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Show HN: Algorithmically Finding the Longest Line of Sight on Earth
We're Tom and Ryan and we teamed up to build an algorithm with Rust and SIMD to exhaustively search for the longest line of sight on the planet. We can confirm that a previously speculated view between Pik Dankova in Kyrgyzstan and the Hindu Kush in China is indeed the longest, at 530km.
We go into all the details at https://alltheviews.world
And there's an interactive map with over 1 billion longest lines, covering the whole world at https://map.alltheviews.world Just click on any point and it'll load its longest line of sight.
Some of you may remember Tom's post[1] from a few months ago about how to efficiently pack visibility tiles for computing the entire planet. Well now it's done. The compute run itself took 100s of AMD Turin cores, 100s of GBs of RAM, a few TBs of disk and 2 days of constant runtime on multiple machines.
If you are interested in the technical details, Ryan and I have written extensively about the algorithm and pipeline that got us here:
* Tom's blog post: https://tombh.co.uk/longest-line-of-sight
* Ryan's technical breakdown: https://ryan.berge.rs/posts/total-viewshed-algorithm
This was a labor of love and we hope it inspires you both technically and naturally, to get you out seeing some of these vast views for yourselves!
Hi Tom it's Marc, I'm glad to see you finished your sightline project ! Any clue why you report the longest sightline as "530.8 km" when it seems to be actually 538.1 km? That's what my code calculated (https://news.ycombinator.com/item?id=45512970) that's what Dr. Ulrich Deuschle also calculates (https://www.udeuschle.de/panoramas/panqueryfull.aspx?mode=ne...) You, Deuschle, and I all use the same DEM data (https://www.viewfinderpanoramas.org/Coverage%20map%20viewfin...) and the same refraction coeff (0.13), and nearly the same camera height (1.5m for me, 2.0m for Deuschle, and 1.65m for you—and these heights make almost no difference). Something must be slighly off in your computations? Or do you think both Deuschle and I are wrong?
Cool project! Unfortunately our planet has this pesky (but very useful!) thing called atmosphere, which makes all these extra-long lines of sight only theoretical, I guess? Ok, the longest line of sight is mostly over the Taklamakan desert, so probably very dry air (which might however have some dust/sand in it), but still?
Thanks!
Well the record for the longest photographed line of sight is in the same region as our #3 longest line, at 483km https://www.guinnessworldrecords.com/world-records/66661-lon... So not far off. And I think that even takes advantage of some favourable refraction. So not only might it be possible to see the longest view. But there may even be longer lines if we were to take into account extreme cases of refraction. Which is certainly something we'd love to try.
Wow, that's an impressive amount of dedication, but I guess you need that if you want to set a world record:
> He monitored weather conditions closely to find the right window and right location. After a lot of travelling he arrived at Aksu village. The village wasn't accessible by car due to snow and ice so he hiked to the summit. After 10 hours of climbing, he stood on the summit with moonlight providing enough light to set up his equipment. At midnight, he recalls that the temperature was around -12°C with winds around 8 m/s. He remained there all night capturing panoramic photos. Before sunrise, the wind picked up to roughly 20-25 m/s and the battle of capturing his world record image began. He planned to capture the image at sunrise to improve contrast and whilst he is pleased with the final result, he is already making plans for his next record-breaking image.
But still, that kinda confirms my observation about the pesky atmosphere: even with optimal weather conditions, he still needed the sun lighting up the sky behind the mountains just before sunrise, otherwise they would have blended in with the sky at the horizon...
This also applies for much shorter distances: despite what the publicity photos suggest, you can't see the Alps from Munich most of the time (or only as slightly darker shapes on the horizon), although they're "only" ~ 75 km away. You need really good weather to see them clearly...
> This also applies for much shorter distances: despite what the publicity photos suggest, you can't see the Alps from Munich most of the time (or only as slightly darker shapes on the horizon)
You won't usually see them from the ground of course but from a couple floors up with a clear line of sight you do see them quite often.
Putting on my pedantic hat, does this qualify as a picture of the mountains? As in, is there any light hitting the mountains, then hitting the film/sensor?
Or is this just an elaborate silhouette?
Is that a difference? I don't know.
Its a really interesting question.
Lets take it to its farthest extent: can you take a picture of a black hole?
> Wow, that's an impressive amount of dedication, but I guess you need that if you want to set a world record
Dedication, mmm, dedication. dDdication, that’s what you need. If you want to be the best, and if you want to beat the rest. Dedication way you need.
Hopefully that means something to Brits of a certain age ;-)
Roy Castle!
