openni_tracker for multiple users

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Hi,

I have previously done skeleton tracking using openni_tracker with only one user. Interestingly, openni_tracker can also detect multiple users and hopefully track them. I have tried doing it but the following problem occurred.

1. It detects users 1 and also detects his Psi pose.
2. When the second user comes into the frame, it detects second user but does not detect his Psi pose
3. It does not start tracking any of them.

Here is what happens:

Any one who can possibly comment on the correct usage of openni_tracker for multiple user tracking is welcomed.