AROcclusion README - Sep 21 2011, Aurel Wildfellner

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|   INTRODUCTION   |
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This project holds a modified version of ARToolKit, to support the streaming of video over OpenNi, for e.g. from the kinect sensor. In addition a registered depth image can also be retrieved. A simple test application is also included, which demonstrates proper rendered occlusion of virtual objects.

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|     BUILDING     |
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You will need a working OpenNi development version installed , to build ARToolKit.

./Configure 
    Select '6' for OpenNi
    yes
    yes
make

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| VIDEO INTERFACE  |
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include/AR/sys/videoOpenNI.h defines several functions to extend the video.h interface for handling a depth image. Implemented in lib/SRC/VideoOpenNI/.

ARUint32* arVideoGetDepthImage(void); -- Use this to get the registered depth image. The value encodes the distance from the sensor in millimeters. 0 for undefined.

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| DEPTH BUFFER CONVERSION |
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For applications as proper occlusion of virtual objects, you may need to convert the range image obtained from openni to a OpenGL zbuffer. 

Computing this directly might be the only proper solution, however the current does this rather different.

Run ./bin/calib_openni (follow the instructions)
    Place the marker in the middle of the screen at the red dot.
    Press s to take a 'sample'.
    Now place the marker at a different distance from the camera and repeat the last steps.
    Do this in 5-10 cm increments in the entire depth-range, which you want to measure later on.
    Save the two sample vectors, which are printed after pressing 'esc'.

Use the two vectors to fit a polynomial function (good results with degree 4). You can do this with octave:
    polyfit(kinectD,zbufferD,4);
Use this function for conversion (see openniTest.c for example).


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|       OPENNI TEST       |
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Print out the standard 'Hiro' marker.
Run ./bin/openniTest
A cube appears on the marker.
If you place any real object in front of the cube, it gets occluded by it.
Be careful not to occluded the marker itself with the real object.