I fail to see the relevance of these to the topic?
Especially the Hololens which is mostly hype and hot air than an actually working product.
You brought up the CastAR, don't blame me
Wasn't me, that was Dongulus.
As for the Hololens, they demonstrated it on the last E3 and offered hands on tours, pretty cool ones BTW. So it IS a working product. But not in production just yet. (well it's in production but by the hundreds for now, still it feels imminent for a consumer release).
I think nobody said that it isn't working product, but from the reviews that I have seen, the device suffers from a very poor field of view (~30 degrees) and really poor contrast due to the way it works - basically a projection on a semi-transparent surface acting as a combiner. I.e. good luck trying to use it in a normally lit room. There is a reason why all their demos were done in carefully controlled conditions and darkened rooms. It is nothing at all like the bombastic PR they were trying to present it with.
The Light Field takes it a bit further allowing you to focus anywhere within the stereoscopic images, making it true holo effect, for that we need higher res displays, but it will come, the tech is done.
Those are nowhere near anything usable - lightfield rendering is an enormous bandwidth and processing hog. That's also why true holography (not the Holywood Star Wars/Pepper's ghost or Microsoft's "holography") cannot be done in real time so far - same problem (hologram is a recording of the entire lightfield).
Zebra Imaging has made some very major advances there - they have holographic printers and they claimed to have a true real time holographic display as well:
http://www.zebraimaging.com/http://www.zebraimaging.com/products/3D-Holographic-PrintsThis is the supposed holographic display:
http://www.zebraimaging.com/products/motion-displaysThe research paper showing how the device actually works is linked on the site too, I think. Some really hardcore physics in there.
Edit again: I forgot to mention, that the Hololens is a self contained unit, totally untethered and battery powered. No idea on battery life yet.
As are many others, e.g. all those "strap a smarphone to your face" HMDs. On the other hand, that feature comes with an enormous price, because having the computer embedded in the device will seriously hamper the amount of graphical and tracking work you can do if you use a low spec, battery sipping CPU or the battery will be flat in no time if you go with a high perf. CPU. My suspicion is very much the later - they most likely used the same or very similar hw as they are using in the Surface tablets, i.e. an X86 CPU and those are not known for long battery life. Also streaming content over wireless is pretty much a no go because of the bandwidth and low latency required to feed the high resolution displays used in these devices.
BTW, the classic way of creating a volumetric (that is the correct term for the "floating" 3D imagery, not "hologram") projection is using a rotating screen. E.g. this device:
Explanation is here:
http://www.infovis.net/printMag.php?num=88&lang=2Probably the first one of this type was the Cathode Ray Sphere by B.G. Blundell:
That's 1994, folks. No fancy data projectors there, good old vacuum tube CRT technology! I have actually met Dr. Blundell at that time, he presented his design of this gizmo at a conference I attended as a student. It was really fascinating device.