[HN Gopher] Art of Roads in Games
___________________________________________________________________
Art of Roads in Games
Author : linolevan
Score : 570 points
Date : 2026-02-08 21:05 UTC (1 days ago)
(HTM) web link (sandboxspirit.com)
(TXT) w3m dump (sandboxspirit.com)
| zabzonk wrote:
| Be like the Romans - make them all straight lines :-)
|
| Of course the Romans didn't give a shit who's property rights
| they might be violating. I live in Lincolnshire UK, where Roman
| roads are still used. The last one that got changed was years ago
| when they had to put a kink in Ermine Street (now the A15) at RAF
| Scampton when they extended the runway to accommodate Vulcan
| bombers.
| oaiey wrote:
| In my area, streets are often church tower to church tower.
| From the middle ages. You can nowadays drive these streets and
| the middle line indicators align perfectly with the church
| tower showing up. I think the church /church based government
| share that property right understanding of the Romans :)
| plomme wrote:
| The romans did care about property lines! Romes' second
| aqueduct was held up when land owner Crassus refused to give up
| private land for its construction. Check out the article for a
| fascinating read: https://en.wikipedia.org/wiki/Roman_aqueduct
| closewith wrote:
| What an ugly attitude for the landowner to have held. There
| should be a word for that.
| serious_angel wrote:
| Thank you very much... Ineffably magnificent, as always...
|
| Related: https://www.pushing-pixels.org/2014/04/04/the-craft-of-
| scree... (The craft of screen graphics and movie user interfaces
| - interview with Jorge Almeida...)
| heliumtera wrote:
| The tech seems really cool, but the road showed in the examples
| is not any less insane, like, why?
| hresvelgr wrote:
| That's the point? Even though they are complex, the improved
| roads all use circular arcs which guarantee a baseline of good
| drivability.
| aerio wrote:
| Their animated gif at the very end of their own tech seems very
| sane?
|
| I wish they'd actually shown more/talked about it though.
| Ef996 wrote:
| Will share more soon. I have some more recordings of it on x
| https://x.com/SandboxSpirit if you're interested.
| bombcar wrote:
| Another aspect of these games is the subtle scale issues that
| aren't readily apparent - even the newest biggest city simulators
| are fractions of the size of a real city.
|
| Road and rail curves are _massive_ and it's hard to understand
| just how big they are without having to actually walking them.
| prawn wrote:
| I regularly drive what I thought of as a quite winding road.
| Visitors drive it cautiously. It was funny one time looking at
| the satellite view and thinking "Wait, where is the tight bendy
| section?" Everything looked like very gentle curves; probably
| closer to straight lines.
| hibikir wrote:
| You can find in developer notes for city sims that sometimes
| they've tried to keep sizes of roads and parking lots to scale,
| and then they realize it's all low density and uninteresting,
| kind of like real aerial photography of a typical US city.
|
| So the difference in scale between real life and the sims is
| 100% on purpose, as more realism makes the game worse. Just
| like they don't ask for a long permitting system for anything
| to get built, or demand a decade of discussion and probable
| lawsuits before you can move move a road, or rebuild an
| intersection.
| left-struck wrote:
| Having played many city building games though I've always
| desired more depth and realism. Like the more I play them the
| more I want out of them. I wish power lines were limited in
| capacity and had to be stepped up and down via transformers
| (Workers & Resources does this) I wish I could make decisions
| about every intersection and every lane (cities skyline mods
| allow this) etc. Anyway I think there's an audience for more
| realistic games in general, even if most people would find
| them less fun.
| oaiey wrote:
| At a certain point these simulators would be so intense
| that your joy for the game could be your joy for real
| employment in a city :)
|
| The statement reversed, you might loose your joy because
| working in the game is no longer fun.
|
| I get you but just want to say: careful what you wish for
| :)
| chongli wrote:
| I love SimCity 2000 and these roads look really cool but I'd
| really like to see a city-builder go in a different direction.
|
| One of the biggest problems with North American cities is their
| endless, car-centric suburban sprawl. SimCity games may be really
| fun to play but they seem to reinforce this problem and anyone
| who grows up playing them will not learn about alternatives for
| more livable cities.
|
| New Urbanism, traditional neighbourhood design, streetcar
| suburbs, one-way streets, bike paths, walking paths, mixed-zone
| walkable villages (light commercial with residential), smaller
| single-family houses and duplexes, triplexes, houses behind
| houses. Many of these are older and more traditional techniques
| to yield higher density neighbourhoods without building up to
| large apartment buildings.
|
| It would be really cool to see a game that focused more on
| creating these kinds of realistic and aspirational living spaces
| instead of the usual cookie-cutter suburbs linked up by huge
| roads and a large downtown core.
| mh2266 wrote:
| this is definitely doable in CS (+mods), search YouTube for
| "cities skylines European" or something like that.
|
| you need "plop the growables" and "move it" mods at minimum to
| nudge all the buildings close together.
| IMTDb wrote:
| There are plenty of "chill and peaceful" city and town builders
| that trade realism for prettier, more idealized places.
|
| In more simulation-focused games, cycling and walking paths are
| often available, and you can use them, but they come with many
| of the same constraints they face in the real world. In
| practice, that means they are usually not efficient as the
| primary way to move large numbers of people across a large
| city.
|
| Reading your comment, it sounds like you want a game that is
| realistic in most respects, but treats transportation
| differently, in a way that makes your preferred options the
| optimal strategy. That is going to be hard to find, since
| transportation is a core part of city-building sims, and
| developers tend to pick either realism or a more
| utopian/fantasy model rather than mixing both in a single game.
| Tarrosion wrote:
| [citation needed] that some combination of "New Urbanism,
| traditional neighbourhood design, streetcar suburbs, one-way
| streets, bike paths, walking paths, mixed-zone walkable
| villages (light commercial with residential), smaller single-
| family houses and duplexes, triplexes, houses behind houses."
| is not in fact optimal! (For certain objective functions)
| chongli wrote:
| That's not what I want at all. I want a more realistic sim
| that deals with issues such as sprawl, food deserts,
| transportation elasticity of demand, mental health issues
| (and their impact on crime and productivity), and a network-
| flow theoretical model of transportation and commuting
| contributes to all this. Building a bunch of sprawling
| suburbs that feed into a dense downtown core should make your
| citizens' commute times shoot way up and lead to misery.
|
| A well-built large city isn't just going to be 100% biking
| and walking paths, it's going to have streetcars, light rail
| transit, subways, and buses as well as roads with cars. The
| difference is that people shouldn't be forced to commute
| across the entire city to get to work because you decided to
| cram all of the commercial zoning into one downtown core.
| jmye wrote:
| > The difference is that people shouldn't be forced to
| commute across the entire city to get to work because you
| decided to cram all of the commercial zoning into one
| downtown core.
