Black spot in registration mode

The stereo camera I used was Obbrec stereo astra s and I tested the function with OpenNi SDK.
When i got the depth image with the registration function opened, I got a image with black spot on the depth image, just like the picture attached.

My question is:
(1) Does the black spot equal to the projector’s pattern? If not, what is the black spot?
(2) I also want to know how the IR image register to the depth image because their F.O.V seem different from each other.
Thank you