of Spatial Configurations

The very first version of the "Video Tracking of Spatial Configuration (VTSC)" system developed by fabric | ch was delivered to Julien Nembrini from the EPFL. The system allows to control an unlimited set of volumes in a given space and allows to detect if a given volume is filled or not. A volume is obtained by a set of different USB webcam's point of views (shooting the same room from distinct locations for example). Intersections of defined zones in these point of views define volumes.
The system is working with a set of basic USB webcams. Each USB webcam is controlled by a dedicated application. The application managed 2D zones that must be monitored in the image obtained from its associated webcam: it detects if a zone was activated or not (filled). All these applications are networked (meaning that the controlled volumes can even be in distinct remote locations), all information centralized to a main controller application known as the moderator. The moderator is filtering received information and decides if a volume is activated or not (filled).
Within the framework of this project, a volume activation will suggest epfl's e-puck robots to organised themselves in a given configuration.

As the system is networked based, it can be deployed in a very convenient way. The number of involved USB webcams, the number of needed computers, the location of these computers can be adapted very easily to any kind of project/configuration. As mentionned previously, it is even possible to combined the monitoring of volumes that are not at the same location in order to control something else in another distinct location. It can also be easily integrated in the Rhizoreality system developed by fabric | ch..
A set of tests we have made has raised a set of limitations/observations to take in consideration while deploying a VTSC configuration. We have successfully plugged 4 USB webcams on the same computer (PC laptop, desktop) by using a USB HUB. Of course, application in charge of controlling a given webcam must be installed and runned on the same computer as the webcam (the video stream is not broadcasted). So one basic computer was able to host 4 applications for video image analysis and the moderator without any major frame rate loss.
One must kept in mind some USB limitation linked to cable length (around 10m max.). It should be possible to connect the webcam with a longer cable through the use of USB repetor or USB to RJ45 convertor but these options were not tested or used within the frame of this project.
Of course the more powerful the host computer is, the more it should be possible to connect webcams, keeping in mind that the USB bus has its own limitation in term of bandwidth which should of course restrict the number of camera that can be connected to the same computer without video signal or major frame rate loss.
The system is based on JAVA but video signals are accessed through DirectX, so VTSC is condemned to run under Windows. Things can evolve in time, through the change of the webcam's video signal access module.

Posted by fabric | ch at 19. 07. 2006 10:56