Comment by rsp1984 | Hacker News Reader

Comment by rsp1984 | Hacker News Reader

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This is not a "true" LiDAR in the classical sense (where you send out a laser beam and measure time passed until return). It's rather an indirect ToF sensor that uses modulated light bursts that flood the entire scene.

This approach typically works well for close-range convex surfaces (hand tracking, bin picking, face ID) but fails pretty miserably when longer ranges and concave surfaces are involved, due to quadratic signal dropoff and multipath errors.

As far as I understand, what the team has achieved is lowering the power requirements for the modulation part. It means they can spend the saved power on making the modulated light brighter, which should give them a bit more range. I haven't seen any other major improvements though and none of the other issues with iToF were addressed.

Not trying to downplay the achievement, just saying it is still affected by the usual tradeoffs and probably just occupies another niche in the high dimensional space of 3D cameras, rather than spanning many of today's niches.

This approach typically works well for close-range convex surfaces (hand tracking, bin picking, face ID) but fails pretty miserably when longer ranges and concave surfaces are involved, due to quadratic signal dropoff and multipath errors.

Exactly. This has been used before for short-range sensors, modulating the outgoing light electrically. Microsoft used it in the second generation Kinect. Mesa Imaging used it in 2013.[1] The prototype of that was shown in 2003.[2] I looked into this in my DARPA Grand Challenge days.

Since it's a continuous emission system, you need enough continuous light to overpower other light sources. Filters can narrow the bandwidth, so you only have to be brighter at a specific color. This works badly outdoors. Pulsed LIDARs outshine the sun at a specific color for a nanosecond, and thus can be used in bright sunlight. Also, they tend not to interfere with each other, because they're receiving for maybe 1000ns every 10ms, or 0.01% of the time. A little random timing jitter on transmit can prevent repeated interference from a similar unit.

So, short range use only. For more range, you have to use short pulses.

For short range, there's another cheap approach - project a pattern of random dots and triangulate. That was used in the first generation Kinect and is used in Apple's TrueDepth phone camera.

[1] https://www.robotshop.com/community/blog/show/mesa-imagings-...

[2] https://www.researchgate.net/publication/228602757_An_all-so...

Interesting bits about pulsed LiDAR. Is there any camera available to buy on the market that uses this technology?

iPhone/iPad's LiDAR Scanner.

This is not directly my field, but in general I've found that many, many articles (and not just free-daily-rags, but also from reputable magazines and news sites) always seem to inflate every scientific achievement, where some minor discovery (still worth a published article) is presented as "new cure for cancer found!", and even worse if some well-known substance is used (eg. caffeine makes medicine delivery faster), the title would say "coffee cures cancer!".

And not just medicine... just look at the number of "new, 10.000x better battery discovered" articles posted here.

Flashier headlines get the clicks which means $$$

I'm curious since you know your stuff. Is structured light a form of modulated light?

Nope. Structured light is projecting a geometric pattern into the scene and viewing it from from a camera that's offset by some amount vs. the projector. The original Kinect works this way.

Structured light is modulated in space rather than time. Accordingly, distance is inferred from offset in space (pixel, ie. angle) rather than time (phase).

I would have assumed they'd choose to work in a nice narrow absorption band like the 5.6u CO2 where solar illuminance is almost blocked. I know they commonly do that with structured light. It does add cost for filters and I don't know how well these ToF or standard CMOS imagers work there.

https://www.researchgate.net/publication/328024940/figure/fi...

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