|
| Isn't the point that they _should_ be, if that 's how I
| choose to build a city, and they don't _have_ to be, if you
| choose to build it otherwise? The entire point of a sandbox
| city-builder is, I assume, that it 's a sandbox, and not a
| dogmatic interpretation of a childish Reddit meme.
| chongli wrote:
| It was pointed out elsewhere in this thread that SimCity
| already distorts reality in an ideological way: it lets
| you have tons of traffic without worrying about parking.
| It just gives you magical free underground parking
| everywhere that you never have to think about, in order
| to avoid the usual suburban parking sprawl hellscape.
| bombcar wrote:
| The original SimCity was perfection - you could build no
| roads and nothing but rail! ;)
|
| Cities Skylines with all the DLC _and_ the right
| transportation mods gets pretty "realistic" in that you can
| build a transit paradise but the car still exists.
| Qwertious wrote:
| Car-centric transportation is not efficient. Not remotely.
| They have absolutely terrible bandwidth, and they balloon the
| size of cities apart the more you try to increase the speed
| to bring them closer together.
|
| If you think Simcity and Cities: Skylines are realistic
| depictions, then ask yourself why Simcity famously has _no
| visible parking whatsoever_ (or don 't: the devs are on
| record saying they excluded it because it made the cities
| look terrible, there's no need to speculate here), or ask
| yourself why Cities: Skyline added _car pokeballs_ (where
| drivers get out of the car and _put the car in their pocket_
| ) or straight-up delete cars when traffic gets too heavy.
| matsemann wrote:
| > Reading your comment, it sounds like you want a game that
| is realistic in most respects, but treats transportation
| differently,
|
| It's the opposite, no? Most city builders cheat to be able to
| be fun. Like, with the amount of roads one build in Sim City,
| half the map would have had to been parking lots to account
| for that amount of traffic. But that's boring gameplay, so
| they remove that constraint to make a fun game. Aka you never
| have to deal with the consequences of making your city car
| dependent.
|
| Edit: See another comment from CalRobert about exactly this.
| prmoustache wrote:
| You have a weird definition of "realism".
| GaryBluto wrote:
| > SimCity games may be really fun to play but they seem to
| reinforce this problem and anyone who grows up playing them
| will not learn about alternatives for more livable cities.
|
| That's because SimCity is not a tool for preaching your
| personal opinions of what makes "more livable cities" to people
| who more often than not want to design semi-realistic, typical
| cities in an entertaining strategy game.
|
| If you want to make your perfect city builder, go ahead, it's
| easier than ever now for somebody to create a game. Just don't
| expect everybody else to share your view of "aspirational",
| more so if you actively punish traditional city structures.
| jak6jak wrote:
| OP must of hit a nerve here but In games like city skylines a
| big difficulty of large cities built in the game is handling
| car traffic. A lot of which is solved by public transport,
| walking paths and other "apirational" city structures that
| are hard to realize in real life. I've watched alot of fun
| videos on youTube of a certain youtuber apply these
| techniques to other people's saves to great success. It's
| honestly a fun challenge to solve.
| prmoustache wrote:
| > to people who more often than not want to design semi-
| realistic, typical cities in an entertaining strategy
| game.[...] more so if you actively punish traditional city
| structures.
|
| What you call "typical" and "traditional" is not in any way
| universal.
|
| Or you haven't travelled a lot.
| stronglikedan wrote:
| > One of the biggest problems with North American cities is
| their endless, car-centric suburban sprawl.
|
| Most people consider that a benefit. It's just as livable as
| anywhere else. Just different.
| vineyardmike wrote:
| > It's just as livable as anywhere else
|
| People are totally entitled to like what they like, and
| that's OK. Everyone has something that works for them, and
| this world has a great variety of options available but the
| "car-centric suburban sprawl" is linked to various negative
| mental and physical health consequences. Negative health
| consequences, IMO, isn't "just as livable".
|
| As a simple example, when people walk more during commuting
| instead of drive, they tend to be healthier. There are other
| more nuance (but studied) impacts, such as increased car
| accidents, mental impacts from increased isolation, etc. In
| America, there is even a correlation between how car-centric
| a community is and how often individuals are willing to seek
| out healthcare (even when accounting for access and
| affordability).
| account42 wrote:
| Yeah it's strange how some people think that squeezing people
| like sardines without any space for personal gardens is
| supposed to be a good thing. Density in European cities is
| mostly a historical artifact and something objectively
| chosen.
| matsemann wrote:
| Huh, wonder what takes up all the space that could've been
| parks and gardens (hint: it's made of asphalt)
| prmoustache wrote:
| If you like living and spending all your day in your car yes.
| jmye wrote:
| I don't spend anything close to "all my day" in a car - I'm
| not sure what the absolutely over-the-top and completely-
| detached-from-reality, snide hyperbole adds, here.
| prmoustache wrote:
| Well that is certainly how it feels when I am in a city
| in north america.
|
| A small errand that takes me 5 to 10min in my hometown
| takes me 45min to 2h in suburbialand. Worse, mutualizing
| errands do not even reduce the overhead of a single trip
| because infrastructure is usually made in such a car
| centric way that it makes it super inconvenient if not
| downright dangerous to walk from one huge parking lot to
| another one a couple of blocks away so you are kind of
| pushed to move your car, sometimes navigate a stupidly
| long loop to simply turn around and go on the other side
| of a stroad.
|
| By the end of the day you realize you have barely done
| anything.
|
| Funnily it makes it worse for both drivers and non
| drivers.
|
| At home I usually opt to not take the car, not because it
| would be slow but because in many cases it is silly. It
| would be too short for the engine to even warmup and I
| would not have the chance to enjoy some time outside
| and/or exercise at the same time.
|
| I totally see the impact spending so much time in the car
| and traffic has on my in law family's stress level and
| they do complain a lot about it while being seemingly
| unable to envision a better way of living and push for it
| at political level. It is also super bad on the security
| side of things because they often opt to take/make calls
| while driving for it to not make it time totally lost and
| aren't just as focused as they should be on the road.
| MindSpunk wrote:
| Do we really need to jump onto a tangent about evil cars and
| evil car infrastructure on a post about b-splines and curve
| sections?
|
| Everything in the article applies equally to trains and rails.
|
| We get enough complaining about evil car-centric city designs
| on the posts directly about cars thanks.
| dcsommer wrote:
| I think GP is simply identifying a potential popular niche
| that could be satisfied in a future city builder game, which
| seems quite on topic.
| throwerxyz wrote:
| Those areas aren't better to live in. They're just older parts
| of older towns so they don't have much wiggle room. The wiggle
| room was amazing for the more modern countries, except now we
| wiggle in a different direction too. An equal middle can be
| seen in Asian cities in Korea and China. They mix high density
| with high quality of life and little self sacrificing.
|
| Neither US or Europe do living areas well due to their
| historical constraints.
