Transform Cellphones Into a CCTV Swarm

holy_calamity writes "Swiss researchers have developed java software that has bluetooth-capable camera phones form a distributed camera network. Each phone shares information on visual events with its neighbours and can work out the spatial position of phones around it (pdf). The software will become open source sometime next year, and the creators say it could be used to make a quick and dirty surveillance system. 'The phones currently use the average speed people walk to guess the distances between themselves, based on how long people take to move from one phone's view to another's. In testing, the system determined the distances between each phone with about 95% accuracy. They were placed 4 metres apart, making it accurate to about 20 centimetres. In future, recording the speed at which objects pass by would make more accurate judgments possible.'"

Comments

So...

[Smordnys s'regrepsA]

...now stalking my favorite celebrity can be a group event!

Holy privacy violations Batman!

[edunbar93]

it could be used to make a quick and dirty surveillance system

Emphasis on "dirty". People take those things into their homes and leave them on their bedroom end-tables you know.

The real question at hand here.

[blhack]

But does it run skullbocks?

F&TF3: Tokyo Drift

[OctoberSky]

Is this basically the last drive sequence of F&TF3: Tokyo Drift?

Where all the kids are viewing/filming the race down the mountain as it goes by?

I thought that technology (well, that CGI) was rediculous but maybe it's not that far away?

(NOTE: Give me Karma, I admitted to watching that movie, that's gotta count for something).

I predict

[Buelldozer]

That the police are going to really dislike this.

concert-recording on the cheap

[smellsofbikes]

I've spent some time designing and programming (but will never finish) something similar to this, just using cellphones' audio capabilities. Imagine getting twenty random people at a concert to call into a server and leave their cellphones running, recording the concert from twenty different points. From the overall stream, you should be able to derive an excellent, local-noise-removed bootleg, and from a bit of playing with signal intensities you should be able to figure out where the individual recorders were and do some nice sound balancing.

We're all carrying these great little computers: we should start doing networked or collaborative stuff with them.

Re:concert-recording on the cheap

[Jherek Carnelian]

This might be true with a 44- or 48kHz sampling rate, but "phone quality" 8kHz sampling will give you something that sounds worse than a cassette recorder stuck inside a coffee can. Not so fast there. If it is possible to algorithmically combine a handful of low-resolution (i.e. low sample rate) images of the same scene to get a high resolution version, it ought to be possible to algorithmically combine a handful of low-resolution recordings of the same audio to get a high resolution version.

Re:concert-recording on the cheap

[Anonymous Coward]

If it is possible to [apples], it ought to be possible to [oranges].

Sorry, but speaking as someone with a degree in electrical engineering who spent the better part of a decade studying this stuff, it just doesn't work like that. You can use padding tricks increase the [false] resolution of the spectrum you're dealing with, but you can't recover signal that you failed to record in the first place. See also: Nyquist-Shannon sampling theorem.

For a simpler analogy, it's like using 16-bit registers to record 32 bit integers. No matter how many 16 bit registers you use or how you combine them, you're not going to recover the upper 16 bits -- they're lost because you didn't record them.

Re:concert-recording on the cheap

[matfud]

Yes that true, but only for one source. If you have multiple 8khz signals whose sample points are not synchronized then you can combine them to improve the overall frequency range obtainable. However this would increase the final achivable frequency in proportion to the log of the number of sampling devices (under ideal situations) so you would need a fair few sources (If I remeber correctly). Mobile phones would probably be quite far from this ideal as they
a) would be physically seperated so you'd have to perform some correlation first to remove the arbitrary time delays from the audio source to the phones and this would remove some of the resolution
b) would not be sampling at the optimum times wrt each other (perfectly interleaved sampling).

A similar techique is used for images. An 8 bit camera can record, at best, 256 levels of grey. If you take multiple images of the same scene and average them together you can increase the effective number of grey levels you can reconstruct while also removing the effects of thermal noise. Doing similar with audio would not use averaging but would instead interleave the samples from the out of synch microphone ADC's.

matfud

Re:concert-recording on the cheap

[evanbd]

The problem with this approach is that audio ADCs have an analog antialiasing filter in front of them. It's not just that you can't see the high frequencies because you don't have enough samples; they're actually *removed* from the analog signal before it's digitized. If they weren't, you could recover them with enough microphones, but you'd also get weird aliasing artifacts. As it is, they're gone, never to return.

Re:concert-recording on the cheap

[fenodyree]

That comparison is flawed.
To use a car analogy: You can construct a complete working car from a junkyard provided that the cars in the junkyard have different problems and conversely different working parts.
As the way multiple low resolution images of the same seen create a higher resolution is primarily based upon the (usually accurate) assumption that the images will be lit differently such that where information is lacking in one image, it _is_ in another, and vise versa.

However, with the phones, the same set of frequencies (3,400 Hz) and going to be dropped by bandpass filtering.

Re:Open source surveillance

[jibster]

Maybe the glass is half full.

Think of a peaceful protest group using, an admittedly far superior, form of this to camera swarm the police. The perpetrator of any action, a policeman clubbing an innocent citizen for instance, might question their actions if they knew they were surrounded by this swarm.

Re:Open source surveillance

[fm6]

Or even worse, mandatory!

The team also found that ...

[Van Cutter Romney]

The Swiss team also found a unique characteristic of the network that it used to swarm around one of the nodes more often than not. Later they pinned it on the only hot blonde in the team.

Huh ?

[ant-1]

A CCTV system from BT cellphones ? Why, oh why ? Because boffins have time and my money to lose ?
Somebody please explain the use of such a... discovery ?

Ah.

Surveillance.
I get it now. The T word is about to be spoken, again. Great. I'm looking forward to BT-holding surveillance militia roaming the streets.

Analyze the average quantity of pocket lint?

[kevmatic]

Most people I know don't keep their cell phones in some snap-off carrier on their belt like a modern-geek pocket protector. They stay in pockets, where they can't see. And women keep them in purses. So only a few phones are actually going to be able to see without their owners holding them out on purpose.

What's the point of this, again?

Can you see me now?

[r_jensen11]

Good!

Re:Open source surveillance

[VE3MTM]

There's a name for this: it's called "Sousveillance".

Closed-circuit?

[jpfed]

Correct me if I'm wrong, but doesn't CCTV mean "closed-circuit television"? As in, the camera is connected with a solid conductor to the display? If that's the case, then wouldn't a system that transmitted video over the air (at least, without displaying it locally first) be something other than CCTV?