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Making Things See by Greg Borenstein

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User Detection

As I indicated, the process begins when a user enters the view of the depth camera. When the user appears, OpenNI recognizes that a user is present. At this point, the user has not been calibrated and his joint data is not available. OpenNI basically has a hunch that someone is moving around within the view of the depth camera. OpenNI calls our sketch’s onNewUser function.

Depending on the conditions of the scene, this can happen sooner than you might expect. OpenNI can detect the presence of a user even when not much of his body has entered the frame. For example, Figure 4-2 shows a screen capture from this sketch that was taken at the moment OpenNI first detected me. You can see that I’ve barely entered the frame on the left. My ...

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