Finding depth

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Hi, Since quite a few days i'm stuck on this problem. I have calculated all the Intrinsics and Extrinsics of my cameras and also gotten the disparity map of two images captured from each.However i am not understanding how the disparity map help in depth perception.Like how can we obtain the z-coordinate (w.r.t camera) using the disparity map or do I need to do some further steps to obtain the depth. Please help..