Part of my job is to review security footage for reported incidents.
If there is a long-lasting visual cue that the event has or has not happened yet (e.g. a window is either broken or not), then a binary search is very useful.
If the event lasts only a moment and leaves no visual cue (e.g. an assault), then binary search is practically useless.
If the event lasts only a moment and leaves no visual cue (e.g. an assault), then binary search is practically useless.
But you will see the event happen though.
It’s a matter of if you can identify who the perpetrator is or not, but at least that due diligence should be done by police, looking at the person doing the crime and see if they can be identified.
Let’s use the example of a bike theft. We enter into evidence a 4-hour security cam video that shows the thief with the bike.
Scenario A: The camera can directly see the bike rack, and the bike in question is visible at the beginning of the video, and not visible at the end. Somewhere in this 4-hour video, someone walks up to the bike and takes it out of the bike rack. You can use a binary search to find the moment that happens in this video because you can pick a frame and say “Ah, this was before the theft; the bike is still there” or “ah, this was after the theft; the bike is gone.”
Scenario B: The camera can’t directly see the bike rack, but can see the doorway you have to walk through to get to the bike rack. So somewhere in 4 hours of doorway footage, someone walks through the door, then a short time later walks back through the door with the bike. A binary search won’t help here because the door looks the same at the beginning or end of the video. A simple binary search won’t work here because the door looks the same before and after.
Scenario B: The camera can’t directly see the bike rack, but can see the doorway you have to walk through to get to the bike rack. So somewhere in 4 hours of doorway footage, someone walks through the door, then a short time later walks back through the door with the bike. A binary search won’t help here
I never said it works 100% of the time. This that it would work most of the time. And I make that statement based on the fact that usually the environment changes around the event, or the event happens long enough to be detectable, if not by humans, then by AI.
In all of my comments I’m assuming that that focal point of the crime is visible.
But even if it wasn’t, if the person stealing the bike knocks over a trash can while doing it and that’s in the camera view it would still be useable. Or if a crowd congregates around the focus point and looks around for the bike, that would also make a binary search feasible.
That’s always just been my point, that a binary surgery more often than not works because most times the environment around the event changes in some way, from subtle to extreme.
You would have to be confident that said change in environment was done by the bike thief. What if that knocked over trash can was done by some unrelated bored teenager twenty minutes after the bike was stolen?
It might be better to use some software to remove any frame of video that is identical to the one before it, no motion is taking place, etc. then manually watch the much shorter video of “only when stuff happens.”
You would have to be confident that said change in environment was done by the bike thief.
Well, the change would happen, the human will be noticed, and then they can watch that moment in time on the tape to see who did it. The binary search would be about shortening what portions of the video tape a human/AI would have to review manually.
It might be better to use some software to remove any frame of video that is identical to the one before it, no motion is taking place, etc. then manually watch the much shorter video of “only when stuff happens.”
So, I hope you’re not under the impression that I’m advocating binary search as the ONLY way of doing a search. I’m just staying within the confines of the subject as brought up by the OP, which was about binary searches.
At the end of the day its about detecting the change/aftereffect, and not the search inandof itself. A binary search just helps you narrow down the video you have to watch manually, especially when there’s allot of it to review.
This is the explanation that CosmicCleric needs in order to understand binary search.
Because as it is, (s)he’s failing abysmally at demonstrating any understanding whatsoever of that subject.
I’ve written binary searches before.
But you will see the event happen though.
Not with a binary search.
Edit: just collapse this thread and move on. Cosmic Cleric is an obvious troll.
But you will see the event happen though.
Not with a binary search.
Yes you will.
A binary search is just what it says, it’s just for searching only.
When you find that moment in time where the bike was there one moment, and then the next moment the bike’s not there, then you view at regular or even slow-mo at those few seconds of the bike in the middle of disappearing, and see the perpetrator, and hopefully can identify them.
You didn’t get what was talked about here. Re-read the topmost parent comment.
How do you binary search for two people arriving, one punches the other, they both leave?
How do you binary search for two people arriving, one punches the other, they both leave?
In the same way the OP talks about it …
You don’t watch the whole thing, he said. You use a binary search. You fast forward to halfway, see if the bike is there and, if it is, zoom to three quarters of the way through. But if it wasn’t there at the halfway mark, you rewind to a quarter of the way though. Its very quick. In fact, he had pointed out, if the CCTV footage stretched back to the dawn of humanity it would probably have taken an hour to find the moment of theft.
