depth of kinect

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Hello, I use the ununtu and openni.

I'm looking at the kinect depth value.

(http://www.ros.org/wiki/kinect_calibration/technical).

There is "Disparity to depth relationship".

Is it open-kinect or openni or both relationship?

I want to know depth value and compare the actual distance.

(http://mathnathan.com/2011/02/depthvsdistance/)

The hompage' host used libfreenect driver.

Can anyone tell me how to obtain depth value or disparity value in ubuntu, openni

driver?

Is it possible extract the distance or disparity in a particular point ?

Thanks.