That's a reasonable basic overview.

I'm surprised that rotating scanners are still used. It's been twenty years since Velodyne built their first one. They work OK, but cost too much. I was expecting flash LIDAR or MEMS mirrors to take over. Continental, the auto parts company, bought the leading flash LIDAR company over a decade ago, but the volume market a big parts company needs never appeared.

Waymo is still using rotating LIDARs even for the little ones at the vehicle corners. Those need less range. There needs to be a cheap, flush-mounted replacement for those things. The location is too vulnerable. Maybe millimeter phased array radar mounted behind Fiberglas body panels. Waymo needs to solve that problem before they do New York.

The LIDAR on top may not be a problem. Insisting that it has to go away to "look like a car" is like insisting that cars had to have the form factor of horse-propelled buggies. Early cars looked like buggies, but that didn't last.

One big advantage of pulsed LIDAR over continuous is that the interference problem between identical units is much less. The duty cycle is tiny. Data from one pulse round trip is collected in less than a microsecond. Just put some randomization in the pulse timing and getting multiple conflicts in a row goes away.

> I'm surprised that rotating scanners are still used. It's been twenty years since Velodyne built their first one.

They're even older than that. SICK have been pointing laser range finders into spinning mirrors since about 1995 - albeit mostly for industrial safety systems which can be quite price-insensitive.

There's a few things to know about LIDAR to understand why spinning lasers make sense.

First of all, anything emitting a cone of light encounters "inverse square dropoff" - where moving twice as far away means you get a quarter of the light, per unit area. This is most visible with flash photography at night - but it also applies to LIDARs. And in an automotive application, ideally you want to be able to sense things 100m away. Illuminating a laser spot is much more practical than illuminating everything.

Secondly, whatever light source you use has to be eye-safe. And sure, IR has safety advantages over visible light here - but a light source bright enough to illuminate things at a 100m distance would be very hard to make safe, even with the advantages of IR. As a scanning laser never lingers in one point for long, it can safely be much more intense.

The third thing to know is whatever light source you're using, you're in competition with the sun. Sometimes the sun is low in the sky and directly dazzling your sensors. Other times it's illuminating the same things you want to illuminate. This means you can't make up for a weak light source and inverse-square dropoff with clever signal processing.

And finally, the makers of these cars envisage a future where every single vehicle on the road is using this technology. So there's also a risk of the reflected returns of two different vehicles interfering with one another. Even rotating LIDAR can be vulnerable to it, but flash LIDAR is particularly vulnerable.

Meanwhile, automotive companies aren't scared of moving parts. A car has loads of spinning parts already; they have mastered the art of making spinning things that can keep spinning for thousands of hours.

Waymo have in house radar, I think in the 70GHz gap in the absorption spectrum. They're pretty obvious as sort of paperback book sized planes, mounted near other sensors IIRC.

The old Velodyne units were actually susceptible to damage if you left two units running right next to each other. I did hear a proposal at some point for a different but similar unit to use GPS time to sync the rotations of all the units we had live so they wouldn't be pointed at each other, but in practice it seemed to not be a huge issue.

BTW I once gave you guff about continuing to bring up Conti's flash LIDAR, and in retrospect I wish I hadn't, I really enjoy your contributions here.

The SNR for flash Lidar is really low because you spread the beam out over such a large area.

Most automotive Lidar already operate in a “photon starved regime”, ~200-300 photons per return[0]. If you spread that over the entire scene, your snr drops quickly.

This forces you into 1550nm, and a large detector array and high power laser at 1550nm is extremely expensive.

As for MEMS, it’s been a while but I think FOV/steering angle range , steering speed and even maximum beam power were concerns

EDIT: my Lidar friend Jake reminded me that the appetizer size is also an issue with MEMS- smaller aperture = less light collected = lower SNR

[0] https://www.hamamatsu.com/content/dam/hamamatsu-photonics/si...

Continental is folding their automotive LiDAR division and is laying off everybody.

> They work OK, but cost too much.

Costs have dropped dramatically in the past 20 years and continue to do so.

> There needs to be a cheap, flush-mounted replacement for those things.

Why? Corners are the optimal mounting position for maximum visibility. It allows the car to -in-effect- see around corners in ways no centrally mounted sensor can.

> Waymo needs to solve that problem before they do New York.

What? Because of vandalism?