Instead of a bike, you look for the aftereffects of a fight happening (chairs knocked down, tables turned over, etc.). You can even look at how many people congregate around the location of the fight before and after the video as a ‘marker’ to the point of time the fight was happening/just finished.
Edit: One thing we didn’t even mention, AI can also be used these days to notice subtle changes in the video. If a video is a static image of an alley, then two people walk in the alley and fight, even though they leave no traces behind, that moment of the fight is caught on the video with activity/movement. Motion sensor movement, basically.
Your adding things that would allow a binary search work, but the question was in a situation where the only evidence is the conflict itself
2 guys enter one guy punches the other guy they both leave. Nothing is moved no blood was created,
you could not use a binary search effectively to duduce when it occurred.
Your adding things that would allow a binary search work, but the question was in a situation where the only evidence is the conflict itself
I’m describing the vast majority of fights that happen in the public. Also, you’re trying to move the goalposts by focusing on a fight, when the discussion is about the theft of a bike.
Edit: One thing we didn’t even mention, AI can also be used these days to notice subtle changes in the video. If a video is a static image of an alley, then two people walk in the alley and fight, even though they leave no traces behind, that moment of the fight is caught on the video with activity/movement. Motion sensor movement, basically.
You are seriously confused. OP specifically said that you’re fucked if there is no visual cue.
You are seriously confused.
And you are seriously trying to kill the messenger.
OP specifically said that you’re fucked if there is no visual cue.
And I’m saying there’s ALWAYS a visual clue/cue, always. Either the bike is there one minute and gone another, or a fight breaks out and trashes the place from the fight. In the vast amount of cases, there’s always a visual difference.
And in this case we’re talking specifically about a bike, going missing.
You didn’t get what was talked about here. Re-read the topmost parent comment.
I was responding to this …
Part of my job is to review security footage for reported incidents.
If there is a long-lasting visual cue that the event has or has not happened yet (e.g. a window is either broken or not), then a binary search is very useful.
If the event lasts only a moment and leaves no visual cue (e.g. an assault), then binary search is practically useless.
I disagree with the “leaves no visual cue” part, as I’ve commented on. There’s ALWAYS something caught on the video to help determine things. Maybe not enough, but never nothing.
Maybe I’m not understanding both arguments here but I’d like to understand. I’ve had to review footage of a vending machine being shaken to release drinks.
You have no before or after visual clue as to when the event took place. The only indication is when you physically see it happening. The same could be said for an assault. If nothing is changed in the before or after static still how can you pinpoint the incident?
You have no before or after visual clue as to when the event took place.
That wouldn’t necessarily be true. If you shook it hard enough to move the contents inside the vending machine and the vending machine had a glass front then you would have a static change that would last from the time the event happened until a human being came to work on the machine. That change would be detectable.
Or from the shaking the vending machine is moved an inch forward and an inch to the left. That change would be detectable.
Everyone arguing against me is trying to focus the point that the event is such a short duration that it’s not detectable afterwards, and what I’ve been arguing the whole time and that people keep ignoring is that most of the time after an event happens that the environment around the event changes, and it’s detectable afterwards.
You either don’t know what binary search is or you completely missed the context of this conversation
You either don’t know what binary search is or you completely missed the context of this conversation
I’m a computer programmer. I know exactly what a binary search is. I’ve written binary searches before.
The search is to get you to the point where you can watch the video to see the crime happening, in hopes of indentifying the perpretrator.
Then you missed the point of this conversation
Then you missed the point of this conversation
You’re being intellectually dishonest, in an attempt to kill the message.
This is what was said in the origional OP pic…
You don’t watch the whole thing, he said. You use a binary search. You fast forward to halfway, see if the bike is there and, if it is, zoom to three quarters of the way through. But if it wasn’t there at the halfway mark, you rewind to a quarter of the way though. Its very quick. In fact, he had pointed out, if the CCTV footage stretched back to the dawn of humanity it would probably have taken an hour to find the moment of theft.
Binary search only works on sorted data, i.e. you know which side of the mid point is pointing towards the incident. If the incident leaves no trail, you can’t know whether you can discard the left side or the right side, making it a complicated linear search at that moment.
If the incident leaves no trail, you can’t know whether you can discard the left side or the right side
There’s a moment where the bike is there, then another when its not. The whole video, either way, will either from the beginning up to the point of theft have the bike there, or NOT have the bike there from the point of theft to the end of the video. The marker is the removal of the bike from the video lens.