| CalRobert wrote:
| It's subjective but many of us strongly disagree.
|
| And, of course, the fact that the areas you say "aren't
| better to live in" also tend to be extremely expensive
| doesn't make a lot of sense.
| account42 wrote:
| Except for gates communities, living cost is mostly a
| function of closeness to high paying jobs.
| CalRobert wrote:
| I don't think that counters what I wrote? One of the
| benefits of higher density is having more high paying
| jobs nearby.
| CalRobert wrote:
| The creators SimCity itself were aware of the problems you
| mention. Ever notice how there's no parking lots?
|
| https://humantransit.org/2013/05/how-sim-city-greenwashes-pa...
| chongli wrote:
| They were aware of the problem and they covered it up, rather
| than try to show better ways of living. It's unintentional
| propaganda for the crappy ways we build our cities. It's
| worse than if they'd just show things how they really are.
| nine_k wrote:
| When I played Sim City, I gladly built super-dense
| neighborhoods with high-rises facing parks, and mass transit,
| Le Corbusier style. One reason was that they brought in
| enormous income, another, that they looked cool.
| muzani wrote:
| I was fascinated by them since reading a guide for Cities:
| Skylines that said that roads were like trees. There's a trunk
| that moves large amounts of nutrients and little branches that
| distribute the nutrients to the leaves. Such simple rules, but
| such complex and deterministic results.
| genpfault wrote:
| https://www.redblobgames.com/articles/curved-paths/
| Ef996 wrote:
| Yes, I don't even know how I didn't know about this at the time
| of wiring the article. But a must read for sure!
| antif wrote:
| One game that had a different perspective (first person mmo), but
| a fun network of road building in a simulated wilderness .. Wurm
| Online
| raincole wrote:
| Cool shit!
|
| > Do 99% of city-builder players care what shape the corner
| radius of the intersection has? Most likely, no.
|
| Maybe not... but out of all the players who care corner radius of
| roads in games, 99% of them probably are into city-builder!
| hobofan wrote:
| The corner radius discussed in the article is utopian and also
| only works in street layouts that prioritize car driveability
| over everything else.
|
| A "properly rounded corner" at an intersection as alluded in
| the article is one that's great for cars (as they don't have to
| slow down much or have a tight turn. However, they are awful as
| pedestrian crossings if you want to do a double crossing, as
| you have to traverse additional distance. They are also much
| more space-inefficient, which isn't viable in a densely built
| urban environment.
| inflam52 wrote:
| Timely article for me! I just went through this in my little
| SimCity remake for MicroPython:
|
| https://github.com/chrisdiana/TinyCity/blob/6c3a7337788655b5...
| hirako2000 wrote:
| Articles like these are the reason I continue to check
| hackernews.
|
| Author please keep writing.
| Ef996 wrote:
| For sure I will. Thanks a lot for your interest. To anybody's
| disappointment, I didn't even know Hacker News was a thing
| until I saw a ton of traffic coming from it. But I guess I'll
| be more active here since there are a lot of like-minded
| people.
| hirako2000 wrote:
| Hackernews is notorious for causing outages when a link to a
| self hosted site trends.
|
| Beware if you post article's in there.
|
| I also do graphic processing and now with ML, contact me if
| you ever want to share though, contact via my profile
| technothrasher wrote:
| > Hackernews is notorious for causing outages when a link
| to a self hosted site trends.
|
| This made me briefly nostalgic for the old glory days of
| Slashdot, which is the first place I recall that would
| cause the "hug of death".
| mlrtime wrote:
| /. affect was a real thing for sure. I'm not sure it
| happens much on HN.
|
| My guess is a combination of tech being better and HN
| having lower volume vs peak /. (before digg&reddit).
| ChoGGi wrote:
| I believe the hug of death is Reddit, Slashdot was
| slashdotted.
| stravant wrote:
| People who made tools that generate roads using circular arc
| spines unite: https://devforum.roblox.com/t/new-geomtools-
| plugin-quickroad...
| abcde666777 wrote:
| There's so many things in games that are taken for granted at
| play time but which actually take a lot of thinking and work to
| get right. Roads for instance aren't something which your typical
| player will look too closely at... but they will notice if they
| look or behave in a way that seems wrong.
|
| I've been playing Kingdom Come 2 of late, and I find it's natural
| to just kind of take the world they've created for granted - just
| like we do the real world. But when you actually stop and look
| you have to consider that every one of the finely crafted details
| was built by someone's sweat and tears, be it artists,
| programmers, or designers at edit time.
|
| No wonder it's an industry of crunch, the work involved can be
| uniquely daunting.
| shalmanese wrote:
| Another area of hidden complexity is doors in video games.
| Almost no game has life sized doors because they introduce
| gameplay issues, almost all doors in video games are at least
| 30% bigger than in real life and you see an overabundance of
| sliding doors vs swinging doors because of the complexity
| swinging doors bring to video game physics.
|
| https://lizengland.com/blog/the-door-problem/
|
| https://www.ign.com/articles/putting-doors-in-video-games-is...
| bestham wrote:
| This was also confirmed by a Valve developer recently about a
| bug in HL2:
|
| https://mastodon.gamedev.place/@TomF/115589925206309168
| yoricm wrote:
| That's an impressive bug hunt. Same code, different
| behavior. I can't imagine how much time the guy spent on
| finding this one. And how much satisfaction once he finally
| nailed it.
| account42 wrote:
| Also in their VR titles Valve made all doors swing in both
| directions because that feels more natural to players when
| there is no haptic feedback from not being able to push
| open a door.
|
| The scale difference mentioned in gp isn't just doors
| though but any structure you can pass through. Many games
| houses with larger interiors than exteriors and video game
| ventilation ducts are comically large.
| BrtByte wrote:
| Yep, the most impressive work in games is the stuff players
| never consciously think about
| asimovDev wrote:
| I absolutely love how Skyrim's world is built. A lot of details
| that would fly past most players' attention are quite thought
| through. How roads connect, where do rivers intersect, where do
| lakes get their water from, in which direction do they flow
| etc.
| LanceH wrote:
| > There's so many things in games that are taken for granted at
| play time but which actually take a lot of thinking and work to
| get right.
|
| I have a small list of these things in game dev. Over the
| years, I found some games that were more playable (in my
| opinion) than I thought they deserved to be. Kind of like a
| well written book with a bad story.
|
| For me at least, the number one most important thing is how
| well the character -- person, car, spaceship, whatever --
| moves. Does it handle well, as expected. I'm at the point where
| I think this may be the single most important aspect of a game
| that finds itself in a competitive space.
|
| I think blizzard stands out for this with Overwatch and World
| of Warcraft. They avoid the jerky start and stops with their
| characters. Their characters feel both performant and natural
| at the same time, adhering to reality but breaking physics as
| necessary (air strafing for example).
