Robust people detection | opencv | c# | unity integration

Hello,
i'm looking for robust opencv solution for reliable people detection.

The camera will be placed at the entrance of a buiding on the ceiling above the people.
The peopole are standing in front of an screen which runs a untiy 3d application.
The unity 3d application should receive inputs from the camera/opencv.

The following infos are needed:
- Number of persons visible
- location of the persons (rough would be enough, e.g top-left, top-center, top-right, middle-left and so on)
- flow-direction of the persons (if possible - topleft -> top-middle, ...)

The results should be available / integrated in unity 3d.
I read about Emgu (http://www.emgu.com/wiki/index.php/Main_Page) or using opencv as staticaly linked plugin in unity.

Thank you
Markus Heiss