But the comment you replied to wasn’t talking about bike thefts specifically, it was talking about unspecified situations that don’t leave traces. You responded to someone saying that binary search doesn’t work in situations that don’t leave cues not by arguing against the premise (e.g. “but no such event exists, everything leaves cues”), but by telling them that you simply have to look for the cues from the hypothetical event that didn’t leave any.
but by telling them that you simply have to look for the cues from the hypothetical event that didn’t leave any.
And my point is that the DID leave a clue that a binary search would pick up on, the disappearance of the bike.
That doesn’t apply to the comment you replied to.
Yes, it does…
But you will see the event happen though.
Not with a binary search.
Yes you will.
If the event lasts only a moment and leaves no visual cue (e.g. an assault).
How?
Yes.
I’m just a random guy stumbling across this thread hours after the fact. I want to say that after reading many of these comments. I feel like I’m starting to get a handle on what your position is. You aren’t wrong, but you are communicating your idea horribly.
Your position seems to be “Thankfully, many crimes do leave behind lasting visual cues, so you can still do a binary search for those situations if you are clever about what to look for.”
What you’ve actually been communicating is that “If there really was no lasting visual cue, then just find a lasting visual cue anyway, then do a binary search on that and it’ll work!” - It’s all about how you choose to present, order, and emphasize your comments. Your message is more than just the words you type. I hope this message helps clarify the debate and confusion for you and anyone else who stumbles upon this long chain.I appreciate you responding kindly, and your thoughts, thank you.
What you’ve actually been communicating is that “If there really was no lasting visual cue, then just find a lasting visual cue anyway, then do a binary search on that and it’ll work!
What I’ve been attempting to communicate, and I think have been expressing that, is that “no lasting visual cue” is not right (most of the time), its incorrect, and that there’s (almost) always a visual cue, and that you can do the binary search because there is. Not maybe, but there is, lasting visual cues (most of the time).
I disagreed with the point being asserted by the comment I initially replied to. I think people are getting hung up on my very initial comment, where I implied instead of being explicive, thinking my assumption was a well known one, just based on how I see the world operate (humans are messy). But how those replied to me seem that its not well known (or just not realized).
In hindsight, I should be more explicive, but that’s a horrible way to have to communicate, like if I have to pass every comment through a lawyer before posting it. You’d think people instead of instantly attacking would just have a conversation about try to understand my assumption. That didn’t come up until WAY later in the conversation tree, and only by a single person. There was way too many comments just attacking me with every hypothetical possiblity just to try and prove me wrong, and that, was wrong of them to do. Its not conversational, its bad group think.
Your message is more than just the words you type.
I was just telling my wife that the other day, its how you say that matters as much as what you say. I’m actually a well spoken person (on a good day at least). I’m honestly going to blame some of the confusion not on me, but on others with their hypotheticals, and confluencing how you scan a video, with how you search for sections of a video to scan, as adding to the confusion.
I hope this message helps clarify the debate and confusion for you and anyone else who stumbles upon this long chain.
Well, I think (saying this in 3rd person) what null was trying to do (gatekeeping censorship by telling others to not read my comments and calling me a troll) is really, really wrong. and bad for Lemmy, and I would have liked to have seen more people call him out on it, but instead he was rewarded with up votes. I truly don’t believe I deserved that, or that ANYBODY deserves that, and that his comment should be moderated.
And only because you mentioned it, I don’t feel confused, I feel anger. Anger over how I’ve been treated. It was just supposed to be a friendly conversation, expressing a counterpoint, and people responded by doing things they would not do in public to another’s face.
Yeah, pigs don’t like to be corrected. Or made to look like they don’t know what they’re doing.
And they absolutely hate ever doing anything about bicycle theft in particular.
I reported my bike stolen in college and I got a call the next day that they had found it parked in front of a nearby church.
It was stolen on a Sunday. I guess someone didn’t want to be late to service.
Probably added the theft to the sins they were confessing that day as well.
What you’re entering the third act of your love story and you have to get to the church in time to break up the wedding and declare your love, what’s a little bike theft? The universe will take care of it.
I have heard that very often. I wonder if bikes are harder to track down than other property for some reason.
smaller, therefore easier to hide. Not registered with a central authority like, for example, cars.