|
| Building out roads correctly feels like an offshoot of this for
| games which include cars. A car should be able to navigate a
| turn without going through weird contortions as it hits pinch
| points, or unnatural wiggles when roads join.
| amatecha wrote:
| Ah yeah, this is actually part of why I never complete games..
| I spend so much time messing around looking at all the cool
| little details, exploring the environment and generally
| "experiencing the place" moreso that pursuing game mechanics or
| completing levels/quests/etc. ... some of my favorite games,
| I've played probably like 1/4 of lol
| heyitssim wrote:
| My version of OP's roads problem is blob autotiling - how tiles
| connect to their neighbors. 256 possible neighbor combinations
| reduce to 47 valid patterns once you realize corners only matter
| when both adjacent edges are present. You paint a semantic type
| like "wall", the system resolves the right tile from those 47
| patterns - but painting one tile cascades outward, neighbors re-
| resolve, which triggers their neighbors, and you're tracking
| stale state to keep it all consistent. Same underlying problem as
| road segments affecting connected intersections.
|
| I've been trying to make this as easy as possible for non
| technical people to draw terrain in craftmygame (the game engine
| I'm building) here's what the terrain painting looks like in the
| editor so far :
| https://youtu.be/bFrUYM2t3ZA?si=tw1LqBWR7Uyn08lR&t=37
| czheo wrote:
| I studied urban planning back in the university and one of the
| classes was road design. Though I forgot most, one part of the
| class was about how to design roads with curves that's safe for
| cars. This post just brought that memory back to me.
| smhinsey wrote:
| This is a really interesting approach but I'm curious to see how
| it translates to the actual mesh extrusion, or whatever 3d
| technique they adopt. It's relatively easy to do this in 2d, it's
| the 3d solution that accommodates terrain variation that
| introduces the real explosion of complexity
| acherion wrote:
| The author might get a kick out of an upcoming game called
| Junxions, which is a sandbox game to just do that... create road
| junctions.
|
| The subreddit is here: https://www.reddit.com/r/Junxions/
|
| Sure they teased that they've made their own solution, but I
| think Junxions should scratch the itch of most of us here
| interested in this kind of game.
| Ef996 wrote:
| Hello, I am the creator of this road system. The thing is that
| I myself don't even know what I want to do with it. lol. Maybe
| an asset or a game (a bit scared to jump in a full fledge game
| to be honest).
|
| I am a fun of Junxions my self which follow closely. But the
| approach in my system if very different. Junxions creator uses
| the same kind of node base/bezier shapes paradigm where
| intersections happen as node graphs and not automatically as
| collisions between road segments. It's hard to explain but I am
| planning to dive into more details on why those two approaches
| are different in my next blog deep dive.
| Lichtso wrote:
| > The thing is that I myself don't even know what I want to
| do with it.
|
| Embrace the next challenge: Instead of roads on parabolic
| (Euclidean) geometry, have roads on elliptic (non-Euclidean)
| geometry, like the surface of a sphere. Plus, on a sphere
| every line is already a circular arc anyway (no matter if
| straight or bent, the difference is just the center, radius
| and normals). Thus, this system of circular arc segments
| really lends itself to such a space.
|
| Little prince style micro planets with their own miniature
| infrastructure will always have a special place in my heart.
| Half a year ago I started with laying out the basics
| https://github.com/Lichtso/bevy_ellipsoid_billboard
| https://github.com/Lichtso/bevy_geodesic_grid but got
| distracted by fixing some engine bugs in Bevy along the way.
| That reminds me I have to update to the newest engine version
| ...
|
| anyway you can find some of the roads on spheres stuff here:
| https://github.com/Lichtso/bevy_geodesic_grid/blob/main/src/.
| .. it can not only generate the extrusion mesh but also
| calculate how the mesh overlaps with a geodesic grid of
| triangular tiles on the surface.
| Ef996 wrote:
| Thanks for references! I initially considered bevy for this
| but I was a bit scared it was not mature enough. How do you
| find it now?
| Lichtso wrote:
| Really depends: In some areas it is quite advanced
| (rendering) and in others it is lacking / underdeveloped
| (editors / tooling). But there is an incredible amount of
| progress and also churn in keeping up with that.
|
| https://thisweekinbevy.com/ https://bevy.org/news/
| murkt wrote:
| Sounds pretty fun! Do you have any screenshots to show?
| JamesTRexx wrote:
| Go full science fiction and enable vertical or even upside-
| down roads for a 3D experience. :-)
|
| Imagine an environment where ground/walls/ceilings always
| have gravity and one can build literal city mazes in
| horizontal and vertical directions. All that traffic going
| everywhere, oh my..
| BrtByte wrote:
| If someone just wants to zen out building perfect merges,
| Junxions looks great. If someone wants to fight Bezier math
| demons at 2am because offset curves keep exploding... this
| article probably hits closer to home
| jak6jak wrote:
| Everyone is raving about this article. It feels so much like a
| tease to me. Maybe I'm just impatient idk.
| empiko wrote:
| I'm with you. I hope that the other posts will also pop up
| here.
| Gare wrote:
| > And they are also... a math nightmare. Differential geometry.
| Integrals. Oh my... Which is probably why most games don't even
| dare.
|
| Wonder if cubic parabola (used by some railways, and visually
| near indistinguishable from clothoid) has easier maths.
| raphlinus wrote:
| I don't agree that the clothoid is a math nightmare. One of the
| central problems you have to solve for roads is the offset
| curve. And a clothoid is extremely unusual in that its offset
| curve has a clean analytic solution. This won't be the case for
| the cubic parabola (which is really just a special case of the
| cubic Bezier).
|
| Sure, you have to have some facility with math to use
| clothoids, but I think the only other curve that will actually
| be _simpler_ is circular arcs.
| Ef996 wrote:
| I mean they are not a math nightmare per se if you're
| comfortable with the theory. What I meant is that they become
| comparatively complex to integrate into a system like this.
| Think about arc length, compute intersections,
| reparametrization, etc., and with clothoids that usually
| means some complex numerical algorithms.
|
| Using circular arcs or even simple third-degree polynomials
| (like cubic parabolas) reduces many of those operations to
| trivial O(1) function calls, which makes them much cheaper to
| evaluate and manipulate procedurally, especially when you're
| computing it 60 times per frame
| masfuerte wrote:
| You might be familiar with these, but GP wrote a couple of
| excellent pieces on Euler spirals:
|
| https://raphlinus.github.io/curves/2021/02/19/parallel-
| curve...
|
| https://levien.com/phd/euler_hist.pdf
| Ef996 wrote:
| Glad you mentioned it. Cubic parabolas were actually used by
| eraly railway engineers as good approximations of clothoids
| back when numerically solving a true euler spiral was a
| daunting task.
|
| They are visually very close because their curvature
| increseases approximately linearly along the curve but not
| exactly. Mathematically speaking if you wirte the cubic
| parabola as something like y = kx^3, the second derivative
| (which give the curvature) grows linearly with x which makes it
| behave similary in gentle transitions.
