geometry – Given distance between cars, how to calculate the relative position and identify if the car is on my left or right?

I am doing decentralized control of vehicles. Assume I am a car with $2$ sensors, sensor $A$ in front of me and sensor $B$ behind. Using this sensors I can measure the distance from me to other vehicles $C,D$ and $E$. Apart from that I don’t have any other information and I cannot communicate with other cars.


  1. Calculate the distance between the other cars and their relative position.
  2. To figure out if the other cars are behind or in front of me.
  3. To figure out if the other cars are on my left or right.

Given length of $AC$, I know that finding relative position of car $C$ is a right triangle problem. $AC$ is hypotenuse, I need to find this right triangles legs. All possible right triangles lie in circle with diameter $AC$. However, without defining axis, it is not clear which tringle to choose. So using only sensor $A$ we cannot find the relative position.

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Now we draw another circle with diameter $BC$. And now the two circles will intersect at $J$ and that intersection is a point we need to calculate the relative position. Moreover, the intersection of these circles lie on the extension of line $AB$. This is very good, we can use line $AB$ as $y$ axis. Then to find a relative position of car $C$ we need to solve two equations with two unknowns:


where we assume $AB$ is known in priori.

We can do this for all cars on our right, i.e., $C$ and $D$. We know their relative position and using this information, we can even calculate the distance between them. However, we need to be careful, we need to know if they are in front of us or behind to be able to calculate the distance between them. But that can be checked comparing $AC$ vs $BC$. Since $AC<BC$, we know that car $B$ is on front, and since $AD>BD$, car $D$ is behind. Now we have achieved objectives $1$ and $2$.

However, I have a problem with a left side. I can calculate the car’s $E$ relative position, but I don’t know if it is on my right or left. So I cannot calculate distance $CE$ or $DE$ correctly, there is always two possible answers. Axis $y$ is well defined, comparing the distance from $A$ and $B$ to other cars, we can know if the other car is in $+y$ or $-y$ side. Axis $x$ is not well defined, from distance information we are not able to identify if the car is on our right or left. Is there any smart way to achieve the last objective without adding any additional sensors?

automobiles – Which countries don’t have a strong “car culture” (noisy cars & bikes)?

I currently live in Wales. Like most of the UK, it has a very high rate of people driving extremely loud cars and motorbikes, at all times of the day. Like a lot of people, the noise annoys me, but the police do nothing.
It’s like this in many other countries, i.e. Germany.

So my question is, which countries don’t have a high incidence / culture of people driving loud cars, whilst also being relatively well populated? (whilst Greenland would probably not have this, it’s also not a very practical country to live in). Thanks.

machine learning – What computational complexity classification does autonomous/self-driving cars belong to?

Self-driving car technology continues to attract popular attention and interest in today’s media, but how would a computer scientist explain the theoretical nature of the problem? For example, we are told that Sudoku and Go are examples of NP-completeness and PSPACE-completeness, and a range of practical progress has been made in dealing with these two categories. So similarly with autonomous vehicles, I think laypeople people (like myself) intuitively accept that learning to drive properly is a “problem”, but then, what is the underlying problem that such machine learning algorithms are trying to tackle?

I did some Googling around and found different articles and papers alluding to some parts or formal abstractions of the driving problem and/or maybe robotics being PSPACE-complete. So is that the answer basically? Or is it that the question is too vague to be answerable? Or even that there hasn’t been a clear understanding yet, because the area is fairly new? I’m just really curious, but didn’t find anything explaining this at a high level. But when I took CS in college, the professors would emphasize to programmers that understanding the nature of the problem can be very important, e.g. understanding if your specific problem is in P or is NP-complete, and so forth.

What to do when “no cars available” in Uber

This happens when no cars are available for your location at that given moment. If you can wait an hour or two for a taxi, I would suggest checking every 15 minutes and seeing if there’s any vehicle nearby. However, I would suggest you to take a regular cab straight away if there are no vehicles available.

If you are a tourist and you don’t know how popular uber might be in that area, going for a regular cab would be the best way to get around. Many cities have their own versions of uber (Colombo has Pickme) as well, so get some local knowledge as well.

I could not find any third party application that does this either, which is no surprise as there is very little practical value of such an app, unless uber was the only taxi service in the milky way.

lore – Are there streets where cars can drive in the Ork/Seattle Underground?

In areas controlled by prominent factions/gangs/law enforcement, absolutely.

The underground is described as containing a significant population of orks, trolls, and others in various conditions which aren’t just tents in storm drains but also contains bases, armouries, tourist traps, malls, law enforcement offices, workspaces, workshops, corporate outlets and decent living accommodations (stretching to the even sybaritic).

This is a city of 200,000 people.

Now what you’re thinking of – ‘small cramped tunnels’ – is a description of the seattle underground in the 1900s – it’s 2083, omae. There’s three main ‘levels’ of the underground, the dwarf controlled tourist trap (still got lots and lots of orks and trolls) which has KE and corporate presence, medic contracts, all the normal hustle and bustle of life. It’s an absolute shoe-in that this has some areas where you can drive in, using car lifts to get to and from the surface (probably at a significant fee), as well as public transportation.

The Skraacha-controlled areas, which are generally described as more run down but still not like Redmond level bad, and which are usually ‘lower’ will likely have some areas that have public transportation or drivable roads and other places with narrower confines or throughways blocked by rubble/trash.

Then there’s the uncontrolled areas which are very unlikely to be drivable, which are abandoned areas taken over by ghouls, spirits, cultists, you name it they’ve got it.

Remember, the key thing about the underground is that it’s Big. Orks and other people have been digging and building down there for decades and decades, with all the singleminded focus of people with nowhere else to go.

However – you’ll find official sources that contradict what I just told you. Thanks to catalyst’s practice of hiring random freelancers and not doing any editing, SR5 (and 4, and 6) suffer from lore fragmentation – you’ll find contradictions, sometimes wild ones, scattered through the various splatbooks and ‘canon novels’. So in the end if you want the ork underground to be a warren of tiny, trash-filled tunnels that’s really up to you as a GM – as long as you’re consistent with your seattle, that’s basically the best you’re going to get out of current canon, which is generally very vague at the best of times and disagrees with itself on top of being frankly unbelievable at the worst.

racing – How can one achieve the mechanic of hitting cars or bumping into them like in Burnout games’ takedown modes?

I’m working on a racing game and I would like to work on a similar feature. The closest I’ve come to achieving that is by adding a bouncy material to my cars colliders.

I don’t have that much experience in making games so I’d appreciate any help I could get about the subject.