There’s plenty of cases where they don’t look for cars either.
Or the cops themselves just straight up steal the car themselves.
My wife’s car was ordered to be towed by, according to the impound lot, the police.
Neat thing was that there was no ticket with the car, no police station within 3 miles had a record of a ticket for her or the car, and the area she had parked had no signs that suggested it was illegal to park where she did, nor does the city have any ordinance about overnight parking.
Best we can figure, is a cop or the tow company that works with the city, just decided to tow a car for funsies and the 500 bucks it took to get it out of impound.
The police and every organization associated with them are corrupt to the core.
They only care about property loss when it involves rich people.
Which proves that cops really DO actually do their jobs.
Because protecting the property of the rich is the exact core purpose of policing.
Technically it’s maintaining social order. So get back to work menials or be reported to the Enforcers for organized discontent.
Maintaining social order, especially in the form of violent repression against demonstrations, indirectly protects the rich’s properties, so all in a day’s work.
Given the number of times I’ve seen cops on police forums and r/protectandserve use terms like “bikefags”, I think it’s just the typical cop disgust of anything they perceive to be weak or effeminate.
Yeah, I don’t get that. Bicycling requires strength and endurance. It exposes you to the elements. Why is sitting in a cushy car something some people think as being more macho? Is it that you’re in control of a heavier and more powerful machine?
Bicycling requires strength and endurance.
So does cleaning a house, but that’s “women’s work”.
Is it that you’re in control of a heavier and more powerful machine?
That’s it. You didn’t get it at first because made the mistake of associating manliness with things like patience, strength, hard work, endurance both of toil and hardship; all things that do make up ideals of manliness to normal people. But you need to approach it from the perspective of a wastrel, a weak, foolish, and lazy person who demands the respect and deference of being manly without putting in the hard work—something he has avoided all his life. He might praise hard work in abstract, but he has no discipline for it and doesn’t respect those who actually do it, he just considers them beneath him. To such a person, the defining aspect of manliness and machismo is mastery, mastery over others and their wills, and since mastery through work is a waste of time to him, he turns to shortcuts.
From there, it’s not hard to see where the thought process goes. Since strength is to him based on control and mastery, he picks something that gives him more command over the road in a direct and in-your-face way. The man who drives a lifted Ram 2500 can confront you by running you the fuck over. By contrast, in his opinion, cyclists are entitled jackasses in miniscule booty shorts who can only confront you on the road by screaming “CRITICAL MASS! FUCKING CAGER!” and throwing sparkplugs at your windows. The difference in power dynamic is proof enough to our friend of who the “real man” is.
To take the mentality to its conclusion, the easiest way to gain mastery in general is through authority, and the easiest way to get that, even easier than joining a gang, is by becoming a cop.
As a gay cyclist I know I’m doing something right by pissing off cops without doing anything wrong
Thank you for you service o7
Fun fact. Cops on average have lower IQ and often fail literacy tests. Furthermore it appears that critical thinking is discouraged in the job, with candidates being selected who lack critical thinking abilities over those that have them.
We need to have a chat about your definition of “fun”.
Certain departments specifically have IQ tests, in order to ensure you aren’t smart enough to easily get a better job elsewhere.
This internet myth has got to die. ONE case in ONE department, a quarter century ago, does not mean it’s a practice.
I think it’s more nefarious than that. Many departments want a good 'ol boys club where they’re the ultimate authority and they want their officers to fall in line rather than question department actions.
I’m sure it didn’t go well. If it was somehow framed in a sycophantic way where the police were led to believe it was their idea, I’m sure it would have gone better. Wait that might not be too difficult to do.
You just have to say there was a weird technique the Nazi’s liked to use.
They probably already know all Nazi techniques.
just tell them there is a black man at the moment of theft, they will get on it lickety split!
- Binary search: O(log(n))
- Sequential search: O(n)
- Linear search: O(n)
- Police ethnicity database search: O(0)
God damn, whoever came up with that is clever. I would have never come up with that on my own.
What if you had to guess a number between 0 and 100 and the other person (or an application) only told you if the number is bigger or smaller? That’s the form that’s usually presented to CS students and most people end up figuring it out on their own. Then the trick is knowing how to generalize it.