|
| The problem is that the second derivative is not enough alone
| for having a true smooth curvature. The real curvature formula
| has in the denominator the first derivative as well (slope)
| making it not increase perfectly linearly along the curve.
| (denominator becomes larger and larger as x incrases)
|
| But yeah, cubic parabola is basaically a good enough
| approximation. Might be a good solution for a system like this.
| noduerme wrote:
| Ahhh.. this is a writer after my own heart. Absolutely brilliant
| write-up. I had the same obsession with roads, from SimCity
| onward; they're the circulatory system of any city, and never in
| the history of cities or the history of circulatory systems have
| the vessels been straight lines. The streets of a European or
| Asian village usually tell a story about how roads were built
| over the fastest footpath from the outskirts to the center, then
| over time amended to go around some buildings that were built in
| the way. Whereas roads in rural parts where I come from run in
| long straight lines and then suddenly swerve to get around a
| piece of land that a farmer wouldn't sell. But grids only exist
| in some parts of the few cities that were built mostly by
| colonial powers, or developed later with master planning. And
| even those grids usually split from their original orientation to
| becoming north-south at some point in in the city's development,
| leading to the interesting downtown triangle blocks of cities
| like Portland, San Francisco, Los Angeles, Seattle, New York.
| Other cities started to grid around their core footpath villages,
| like Madrid, Barcelona.
|
| The cities I find the most interesting (for roads) are the ones
| which kept gridding out in new directions to follow the course of
| a river. Cities like Buenos Aires, New Orleans, and Saigon, where
| the original paths followed curves around the river bends,
| resulting in multiple intersecting grids.
|
| The intersections and division boulevards between grids are, of
| course, the most beautiful and architecturally interesting parts
| of any city. They are where the blocks are strangely shaped and
| the buildings can't be rectangular, and usually where every inch
| of land is at a premium as well. It would be nice if a city-
| builder could simulate that aspect of urban growth: The shift
| from village center to grid, and old grid to new grid.
| Ef996 wrote:
| Very happy reading this because I was always thinking exactly
| the same about historical games. One of my turn offs for any
| historical city building is when they are grid based. I always
| found that to be highly unrealistic, but I yeah, was aware that
| it was just some unneeded complexity and just my nerdy
| nitpicks. The point you make would've actually been a strong
| argument in my article. Too bad I didn't have the inspiration
| to include it. The way historical cities developed in an
| ordered yet intricate way without any central planning (same as
| ant colonies) is actually very fascinating and I might write
| about this at some point.
| noduerme wrote:
| Regarding modern roadways and viaducts that pass around
| medieval city cores, it's fascinating how they can be seen
| and still not seen. I tried to do this in Cities Skylines II
| for awhile, building very narrow streets in "organic" city
| centers with low-to-mid density, and then transitioning to a
| new city grid around the old center. Finally, superimposing
| highways and tunnels without destroying the original
| historical core. There were some beautiful results, but the
| traffic jams were astounding, even with limits on the city
| center roads and highway exits. This is the way cities
| actually grew, so to me it's much more interesting to
| simulate than a "perfect" city built all at once. One thing
| that was fun in SimCity 3000 was that certain technologies
| didn't become available until you had a certain population. I
| would almost wish that a city-builder now would allow you to
| take that to the extreme: Spend 200 years with horse-drawn
| carts before you can pave a road, and _then_ figure out what
| to do with the mess. But more than anything: Oddly shaped
| buildings that fit into oddly shaped lots, which are not
| limited to hotdog stands.
| Ef996 wrote:
| Haha. I myself tried to play CS like that. Start with a
| historical core. The thing is the way the game is
| implemented buildings only have rectangular footprints
| while in reality buildings occupy the spaces more
| organically. I actually spent quite some time on google
| maps trying to see what pattern historical buildings
| followed to fill in spaces but couldn't get a definitive
| answer. I drafted it at some point in sketchup. Here is the
| result
|
| https://imgur.com/a/procedurally-generated-buildings-that-
| or...
| orbit7 wrote:
| Can relate the fascination with roads I use to like drawing them
| loads as a kid. I find Satisfactory the most satisfying for
| building transport systems (and building generally) your work
| incorporated into a mod for that would be really cool.
| Ef996 wrote:
| I am a huge fan of satisfactory as well (probably no surprise
| for anyone)
| pmontra wrote:
| The bit about the clothoid finally made me understand the odd
| shape of highway junctions. I always wondered why they want me to
| enter turns fast and then slow down progressively until the turn
| becomes a new straight. Unfortunately sometimes that straight is
| the highway, and they should give us plenty of space to build up
| speed and match the traffic inside the highway. Sometimes they
| do, sometimes they don't.
| brnt wrote:
| This is why I like Dutch road design, there's a legally
| required minimum (I think it's 200m, but 300m is more common)
| for onramps, and we are taught not to merge before you've
| reached the maximum speed on the road you're merging too, so
| that you cause minimal disturbance to the traffic currently
| there. (Think like a zipper.)
|
| I live near the border with Germany, and these guys are used to
| short ramps and so just merge well below the speed other
| traffic are going, expecting others to yield. (And many locals
| also drive like that unfortunately.) So uncivilized.
| Wistar wrote:
| [Adds "clothoid" to vocabulary]
| Arn_Thor wrote:
| "Do 99% of city-builder players care what shape the corner radius
| of the intersection has? Most likely, no."
|
| Finally, I am part of the 1%!
| BrtByte wrote:
| Once you do care, there's no going back
| rob74 wrote:
| > _I think roads lie at the heart of every city builder. It's the
| fabric on which cities are built._
|
| To paraphrase the article, this is what urban planners have
| nightmares about. _Roads_ (as in: things made for cars) aren 't
| the fabric of a city, _streets_ (as in: things made not only for
| cars, but also for pedestrians, cyclists, public transport etc.)
| are. See also: https://en.wikipedia.org/wiki/Stroad
| kqr wrote:
| I had never considered there is a difference between the two
| words, but Wikipedia backs it up:
|
| > The word _street_ is still sometimes used informally as a
| synonym for _road_ , but city residents and urban planners draw
| a significant modern distinction: a road's main function is
| _transportation_ , while streets facilitate _public
| interaction_.
|
| Even with this clarification, though, I think you unfairly
| characterise the quote from the article. Modern society has an
| insane demand for transportation. Roads - the medium on which
| we transport things - are the fabric on which cities are built.
| Not just inside the cities, but the vast network of roads
| outside the city, that feed it.
|
| Before the 1900s, we weren't able to build cities far from
| water because of their demand for transportation. We can today,
| and it is only because of roads we are able to do that.
| trinari wrote:
| I hope the water comes to the city through a pipe and not
| with trucks on roads.
