
Under the Hood of Luminar's Long-Reach Lidar - sohkamyung
http://spectrum.ieee.org/cars-that-think/transportation/self-driving/under-the-hood-of-luminars-long-reach-lidar
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bcatanzaro
The article says Luminar's advantage comes largely from wavelength: the longer
wavelength they use is absorbed more strongly by water, meaning it won't
penetrate to the retina, even at higher power, which allows them to have much
better range and resolution.

But what about the weather? The atmosphere often contains water. Does anyone
know Luminar's performance in fog or rain?

I'm always worried self-driving cars will be set back by having so much of
their development take place in sunny California.

~~~
Symmetry
Luminar's lidar beams will be absorbed by water rather than scattered so fog
will effectively seem black to it rather than white and it will be just as
unable to see through rain or fog as normal lidar or your eye.

Thankfully if it's going to be developed in SF they'll be getting a lot of
experience with fog.

~~~
dweekly
True. For details on relative absorption and scattering and performance on
rangefinding at 905nm vs 1550nm see
[https://www.degruyter.com/downloadpdf/j/oere.2014.22.issue-3...](https://www.degruyter.com/downloadpdf/j/oere.2014.22.issue-3/s11772-014-0190-2/s11772-014-0190-2.pdf)

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Animats
200m for a mechanically scanned LIDAR isn't a big deal. There are older flash
LIDARs that can reach 400m with a 9 degree field of view.[1] Flash LIDARs have
a field of view vs. range tradeoff, since they illuminate the entire field of
view at one time. Range gated imagers, another form of flash LIDAR, have
ranges out to kilometers.[2] (Those guys are using a lot of power, but it's
spread over a wide area.)

The eye safety problem can be overcome by making the outgoing beam bigger.
What matters is how much energy comes through a hole about 1/4" in diameter,
the size of the pupil of the human eye. If you enlarge the outgoing beam, by
running it through a collimator backwards, the energy per unit area decreases.
Expand a beam to a 2" circle and you have reduced the power per unit area by
about 50. The risk is to someone coming up to the thing and staring into the
beam, not out at range where energy per unit area is much lower.

Cost remains a bigger issue than range. Give it 2-3 years.

[1] [http://www.advancedscientificconcepts.com/products/older-
pro...](http://www.advancedscientificconcepts.com/products/older-
products/tigereye.html) [2]
[https://www.youtube.com/channel/UCLrAizlR4ry9Nu6A7BXBBdg](https://www.youtube.com/channel/UCLrAizlR4ry9Nu6A7BXBBdg)

~~~
jacquesm
Are there any cumulative effects regarding eye safety?

As in: if 100's of cars in your field of view, say a traffic jam in the
opposing lane are all firing LIDAR would it add up to trouble?

~~~
diggernet
Excellent question. I foresee a booming market in lidar-blocking sunglasses.

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ianai
Why use lasers at all? My brain doesn't need anything like a laser to figure
out where objects are in relation to me. Is there something about a human eye
that a camera can't reproduce for a machine?

~~~
diggernet
Yes. The human eye is attached to the human brain, which we haven't yet been
able to reproduce for the machine.

~~~
JumpCrisscross
> _the human eye is attached to the human brain_

And those human brains are attached to human arms which navigate Americans
into 32,000 motor vehicle deaths a year [1].

[1]
[https://en.wikipedia.org/wiki/List_of_motor_vehicle_deaths_i...](https://en.wikipedia.org/wiki/List_of_motor_vehicle_deaths_in_U.S._by_year)

~~~
diggernet
Sure, but that's not what ianai asked. The question was what makes an eye
better than a camera. You are comparing the human brain to a hypothetical
future ideal machine brain. Replace every single driver on the road today with
current state of the art machine brains operating under exactly the same
conditions, and that 32k death toll will look good in comparison.

~~~
JumpCrisscross
OP asked why we need more sophisticated hardware for self-driving cars than
human drivers possess. My response is that the _status quo_ is not good enough
for an emerging technology. Self-driving cars are not politically viable if
they kill a hundred people a day. They may not be viable if they kill 1/10th
that number. That's why we need better sensors for them than we possess.

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deegles
How do Lidar devices deal with potentially dozens of other Lidars operating in
the same area?

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mozumder
You can have all the sensor-tech in the world, but self-driving cars aren't
going to take off until you have standardized car-to-car communications and
smart roadways designed for self-driving cars, such as pre-mapped lanes and
surfaces as well as smart roads communicating road-condition and obstruction
information.

~~~
Animats
Car-to-car communications are not necessary for automatic driving. They may
even be undesirable, as a potential source of bad info. Google/Waymo doesn't
need them. They make the point that there are lots of things in the
environment, from bicyclists to moose, that aren't going to cooperate with the
system.

The need for super-detailed maps is probably temporary. A reasonable goal is
to have the ability to drive anything with a basic map (Google StreetView
level) at slow speed, then retain info to do it again at faster speed. Some of
that mapping info may later be uploaded for use by others.

~~~
diggernet
I really hope they get self driving cars working with nothing more than
current GPS maps, plus lots of sensors. Considering the drive I took this
weekend, past actively changing construction zones, landslides, along
infrequently traveled roads (and even a logging road), I wouldn't want to
trust my life to stale data.

~~~
amatic
I'd love to see self-riding multileg robots, like an advanced version of
Boston Dynamics alpha dog. You don't even need roads for them. With some kind
of super-stability they could become more comfortable than vehicles. Perhaps
we'll have human carying drones a bit soner, though. Still, in a bit more
distant future, roads might become obsolete.

~~~
Animats
It's been tried a few times. Early versions were really clunky. Later versions
were usually art projects.

* General Electric Walking Truck (1969) [1]

* Adaptive Suspension Vehicle (1984) [2]

* Korean giant mecha (2016) [3]

The BPG Motors Uno transforming motorcycle seemed a good idea, but they gave
up on it.[4]

[1]
[https://www.youtube.com/watch?v=ZMGCFLEYakM](https://www.youtube.com/watch?v=ZMGCFLEYakM)
[2]
[https://www.youtube.com/watch?v=DIiD1JimBXQ&feature=youtu.be...](https://www.youtube.com/watch?v=DIiD1JimBXQ&feature=youtu.be&t=25)
[3]
[https://www.youtube.com/watch?v=bqZWNn5qZ7U](https://www.youtube.com/watch?v=bqZWNn5qZ7U)
[4]
[https://www.youtube.com/watch?v=odI4WaYEcCU](https://www.youtube.com/watch?v=odI4WaYEcCU)