Without binary search, we would not have search engines today
Source article for the curious, and an unpaywalled copy on archive.is
I thought this had to be hyperbole, so I did the math myself. I’m assuming human history is 200,000 years as google says, and we want to narrow this down to the second the bike disappeared. also that the bike instantly vanished so there’s no partially existing bike.
each operation divides the time left in half, so to get from 200k years (6.311×10^12 seconds) to 1 would take ~42.58 divisions, call it 43. even if we take a minute on average to seek and decide whether the bike is there or not it would still be less than an hour of manual sorting
hell, at 60fps it would only take another 6 divisions to narrow it down to a single frame, still under an hour
edit: to use the entire hour we’d need a couple more universes worth of video time to sort through, 36.5 billion years worth to be exact. or a measly 609 million years if we need to find that single frame at 60fps
History is about 10k years, the 200k years is mostly pre-history. People didn’t write stuff down until they invented agriculture and needed to track trade between owners, workers, etc
True and interesting to note. OOP says ‘dawn of humanity’ though, not recorded history, so taking 200k as ‘human history’ is also valid.
Yeah, I’m used to the narrower meaning of “history”, meaning recorded. I like that definition as it lets you differentiate between it and prehistory.
Definitely a useful distinction.
A minute to decide if there is a bike in the picture really ?
As a robot, finding bikes in pictures is really hard, okay
Just watch at 3X!
Lemmy learns exponential math.
Mostly joking, thanks for doing the math.
I regularly bisect commits in the range of 200k (on the low end) for finding causes of bugs. It takes me minutes. Pretty crazy
Combine AI image/visual-pattern recognition and quantum computing, and this search could be completed before it was even started.
We can go deeper!
Ever heard of a logarithm? If you haven’t, you just reinvented it.
Also, your math is wrong: log base 2 of 200,000 is ~18
You did 200k years. You need to do 200k years as seconds (the 6.311e12 they mentioned). Their math is right.
Not sure why you’re acting like they claimed to invent the logarithm, either…
Police try to understand anything challenge (100% impossible) (gone sexual) (gone violent)
I once had a friend who was robbed of all kinds of stuff including a PS3, and that the guy was signed into his Netflix changing account profiles the very same day. I told him he can just get a tracking number by calling Playstation and that the active police officer can use it to track them. Thing is, the officer ghosted him for like 8 months despite having everything they needed to immediately find the exact location of the perpetrator actively using the stolen property.
This method will take forever to find the exact moment, said Officer Zeno.
This post just shows that the police rarely if ever review any video as this method would’ve been learned as a result of repeatedly reviewing video.
This is how I look for the best bits in porn
It’s got huge amounts of applicability in many lifestyles and situations that most people never realize until the moment arrives. I once played a fun game that had you guess a number between 1 and 1 Billion with them telling you higher or lower to earn your freedom. Takes a couple of minutes at most.
Your first guess should always be 500,000.
500,000,000*
Fast forward half way and see if the woman is still there?
I fast forward half way and pray she still isn’t slobbering on some knob at that point and they’ve gotten down to businesses already.
The final project in my instrumentation class was to tune a PID controller for a hot/cold mixing valve. I (CS/ENG) was paired up with an engineering student and a lot of it was throwing parameters in, seeing if weird shit happened, and then turning down or up based on the result. I had a programming final and something else I was supposed to be studying for, so I just started doing a binary search with the knobs. We got the thing tuned relatively fast and my partner acted like I was a wizard.
How do you do a binary search for an open-end scale (are PID params open-end?) and three knobs at the same time when they interdepend in their influence? I need to know since i have a PID tuning on my personal projects plate
It’s been ages, but we’d done rough calculations for the three controls so we roughly knew what we needed. Our teacher was big on manually tuning instead of just using formulas since he thought just running numbers “lacked artfulness.”
So we grabbed a point and started searching around manually. I think we were just tuning the derivative portion at that point, trying to get a fast response without the system without it going chaotic and noisy.
I’m realizing now that this would have been super useful when I worked in Loss Prevention way back when. Wish I had known…
Even without algorithm knowledge it should be fairly obvious that you can just fast forward several minutes and check if the item has gone missing.
Not the most efficient solution, but beats watching the entire tape in real time.
I’m a little surprised the police didn’t already know about that method. Seems like they’d encounter enough CCTV footage that’d it’d be standard training.
I once again overestimate the training levels of the police.
They probably do know. They just aren’t meant for protecting your personal property
It would have taken 5 minutes at most
My Graphics card/ssd wouldn’t be able to handle the skipping of such big files