| fenykep wrote:
| I believe they have referred to the transportation
| possibilities the water allows rather than the possibility
| to transport water (which was possible at scale way
| earlier)
| direwolf20 wrote:
| We finally have water-powered cars?
| rob74 wrote:
| Yeah, maybe I'm overly pedantic, but the author is also
| overly pedantic about the curvatures of streets/roads in
| games, so... :)
|
| But, to continue with the pedantry: the Romans already built
| cities far from (navigable) water. There have been roads
| since antiquity, then since the mid 19th century it was first
| the railways that made it easy to transport passengers and
| goods over large distances. The current version of roads
| being the main/only form of transportation only came about in
| the 1950s.
| spacedcowboy wrote:
| I think American society is very much road-focussed, having
| lived there for a couple of decades. I think UK (and European
| in general) society is very much street-focussed.
|
| A lot of that comes down to geography - the UK is a high-
| density population compared to the USA but the impact on our
| lives is significant. In the US, I would drive everywhere.
| Literally everywhere - to the shops, to the library, to the
| beach, everywhere. Yesterday I took my son to his archery
| practice, we walked along the coast road for about 20
| minutes, and picked up a "Mr Whippy" 99er ice-cream (yes,
| even in the cold weather) along the walk back. It was
| pleasant, and healthier.
| direwolf20 wrote:
| USA cities are low density _because_ they are road-focused
| retired wrote:
| The United States emerged during a period of abundant
| frontier land, which normalized the idea that ordinary
| people could own large, independent plots. This
| contrasted sharply with Europe's older, land-constrained
| settlement patterns. That early culture of space and
| ownership later interacted with industrialization, the
| automobile, and government policy to produce the low-
| density development that characterizes much of the U.S.
| today.
| gwbas1c wrote:
| When you go into the Northeast, a lot of narrower roads
| were planned for slow-moving horse-drawn carts.
| hollerith wrote:
| Horse-drawn carts are not any narrower than cars are, and
| many place (e.g., the Marina District of San Francisco)
| designed in the horse era have very wide streets.
| gwbas1c wrote:
| Pretty much any car that's bigger than a subcompact is
| wider than a horse drawn cart.
| rzwitserloot wrote:
| The vast, _vast_ majority of such infrastructure was turn
| down in the 60s to make way for the almighty automobile.
|
| The number of places in the north american continent that
| retain their street focused infrastructure is pretty much
| countable on one hand, and most of that is being terribly
| managed.
| exhumet wrote:
| Exactly go Worcester, Providence and Boston and be in awe
| at how fucking horrendous the maze is.
| bakies wrote:
| Boston is only horrendous in a car. Walking around and
| taking public transit in Boston is very nice. OTOH
| Providence feels like it's designed for cars, much easier
| to drive there but always need the car around and their
| highways and roads are terrible. There's a ton of highway
| to split the city. Worcester is less highway constricted
| but still definitely need a car to get around and I still
| can't figure my way around.
| dayjaby wrote:
| Another interesting fact about plot sizes in Europe: You
| can see within an area which kind of inheritance law was
| in place: If farming plots are large, usually the oldest
| son inherited everything. If they are small, they were
| evenly distributed.
|
| Source: https://www.sciencedirect.com/science/article/pii
| /S026483772...
| NoboruWataya wrote:
| This may be true, but I think the points made in the
| comment you are responding to are nevertheless true for UK
| and European cities as well. Roads have been a fundamental
| part of the development of modern towns and cities
| throughout the Western world.
| fastasucan wrote:
| >Modern society has an insane demand for transportation.
| Roads - the medium on which we transport things
|
| Why do you say it like roads are the only option? Its even
| far from the most effective option. You mean rails?
| retired wrote:
| Railroads are roads.
| spacechild1 wrote:
| Only by name.
| red-iron-pine wrote:
| rail-roads
|
| is in the name mon ami
| spacechild1 wrote:
| Not in other languages. In German, for example, it would
| very weird to think of railroads
| (Bahn/Eisenbahn/Bahnstrecke) as roads (Strassen). Would
| you also claim that a hedgehog is a pig?
| BobaFloutist wrote:
| But autobahn is a road, no?
| troupo wrote:
| > Modern society has an insane demand for transportation.
| Roads - the medium on which we transport things - are the
| fabric on which cities are built. Not just inside the cities,
| but the vast network of roads outside the city, that feed it.
|
| This is a very American point of view IMO.
|
| Cities are built on streets first and foremost. Otherwise you
| end up with strip malls separated by endless swaths of car
| parks.
|
| As for transportation, we have to separate cargo from people,
| and inner city from inter-city.
|
| For people inside the city you have multi-modal transport
| options. Walking, biking, busses, trams, subways, commuter
| trains, taxis, individual cars, ferries.
|
| For intercity people you have trains, planes, boats, busses,
| individual cars.
|
| Most inner city cargo can be handled by smaller trucks going
| from warehouses to specific places in the city. And for
| smaller cargo like mail I've even seen small scooters and
| cargo bikes.
|
| For inter-city you once again have multi-modal transport
| (depending on the city). Trucks, rail, cargo planes, boats.
|
| Even the US was built on railways, not on roads. Roads are
| the "backbone of cities" only if you make them one, as the US
| has done
| bluGill wrote:
| Slight correction: It was the 1830s when the railroad arrived
| that we started to be able to build cities far from navigable
| water. (navigable is important - if your water can only
| support small boats your city will be smaller than if it can
| support large ships). Trucks in the 1900s allow the same
| thing, and have enough advantages that we would use them for
| smaller cities, but large cities are still going to get rail
| transportation. And water transport is still powerful enough
| that the largest cities still likely need it even though it
| isn't a strict requirement.
| S3verin wrote:
| Roads are important for a good transportation infrastructure.
| However, cities in north america are overreliant on them. In
| European cities public transit is also important and in my
| opinion even more important than roads. Cars are not useful
| in cities compared to public transit / bikes / walking if the
| city is designed for humans and not cars. ( and yes, you
| still need roads for delivery and people who sometimes have
| to transport heavy things).
| bluGill wrote:
| There is a lot more than people to move around a city.
| Transit is more visible and yes europe does well there -
| but freight is less visible and europe isn't doing as well
| there.
| cogman10 wrote:
| > Before the 1900s, we weren't able to build cities far from
| water because of their demand for transportation.
|
| Incorrect.
|
| In the 1800s the train took off as a primary form of
| transportation. By 1869, we'd completed the first
| intercontinental railway in the US which ultimately opened up
| the economy between the east and west.
|
| Sears flourished as a company because of the train.
|
| It wasn't roads which ultimately opened up mass transport, it
| was rail. It wasn't until the 1950s that rail was ultimately
| de-prioritized and roads were prioritized.
| flomo wrote:
| I will just say the _Streets of San Francisco_ were almost all
| built by civil engineering principles, even those from the 19th
| century. If you want some sim SF or NYC, this guy is on the
| right track by not having fakey roads.
| Ef996 wrote:
| Yep, good point. I am myself a huge fan of livable oriented
| infrastructure (bike lanes, pedestrian paths, public
| transportation) but the hard truth is that roads were initially
| designed for carriages and later for cars. A though I
| recurrently have is how would a city designed from scratch by a
| civilization that uses only bikes and walking look like?
| vladms wrote:
| Why should you use only bikes and walking? Cars/trucks have a
| role to play, it's just not the most efficient to move the
| majority of the people from one point to another. Simple
| examples: ambulances, firefighters, police, cranes.
| Ef996 wrote:
| True. I mostly meant not personal vehicles, so jut buses,
| trams etc. I supposed emergency services will use those
| dedicated lanes. or maybe civilization is so advanced those
| will be served via flying only. Idk just since fiction
| thinking.
| wongarsu wrote:
| The same insights still hold true for streets and paths. Of
| course a single human or even bicycle can move with fewer
| constraints than a car, but a stream of humans won't. When we
| design pedestrian infrastructure with sharp corners people
| either cut through on the inside, creating desire paths on
| unpaved surface, or the inside section that lies on the paved
| path but outside the circle-section-path becomes a low-traffic
| zone, a place where people sit down or put up food carts or
| whatever
|
| In remembering that cities are not roads alone, but also
| streets, paths and tracks, there is a lot of potential for this
| approach to building all of them
| BrtByte wrote:
| Urban planners lose sleep over stroads for very good reasons
| but from a simulation and tooling perspective, streets still
| need a shared geometric backbone
| laci37 wrote:
| I don't think that much is shared between streets and roads.
| Roads need all the details about curvature in the article so
| car traffic flows efficiently. Compare that to the beautiful
| but narrow streets of a Mediterranean town. Buildings are
| rarely parallel, angles are odd, but everything is on a human
| scale, and it just feels good to walk around.
| voodooEntity wrote:
| Always thought some streets in city builders just are a bit
| tooooo off :D
|
| Very nice article - good read !
| spacedcowboy wrote:
| Bezier curves - specifically for things like roads where you want
| a single definition of the road/path and an extended image that
| obeys that path, turning it into a pair of offset-beziers aren't
| the easiest thing to work with. They collapse to a visually
| unattractive solution at extreme boundary conditions (such as a
| tight turn)
|
| You can see it in one of his examples where the bezier curve has
| an inflexion point which crosses over itself on a sharp bend. I
| ran into this while writing Azoth [1] last year, when wanting to
| be able to overlay paths with blending into the background at the
| sides, and curving around existing features on a game map. To
| solve the problem, I simplified it, and there's an (animated)
| example of how I got it working here [2]
|
| [1] https://github.com/ThrudTheBarbarian/Azoth
|
| [2]
| https://github.com/ThrudTheBarbarian/Azoth/blob/main/Documen...
| sam_lowry_ wrote:
| At some point I Google Maps was using Bezier curves for roads,
| but then they started approximating even roundabouts with
| polylines, and this looks unbelievably clunky.
|
| Some manager at Google should have gotten an appraisal for
| removing proper curves from Maps, because... who cares, they do
| not need them on US streets.
| ChicagoDave wrote:
| Now imagine a city where there is no human driven transport:
| pedestrians, bicyclists, and automated vehicles exist in
| different constructs above and below ground and never cross each
| other's path completely negating the inherent risks. No roads. No
| parking. Just fluid, cohesive movement.
| xixixao wrote:
| I've been kinda obsessed with getting clothoids to work in a
| railway track editor. It's easy enough to build out of clothoids
| into empty space, but connecting tracks is where it gets really
| hard.
|
| For now all I have to share is this explainer I made some years
| ago: https://xixixao.github.io/euler-spiral-explanation/
| Ef996 wrote:
| Wow, that's a really detailed deep dive, saved it for a read
| later. I didn't even realize clothoids are also tricky to
| connect. I never really dared to jump into actually
| implementing them myself.
| noduerme wrote:
| Super dumb question but if you have one railway line on the
| left splitting into two on the right: if you extended the
| clothoids of the two back to the left past the junction, would
| their wave patterns intersect each other again? What happens if
| you take the further left cross intersections and then split to
| the right from there along bezier curves to two points matching
| the x+ of the original intersection and an arbitrary y-/y+
| where the further-back (left) waves intersected? Purely
| spitballing but is there a way you could use the previous two
| points where the ripples crossed before the point of the
| junction, and interpolate splines from there?
|
| Bad/quick visual: https://pasteboard.co/5QgDdTVVSm1I.png
| interloxia wrote:
| In my next game, Canalpunk, I'm planning to keep with bezier
| splines. The self intersection of the paths will make the
| disaster system more interesting.
| e2319685 wrote:
| Daniel
| vanaur wrote:
| One may also be interested in Egregoria
| (https://github.com/Uriopass/Egregoria). This is a 3D city
| builder written in Rust, with particular attention to roads. I
| have never used the project (because it would not be useful for
| what I usually do), but I have been following its development at
| the beginning and I think it is quite cool stuff.
| cookiengineer wrote:
| As a German, pretty much all of the intersections shown in the
| article trigger me quite a bit. In Germany, there's a
| standardized Autobahnkreuz [1] most of the time. If it's a
| construction site or an incompleted Autobahn intersection, it's
| usually called Autobahndreieck (and not -kreuz) on the signs.
|
| This way, all drivers can already sort themselves onto the
| matching lanes without even having seen the signs yet.
|
| The standardized Autobahnkreuz also has always identical ways to
| change directions, where the left lane leaving the highway is
| made for change in opposite direction or for turnarounds. So if
| you took the wrong exit, you can always save yourself by just
| driving that lane 3 times across the bridge.
|
| If the traffic increases over time, usually the right exit lanes
| are doubled and that fixes the problem.
|
| Rarely though there's different setups like around the A61 and
| A67 where the traffic around and towards Frankfurt city / airport
| is too huge for that system.
|
| [1] https://de.wikipedia.org/wiki/Autobahnkreuz
| lstodd wrote:
| MKAD, the 101km circle road around Moscow had almost
| exclusively this style of intersections up until 2010s, when
| congestion got absolutely unbearable. Then all of them got
| rebuilt, typically adding overhead ramps, tunnels, and crazy-
| long but separate right lines, and by now it's almost
| impossible to navigate w/o gps navigator (which gets jammed
| often). Also forget about easily changing direction.
|
| Results can be seen on f.ex
| https://www.openstreetmap.org/#map=16/55.88242/37.72732
| cookiengineer wrote:
| Damn, this is pretty interesting that they had to add the
| additional bridges.
|
| Does that imply that the merge of two lanes is still too
| costly?
|
| Also it seems the lane from south east to south west is
| missing :D it's somehow routed via north first and then goes
| around the circle.
