Comment by scarmig | Hacker News Reader

Comment by scarmig | Hacker News Reader

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I wonder how hard it would be to scan ingested maps for interesting submerged structures, and also roughly how many cars would turn up if it's feasible. I'd guess... O(100)?

I can't find a link to the story at the moment (I'm on mobile), but I read recently they've started doing just that - doing image analyses on aerial/sat map data - to find cars and other things submerged in the Bayous here in Houston. Previously [1] they used more on-site resources, such as sonar, drones, and people in kayaks; etc.

1: https://www.houstonchronicle.com/local/gray-matters/article/...

I found a skateboard in a smaller bayou this past weekend in fairly good condition. I can’t imagine what else is down there. There is also a very surprising amount of fish in the bayous, including loads of plecos (aquarium sucker fish).

You might enjoy magnet fishing!

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

Never heard of that! I can’t imagine how many weapons one would find at the bottom of the Houston bayous.

also r/magnetfishing

Hate to be that nitpicky guy but O(100) isn't a thing. You'd write O(1) or O(N), O(N^2) etc.

While not technically correct the meaning is clear enough and commonly used as shorthand for "on the order of"

I thought O(1) = O(100) so it would still technically be correct, no?

It would be technically correct if what he meant was that the problem would be solved in constant time.

I bet it wasn't.

Edit: O(1) technically is O(100) but that's probably not what they meant.

That is the sort of pedantry up with which I will not put. From the definition of big-oh, the choice of the number one is completely arbitrary.

> From the definition of big-oh, the choice of the number one is completely arbitrary.

is it? not up on the formal theory, but:

O(n) -> on the order of n x 1 time intervals of processing

O(n)^2 -> on the order of n x n time intervals of processing

etc.

so if there is a single fixed interval, N is irrelevant, leaving you with 1, denoting the single fixed interval

f(x) is O(1) means that there exists x0, M > 0 such that for all x > x0, |f(x)| <= M. Clearly, the statement still holds (for different M) if 1 is replaced by any positive number.

https://en.wikipedia.org/wiki/Big_O_notation

You wouldn't last long among the product managers at my company. Everything in all their docs and slides is O(3 weeks) or O(4 eng).

That'd drive me mental. Especially when there is c. or ~ for that job.

“We’ve received the O(pizzas); they’re in the kitchen.”

I wonder if there's anyone scanning satellite imagery for the word "HELP", or if we should agree on some other symbol people could use to ask for help that would be easier to discover with computer vision and wouldn't be English-specific.

How large should you make the letters? Satellite resolutions range from 2m for Planet Labs, 50cm for Geoeye to ~10cm for that spy satellite Trump leaked recently. The MNIST dataset of hand written digits uses 28*28 pixels, but you can get away with less. Maybe 50 meter by 50 meter letters?

If you know binary you could also include extra information by using rows of 5 squares ~1m in diameter.

How frequently do we refresh our coverage of imagery of planet earth?

Some sort of universal symbol could be great. Especially if you knew that within X days there was a strong chance it would be spotted and rescue folks alerted.

Planet Labs images all land once a day at 3m-5m resolution and will sell you the data. At least that's their goal/pitch and they get reasonably close

https://nbremer.github.io/planet-globe/

What a beautiful use of human intelligence.

I can’t imagine getting the entire world to learn a new symbol for “help” on the off chance someone needs to signal to passing satellites. Also, I believe SOS is fairly well-known.

How about "bigger than a sedan at the bottom of a pond"?

Google Maps uses aerial imagery (photos taken from planes)[0] because it's higher resolution, and I bet that's what you're seeing here. They don't fly those planes often and they don't fly them over random uninhabited islands, whereas there's a company that takes satellite images of all the land on the planet daily.

[0] https://support.google.com/earth/answer/6327779?hl=en

Id be relatively surprised that this isn't already a thing.

Interesting thought but uneducated guess.

I bet IR scans could help, similar to how they are discovering ancient cities buried deep in the jungle.

Space-based radar is also available which provides views of metal content as an intelligence product. Brighter parts of the image = more metal. I'm not sure if it's commercially available but it would sure help to find cars in shallow water...

There is a lot of other metal in shallow water though. Just think about rubbish, buoys, marker posts for utilities, boats, sewer outfalls, gratings etc.

Presumably Google, or their contractee, are scanning with other frequency ranges (IR, UV) when they do visual photography for Google Maps.

So any companies make this kind of imagery data available free; I'd be interested to see some.

I meant uneducated in reference to his guess of O(100). That makes no sense.

Worldview 2 has a band that is specifically intended for shallow water.

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