Comment by mhalle | Hacker News Reader

Comment by mhalle | Hacker News Reader

This device is a volumetric display, similar in product placement (if not exactly the same illumination technology) to the volumetric dome display from Actuality Systems about 20 years ago.

Volumetric displays have their place, but they can't display general occlusion of far objects by near objects. That restricts their application to non-photorealistic scenes that often look like clouds of points.

Since occlusion is one of our strongest depth senses (much stronger than stereopsis), that's a significant restriction.

Big spinny things are also hard to scale.

While other autostereoscopic display technologies like the parallax barrier displays from Looking Glass Factory give up the ability to walk around the scene, they work with no moving parts and can display photorealistic scenes (either synthetic or photographic).

Again, different display technologies have their place, but volumetric displays have historically struggled to compete in the 3D display market.

So, they show mostly correct applications: CAD / 3D-modeling work, schematic visualizations, etc.

Also, for an individual seated user, it's relatively easy to adjust the direction of gaze, and do occlusion at the rendering level, giving a rough idea of occlusion. They even show it in one of the segments of the video on the product page (with some color balls).

Sure, it's possible to approximate occlusion for a fixed viewer. At that point, though, the display is competing with displays like looking glass (lenticular, parallax barrier, or stereograms) that are higher resolution, cheaper, and have a rendering pipeline that's more compatible with standard computer graphics.

Occlusion could be done with head tracking for one observer (not both eyes though); but defeats the point. I'm guessing AR glasses will work for much of this.

About “can't display general occlusion”, wikipedia calls this a misconception. But it does later state that it requires sacrificing vertical parallax.

> It is often claimed that volumetric displays are incapable of reconstructing scenes with viewer-position-dependent effects, such as occlusion and opacity. This is a misconception; a display whose voxels have non-isotropic radiation profiles are indeed able to depict position-dependent effects.

> the ability to reconstruct scenes with occlusion and other position-dependent effects have been at the expense of vertical parallax, in that the 3D scene appears distorted if viewed from locations other than those the scene was generated for.

https://en.m.wikipedia.org/wiki/Volumetric_display

> This is a misconception; a display whose voxels have non-isotropic radiation profiles are indeed able to depict position-dependent effects.

Sure, if you replace each pixel with a tiny light field display pixel you can do occlusion.

Unfortunately, that's a big challenge for a volumetric display, particularly a spinning one. There's a mass problem (heavier spinny things are more difficult than lightweight spinny things). There's also a wire problem if the elements on the spinning element are active and need to be addressed, since the wires generally need to come through the hub. If a projector is used and the spinning element is passive, then there's a tricky alignment issue.

And in any case, there's a bandwidth issue, since every 3d point is now addressed by a 1D or 2D array. That's an enormous amount of the data that ultimately needs to be uncompressed by the time it hits the display hardware.

A hogel volume can be reduced into a 1bpp 2d plane representing the interference problem. Literally, a hologram. Probably the computational effort to do this in realtime is within reach of current GPUs.

"non-isotropic radiation profiles" is probably better expressed as the ability to produce light that can be modulated differently in different directions. That's what's required to show proper view dependent shading on a surface, and what's required to turn off a voxel that's behind another voxel from a particular view angle.

That's arguably a different class of display, and an extremely complex one.

To build it you'd likely want to sacrifice vertical parallax (to allow the use of a spinning lenticular sheet or something else, and to reduce the information capacity required), but there's no fundamental reason that prevents a full parallax display of this type (a spinning integral photograph).

From an engineering complexity point of view, it's the hardest of all worlds.

> Big spinny things are also hard to scale.

I worked for people that were making these kinds of things (in 2009-10[0]) for advertising (8ft high, 6ft diameter spinning cylinder[1]; 8ft high, 4ft wide flat display with 8 interconnected spinning discs) and yeah, they were absolutely terrifying. Especially the flat display - sounded like a jet taking off when starting up and wasn't much quieter at full pelt[2].

[0] I suspect these things are easier now with lower power LEDS, etc. given you can cover a cylinder in directly addressable LEDs pretty cheaply and don't need the massive spinning death machine.

[1] Deployed at a few places around the UK but now sadly removed.

[2] They were intended for roadside displays, not shopping malls.

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