| lstodd wrote:
| > Does that imply that the merge of two lanes is still too
| costly?
|
| Yes.
|
| This one
| https://www.openstreetmap.org/#map=16/55.88495/37.47959 was
| built from scratch not very long ago. Notice how
| merges/splits are spread as far as possible.
| Notatheist wrote:
| In my early days someone told me generating roads is a non-
| trivial problem and I thought that was bollocks so I spent 4
| months smashing my head against a wall to prove them wrong!
|
| >A clothoid gradually increases curvature over distance.
|
| This seems complete overkill? I remember smoothing between
| tangents of two circles to mostly solve roundabouts. I had to
| cheat for 3+ lane roundabouts but it worked for any semi-
| realistic road.
|
| >Just simple rules stacking on each other that result in
| beautiful patterns. I can't explain why, but seeing those
| structures always felt good.
|
| I think in 2026 it's safe to blame your autism. I do. Nobody
| likes Factorio because it's a good game. We're here for the lines
| and grids.
| austin-cheney wrote:
| I have never seen a Texas style mixmaster, or stack exchange, in
| a game. Here is an irregular example:
|
| https://en.wikipedia.org/wiki/Spaghetti_Junction
| pixl97 wrote:
| I think one of the reasons is space. Games tend to pack things
| in a pretty dense interface, quite often because it seems more
| exciting that way, and keeps the map size reasonable.
|
| These things are absolutely huge pieces of infrastructure that
| can take the space of dozens to hundreds of buildings.
| BrtByte wrote:
| Nope, most players won't consciously care but systems built on
| the right constraints tend to feel right even when you don't know
| why
| lloeki wrote:
| "if it looks good, it flies good" (or s/good/right/g) is an old
| aviation adage about aircraft
|
| https://m.youtube.com/watch?v=PG4gr0Q4904
| Ahnonimus wrote:
| Minecraft
| ramonga wrote:
| If you liked this you'll love playing mini motorways (available
| in many platforms including mobile/ipad)
| curiousObject wrote:
| This is interesting, I look forward to reading more. But I think
| it's wrong, if you want to represent reality.
|
| Real cities were all built in the past, for older vehicles, which
| moved at different speeds, and were controlled by drivers with
| different goals from today's drivers.
|
| So, if your game has bad and unsafe road designs, which have been
| partly retrofitted to reduce the worst problems, _then that is
| accurate_.
|
| A game with optimal roads is not an accurate simulation of
| reality.
|
| A professional modern road designer will simulate the expected
| movement of vehicles through a new or redesigned road, to try to
| discover major problems.
|
| They look for problems with turning radius, visibility, stopping
| distances, and interactions with other road users.
|
| I believe that a game designer could offer to do the same.
|
| The game could draw a good algorithmic road shape first. But next
| offer the player an option to run a simulation of individual
| traffic movements, to discover serious issues, and let the player
| know about problems.
|
| To the OP, I suggest this simulation approach, not trying to
| discover flawless algorithms. That's not how it happens in the
| real world.
|
| Several comments have suggested similar issues.
| nkrisc wrote:
| That sounds more like a traffic simulation tool rather than a
| game.
| pixl97 wrote:
| Simulation games are very popular these days.
| tgtweak wrote:
| Cool - now make it into a mod for cities skyline :)
| JKCalhoun wrote:
| Love these deep dives--perfect HN fodder. Add to that articles
| like this also on the front page today: "Algorithmically Finding
| the Longest Line of Sight on Earth," "Tesselation Kit"...
|
| HN, keep being HN! We love you.
| devnullbrain wrote:
| >You see, the shapes of roads in real life come from an
| underlying essential fact: the wheel axles of a vehicle. No
| matter how you drive a car, the distance between the left and
| right wheels remains constant. You can notice this in tyre tracks
| in snow or sand. _Two perfectly parallel paths_ , always the same
| distance apart _maintaining a consistent curved shape_.
|
| Emphasis mine - that's not really true
|
| - Cars have differentials, so the wheel speed can differ between
| wheels
|
| - Steering geometry isn't parallel! The tyres turn a different
| amount when you turn the wheel
|
| - Unless you're going in a straight line, cars don't go where the
| tyres point! Tyres 'pull' the car towards their slip angle
|
| What you will actually see in tracks in snow or sand is non-
| parallel tracks, describing curves of different radii. You can
| also see this in racetracks, where the path more closely
| resembles the limits of car physics without care for passenger
| comfort or tyre wear. The example 'fail' image looks not
| dissimilar from a hairpin turn.
| iggldiggl wrote:
| See https://www.thecontactpatch.com/ for some interesting
| reading material related to that.
| JackFr wrote:
| Railroad cars don't have differentials and travel on parallel
| tracks. How?
|
| https://www.reddit.com/r/Skookum/comments/47sbri/richard_fey...
| pixl97 wrote:
| For those that don't read the link, by having conical wheels.
| Ef996 wrote:
| Author here: i agree the article oversimplified here and in
| practice vehicle tracks can sometimes be non concentric. But it
| has nothing to do with differentials. Differentials just allow
| wheels to rotate at different speeds (as perimeter of a smaller
| radius circle is smaller the outer one). Non parallelism
| usually comes from the Ackerman steering or slipping. But rear
| tracks of a vehicle going slowly through sand will always be
| concentric. Parallelism is important for engineers because it
| also allows multiple vehicles to go in parallel on a multi lane
| road. You can see how that is failing with bezier paths in the
| CS2 ss in the article. Also hairpin turns are usually designed
| with arcs in mind as well
| frou_dh wrote:
| In 3D games, something that's key for roads to look/feel
| realistic is to have small amounts of banking here and there all
| over the place - as opposed to just having a crude categorisation
| where there are flat roads on one hand and ramps on the other.
|
| If you don't do that then large parts of the game world end up
| seeming like ice rinks with roads painted on them.
| dandellion wrote:
| Not just roads! I made a small train game for a game jam, and I
| used splines for the tracks to get them done quickly. It did the
| job, but they looked wrong to me. So I revisited it a few weeks
| later and looked into arcs and clothoids as well. I replaced the
| splines with some basic code using arc and the result looked so
| much better.
| adamrezich wrote:
| Very disappointed that this article ends just before it starts to
| get into anything concrete and interesting--I'm working on
| solving (a simplified subset of) very similar problems for a game
| I'm working on, and would love to learn more about the author's
| approach!
| pixl97 wrote:
| >Does everything I just rambled about matter? Do 99% of city-
| builder players care what shape the corner radius of the
| intersection has? Most likely, no. Then why bother?
|
| To me, yes, then again I may end up with a basement full of model
| trains when I'm old.
|
| Still annoys me to no end when the game model builds something
| unrealistic and would be an absolute traffic nightmare in the
| real world.
| jet98 wrote:
| Streets ahead
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