9 ms·

Show HN: Algorithmically finding the longest line of sight on Earth

412 points by tombh 8mo ago

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 https://alltheviews.world And there's an interactive map with over 1 billion longest lines, covering the whole world at https://map.alltheviews.world 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 https://tombh.co.uk/longest-line-of-sight * Ryan's technical breakdown: https://ryan.berge.rs/posts/total-viewshed-algorithm 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! 1. https://news.ycombinator.com/item?id=45485227 https://news.ycombinator.com/item?id=45485227

umpriel 8mo ago
Claps!
- ryanbberger 8mo ago
  Thanks umpriel for the PR, hope you're well!
zoobab 8mo ago
Cool places to try wifi long shots. I did some longshots back in the early days of wifi.
- ErroneousBosh 8mo ago
  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.
  - galangalalgol 8mo ago
    This data base could be used to optimally place meshtastic nodes.
  - 1e1a 8mo ago
    You could just send raw 802.11 data frames and then receive them with monitor mode on the other end.
    - ErroneousBosh 8mo ago
      If I had just re-read Neal Stephenson's Cryptonomicon recently, which I have, I'd say that I'd set up a link using WEP-encrypted 802.11b and hammer data across it with odd little bits here and there designed to generate maximum spy interest. But then the actual message would be encoded by very slightly favouring the high or low end of the spread spectrum map as a kind of terribly slow FSK.
  - zoobab 8mo ago
    For longshots, there was a value called "ack_timeout" that you needed to tune: https://gitlab.com/nsnam/ns-3-dev/-/issues/41 https://gitlab.com/nsnam/ns-3-dev/-/issues/41
jstanley 8mo ago
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/ https://incoherency.co.uk/line-of-sight-map/
- eitally 8mo ago
  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.
  - arethuza 8mo ago
    I think the lines indicate areas that you can't see?
    - jychang 8mo ago
      It's buggy. Mission peak shows much of the bay area occluded.
  - jstanley 8mo ago
    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 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!
  - 1e1a 8mo ago
    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.
rob74 8mo ago
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?
- tombh 8mo ago
  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-longest-line-of-sight-on-earth 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.
  - rob74 8mo ago
    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...
danielsamuels 8mo ago
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.
- tombh 8mo ago
  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.
- DiggyJohnson 8mo ago
  I think you're assuming more fidelity than the project is claiming
  - danielsamuels 8mo ago
    I'm assuming that when the project says you can see 24 km from a given location, that you can see 24 km from that location. That's not the case. Fundamentally, it doesn't do what it claims to do. Why allow the user to select any arbitrary location on a map and give an answer when you know the answer is most likely nonsense? You don't need to compute for 2 days to accomplish that; you could just make it up.
    - crazygringo 8mo ago
      Surely you understand it's based on limited resolution data, and therefore intended to be used at the scale of general topography like mountains and valleys? That it's not taking into account human construction or distances of tens of meters? Presumably you can walk a little bit and climb on someone's roof to see the claimed 24.7 km. Assuming a sufficiently clear atmosphere, and that there isn't a tall office building in the way or something.
    - wat10000 8mo ago
brucehoult 8mo ago
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/tapuaeoueneku_kaikoura_ranges_captured_from_the/ 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).
- repelsteeltje 8mo ago
  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?
  - kmaitreys 8mo ago
    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.
    - jmalicki 8mo ago
      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!
alvsilvao 8mo ago
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
ourmandave 8mo ago
Hopefully this won't become a tool for the Flat Earthers. =)
- emiliobumachar 8mo ago
  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.
- tombh 8mo ago
  We're actually thinking of writing a SIGBOVIK paper where we explore running this whole thing for a Flat Earth!
pestatije 8mo ago
It be nice to get the 3 or 5 longest distances from a specific point, not just the longestest
- tombh 8mo ago
  It's just a matter of storage costs. Even storing a single line of sight for every point on the planet is over 200GB!
noosphr 8mo ago
Since you have the data could you show how far you can see in every direction rather than the longest direction?
- bartread 8mo ago
  This would be incredible - please add this!
- tombh 8mo ago
  Yes, but, there's one small problem, storing this extra data for the whole world starts to run into the petabytes!
  - em-bee 8mo ago