Do the two points have to be on land? I would think since you can see the ocean from Aconcagua you'd be able to see all the way to the horizon and that would be the longest sightline
funny to know that the record has just been broken, the latest I knew of was by Roberto Antezana, astrophotographer from Universidad de Chile, capturing the Aconcagua (6950m) peak from Cordoba, Argentina, taking advantage of the peak's altitude and the Argentinian pampa (very flat grasslands), and of course, thorough planning + lucky cooperative weather [1] [2]; he was well known before from his long distance photos of the same peak from Valparaiso bay [3], I'm from Valparaiso and the times it was possible to see that peak with the naked eye given some perfect blue sky was truly overwhelming, since then I've been thinking about how to achieve such excursion planning heuristically from topographical data available. Congratulations on your project, I will look more into the technical details but looks amazing, beautiful art and technique!
[1] https://uchile.cl/noticias/205455/astrofotografo-logra-nuevo... [2] https://dalekiewidoki.pl/2025/07/world-record-andes.html [3] https://api.flickr.com/photos/robertoantezana/4994301227/
ok then, If I read you right, what counts is someone going and doing the actual seeing , VS drawing a line on a topigraphical map. there are groups on another quest flying gliders into the high stratospher riding atmospheric waves rolling up against mountains who might also qualify for setting records for the longest possible views through the atmosphear, they got started buying surplus soviet space suits as that was what made attempts possible.
I tried the summit of Mt Ruapehu here in NZ and got 358.8 km to Mt Owen. Not bad as I was expecting Tapuae-o-Uenuku which is a little shorter at 342 km.
One advantage in NZ is that on a nice day you actually have a good chance of seeing it.
Oh ... clicking on Mt Owen doesn't return the favour ... or the other nearest peaks. But Culliford Hill does show a return back to Ruapehu, 355.4 km. Clicking on Tapuae-o-Uenuku also, as expected, gives a line to Ruapehu: 342.3km.
Mt Cook is high, but has too many other high peaks near it.
Mt Taranaki is isolated, but doesn't turn up any very long distances.
I don't expect any other candidates in NZ.
Update: actual and accidental photo of Tapuae-o-Uenuku from Ruapehu (342 km), seven months ago.
https://www.reddit.com/r/newzealand/comments/1m9p0bh/tapuaeo...
And, as pointed out in a comment, also Mount Alarm 2.5 km further.
What is the longest in North America? Or Europe proper -- not Elbrus (which I've not been to but have been close enough to see, from several places e.g. from a house in Lermontov (~94 km only), summit of Beshtau (93 km), Dombai ski field (~63 km), somewhere on A157 (~50km).
Wow, glad you had fun exploring. It suddenly made me think of a little feature that I'm not sure we made the best job of exposing. In the little trophy icon toggle on the right, there's the Top Ten list of views, then under those there's a little line that just says "In current viewport: 123km". Did you see that? Did it make sense? I implemented it, so of course I know that it's better than clicking all the points around a peak to find the longest view from a mountain summit. But maybe it's not obvious to other users? What I do is zoom in so that the viewport only contains the area of the summit (or indeed entire country for that matter) that I'm interested in, then I look at that "In current viewport:" line without having to click anything.
So using that, I would say that the longest line of sight in North America is from Mount Rainier, at 390km, looking North West into Canada: https://map.alltheviews.world/longest/-121.76853942871094_46...
Oh, I missed that!
That gives a longest in NZ of 365.3 km from Ruapehu, skirting past close by Tapuae-o-Uenuku (in the Inland Kaikoura Range) to a point on the Seaward Kaikoura Range near the peak of Manakau. Clicking on the actual Manakau peak also gives 365.3 km back to Ruapehu.
I can't seem to find a peak to get a reverse path back to Mt Ranier. Everything I try gets stuck in the Olympic Peninsular. (I was there once ... 1998 or so ... a place called Hurricane Ridge IIRC)
Right, I think we need to make that "In current viewport" thing more prominent somehow.
So this is the NZ longest line right https://map.alltheviews.world/longest/173.61386108398438_-42...
One thing to note about finding reverse lines, is that they're not truly mathematically identical because the observer always has a height of 1.65m and the destination is always some point at the surface, therefore 0.0m. It doesn't always make a difference, but it sometimes can.
Not a geologist, but interesting that many of these sites are close to equator. Suppose that's where mountains are higher because tectonic plates are more active?
Anyone with expertise want to comment?
Not a geologist either but an astronomer. Never heard that tectonic activity has any association with proximity to equator.
Mountains can rise higher near equator because you have the least gravity there. The whole Earth bulges along the equator. But I don't think it's measurable.
It's also interesting because the radius of curvature is smaller, meaning the distance to the horizon is shorter north south, and a lot of these views are north south. So the increase in mountain height more than overcomes the other effect!
Woah, I've been thinking about this whole project for so long, but never considered that!
While Everest (8849m) is the highest point above Sea Level, Chimborazo (6267m) in Ecuador is further from the centre of the Earth (about 2000 metres further), due to the equatorial bulge. It's very measurable.
The website claims the longest line of sight in my city is 24.7km from someone's garden that is surrounded by houses. I walk past this particular spot on my way to the gym. I walk downhill from my house to get there. I seriously question the reliability of this data.
The resolution of the underlying data is only ~100m. So most houses, vegetation, etc, gets blurred into the same smooth surface. There are actually higher resolution data sets, even up to centimetre scale, using LiDAR, of cities. We'd love to integrate these but it's a few orders of magnitude more data.
Neat. I did a related project a little while ago. I wasn't interested in how far I can see from everywhere, so much as what I can see from one place in particular.
So in mine you can click on a spot and it draws black lines over any land that is occluded by terrain, within 100km.
(But all with AI-generated JavaScript, not cool Rust and SIMD stuff)
https://incoherency.co.uk/line-of-sight-map/
I am not sure if I'm experiencing what you describe. I just see a radiating circle of black lines, no matter where I click. I decided to click a local, notable "long line" viewpoint -- Lick Observatory outside San Jose. From here, on a clear day, you can see Half Dome in Yosemite, 120mi away. I still just see a black circle.
Are you standing on a raised platform when you see the Half Dome?
This is what I get when I set the observer height to 20m, and increase the "max distance" to 300km (200km = ~124 miles so may not be enough).
https://img.incoherency.co.uk/6478
It's also possible that the half dome is too short and the sampling rate of the line-of-sight jumps over it!
It seems that sometimes it fails to load the height map, try reloading the page. You should see terrain shading if it's loaded properly.
I think the lines indicate areas that you can't see?
It's buggy. Mission peak shows much of the bay area occluded.
> But all with AI-generated JavaScript, not cool Rust and SIMD stuff
Heh, I almost hit back at the "in Rust" mention.
Would the end result have been different if it were done in python calling C libraries for performance? I strongly doubt it.
There was a post here about 6 years ago for a site that calculated line of site for any two points on a map with both the max line of sight and 2D cross sectional view of the terrain difference between the two points. I haven't been able to find it since 2020, but it was awesome.
Could it be this? https://www.udeuschle.de/panoramas/makepanoramas.htm
No, it used a much heavier JS interface and IIRC it also used Google Earth. That is a nice tool, thanks for sharing it.
Since you have the data could you show how far you can see in every direction rather than the longest direction?
Yes, but, there's one small problem, storing this extra data for the whole world starts to run into the petabytes!
This would be incredible - please add this!
Cool places to try wifi long shots.
I did some longshots back in the early days of wifi.
You'd need to do a bit of work to adjust the timing, I suspect. At 530km the time delay would be around 1.75ms which would be enough to greatly upset WiFi ;-)
You could probably talk between ends using cheap crappy 446MHz 250mW walkie-talkies though.
This data base could be used to optimally place meshtastic nodes.
You could just send raw 802.11 data frames and then receive them with monitor mode on the other end.
This is so interesting. Thanks for sharing. I have been working on a similar project where instead of finding all the sights I have focused on finding all the cycling climbs in the world. I think there is a sense of satisfaction in finding ALL of something.
Cheers
www.climbs.cc
how close is this to the theoretical maximum?
if we put mt. everest on a sperical cow, i mean on a planet with only ocean, how far could you see there? how far away could a second peak of the same height be, before it gets hidden by the curvature of the planet?
If we have a 9 km mountain on an otherwise spherical planet (r=6371 km), the horizon would be 339 km away. With two mountains having a sightline between eachother the maximum theorethical distance doubles to 678 km.
Exactly.
And it could even be tweaked slightly with some favourable refraction.
This is the geography I was promised in school
I mean this is coming to the same result as heywhatsthat, apparently using the same dataset. Sadly it is not really correct, in that I think it blends a lot of things, including TREEs into the height. Its very obvious many places that some height is just not true, unless you account for buildings and treetops.
I believe I _might_ have a 33km view FROM MY ROOF, from 2m above ground I have much less than 1 km.
Hopefully this won't become a tool for the Flat Earthers. =)
Might be a tool against them. Note that Mt. Everest isn't on the list. If the Earth was flat, all the tallest peaks would be seeable from one another unless a specific peak taller than one of them was exactly in the way.
We're actually thinking of writing a SIGBOVIK paper where we explore running this whole thing for a Flat Earth!
It's wild in the upper midwest you can SEE the glacial effects on the terrain better than any topo map I've seen before.
I was wondering that too, that this might be a better visualisation of certain geological features. But I don't have much experience, so can't say for sure.
It's a sort of high-pass filter I guess? Using the curvature of the earth to highlight local changes in elevation.
This is my favourite kind of HN post, and I absolutely love this one. Would love to see photos from each of these views.
I was looking for those on the website. Maybe we could find some photos on Google Maps that already exist from these locations.
Thank you <3
Well there is a photo near our #3 longest line of sight https://www.guinnessworldrecords.com/world-records/66661-lon...
It be nice to get the 3 or 5 longest distances from a specific point, not just the longestest
Claps!