Elphel have a very interesting piece on a 4-camera approach to real-time mid-range RGBD. The core of the approach is to use block matching, and to target sub-pixel accuracy and to avid intermediate representations. To see a demo of their results try their scene viewer . Click on a picture on the left, then a numbered link under the thumbnail and play around with the RGBD image.
I think this is potentially a great platform for mid-range (5-200m) depth mapping in the optical domain, which can then be used in a variety of methods. A simple one would be to provide labelled data to support occlusions in people tracking, but I think there’s a lot more here.
[Image above from elphel Thanks Andrey!]