    what if you put a limit on it? like only a dozen views per point, and only views that are at least 100km. or only do this for peaks or points of interest. or some combination like more views for higher peaks, less for lower ones.
    - tombh 8mo ago
      Ohh yes, nice ideas.
      - em-bee 8mo ago
        i don't know if that makes sense but it could be interesting to split the views of any point into multiple segments, and then for each segment find the largest distance. next between two of these largest views find the shortest view. if the ends of each view are connected by lines the result would be a zigzag circle around the starting point that gives you a rough idea of the visible area. most points would be on a slope so they would just have a half circle, only peaks themselves would have an all around view.
drcongo 8mo ago
This is my favourite kind of HN post, and I absolutely love this one. Would love to see photos from each of these views.
- tombh 8mo ago
  Thank you <3 Well there is a photo near our #3 longest line of sight https://www.guinnessworldrecords.com/world-records/66661-longest-line-of-sight-on-earth https://www.guinnessworldrecords.com/world-records/66661-lon...
- venusenvy47 8mo ago
  I was looking for those on the website. Maybe we could find some photos on Google Maps that already exist from these locations.
em-bee 8mo ago
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?
- laci37 8mo ago
  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.
  - tombh 8mo ago
    Exactly. And it could even be tweaked slightly with some favourable refraction.
    - stockresearcher 8mo ago
      Ah, well NASA left some mirrors on the surface of the moon so with some favorable reflection and infinite quality optics, you can theoretically see halfway around the world.
alansaber 8mo ago
This is the geography I was promised in school
1970-01-01 8mo ago
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.
- tombh 8mo ago
  Could it be this? https://www.udeuschle.de/panoramas/makepanoramas.htm https://www.udeuschle.de/panoramas/makepanoramas.htm
  - 1970-01-01 8mo ago
    No, it used a much heavier JS interface and IIRC it also used Google Earth. That is a nice tool, thanks for sharing it.
- sandos 8mo ago
  heywhatsthat?
  - 1970-01-01 8mo ago
    I think that was it, thank you for finding it again! Actually, I was thinking of https://caltopo.com/map.html https://caltopo.com/map.html but your site led me to it.
- 1970-01-01 8mo ago
  It was https://caltopo.com/ https://caltopo.com/ https://www.heywhatsthat.com/ https://www.heywhatsthat.com/ is another bookmark that I had lost to time.
colechristensen 8mo ago
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.
- tombh 8mo ago
  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.
  - colechristensen 8mo ago
    It's a sort of high-pass filter I guess? Using the curvature of the earth to highlight local changes in elevation.
    - tombh 8mo ago
      I'm not that familiar with high-pass filters. But yes it's the way it exposes local changes in elevation that is unique. Indeed the heatmap is generated dynamically for every change to the zoom and viewport.
sandos 8mo ago
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.
mrb 8mo ago
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 https://news.ycombinator.com/item?id=45512970) that's what Dr. Ulrich Deuschle also calculates (https://www.udeuschle.de/panoramas/panqueryfull.aspx?mode=newstandard&data=lon:77.684167$$$lat:41.059167$$$alt:auto$$$altcam:2$$$hialt:false$$$resolution:600$$$azimut:169.7$$$sweep:1$$$leftbound:169.2$$$rightbound:170.2$$$split:2$$$splitnr:1$$$tilt:-2.14166666666667$$$tiltsplit:false$$$elexagg:1$$$range:750$$$colorcoding:false$$$colorcodinglimit:493$$$title:Pik+Dankova$$$description:$$$email:$$$language:ge$$$screenwidth:2560$$$screenheight:1414 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%20viewfinderpanoramas_org3.htm 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 differing heights make no difference given the coarse DEM resolution). Something must be slighly off in your computations? Or do you think both Deuschle and I are wrong? Edit: to be clear the difference stems from our coordinates. Our starting points are: 41.059167,77.683333 (me) 41.0181,77.6708 (you) And our end points are: 36.295364,78.755593 (me) 36.314,78.7654 (you) Also I calculate the distance assuming the Earth is spherical (which gives 538 km) not the standard geodesic (which would give 537 km). And in the DEM data I measure the distance from the center of a cell to another (not the edge), while measuring from edge to edge may explain a difference of at most 0.1 km as the DEM resolution is 3 arcseconds. So clearly we disagree on the coordinates of the exact actual sightline as we have a 7 km difference :-) Edit #2: clearly the error is on your side. I should have checked this first, but the coordinates you give for the "To" point (41.0181,77.6708) land in a valley with the south view completely blocked so it's impossible to view 500+ km south as you claim. Look at where the marker lands on this Google Maps Terrain: https://maps.app.goo.gl/PgBWxi31WZC6vk3V9 https://maps.app.goo.gl/PgBWxi31WZC6vk3V9
- ryanbberger 8mo ago
  Hey Marc, