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Comment by thewebguyd | Hacker News Reader

I don't think there's a good solution right now. You can't just go based on surrounding traffic because humans are also stupid and flood their cars all the time.

You could maybe use short-wave infrared cameras combined with ground penetrating radar, but it'll get real expensive so probably not commercially viable.

I think the only "good" solution is to have the car be overly paranoid, and if it detects water on the roadway that's bigger than some arbitrary diameter (to rule out mud puddles), then the car has to assume its a flood, stop, and escalate to a human or change the route.

Alternatively, just don't run Waymo operations during flood/flash flood warnings. Maybe we as a society need to top forcing everything to still operate normally during natural disasters. It's OK to shut things down when safety calls for it, and that applies to human drivers too. If areas are flooding, stay home.

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> Alternatively, just don't run Waymo operations during flood/flash flood warnings.

FTA

> the company said that it shipped an update to its fleet that placed “restrictions at times and in locations where there is an elevated risk of encountering a flooded, higher-speed roadway,”

> But even those precautions apparently were not enough to stop the Waymo robotaxi from entering the flooded intersection in Atlanta. Waymo told TechCrunch on Thursday that the storm in Atlanta produced so much rainfall that flooding was happening before the National Weather Service had issued a flash flood warning, watch, or advisory.

Their fleet is constantly scanning the area with lidar, which is assembled into maps. If those maps are in 3d rather than a 2d road grid you can calculate puddles very accurately with no extra sensors:

- Find the edge of the water using vision or lidar

- look up the ground height at that position in your map data. That is the water level

- run a flood fill of the local 3d map starting from that point, with that water level. That gives you an exact shape of the puddle

- for any point on your planned path, you can now check if the point is in the puddle (per the flood fill above) and how deep the water is (difference between puddle's water level and ground height)

- use that either as a go/no-go for a planned path, or even feed this into your pathfinding to find a path with acceptable water level

The main limitation is that it assumes that the ground hasn't changed. It won't help in a landslide, or on muddy ground where other cars have disturbed the ground. But for the classic case of the flooded underpass or flooded dip in the road it should be very accurate

The vehicles have enough information to make the determination. Ground data is available in the point cloud and usually labeled as such. Water sometimes shows up in point clouds, sometimes it doesn't depending on conditions and wavelength.

If the apparent road surface is higher than the mapped ground surface, probably a puddle. If your point cloud has a big hole, also probably a puddle.

This assumes you aren't doing ground plane removal, of course. But it's quite likely that Waymo is using a heavily ML approach these days, and I can imagine the poor thing getting very confused if it's not an explicit training goal.

Do you how often you get flash warnings in Atlanta? And local roads flood far more often than flash food warnings are issued.

If you can’t handle this issue, you really can’t operate in Atlanta.

Would be interesting if you can compare the surface roughness of pavement vs. the surface of water, wind would disturb it too

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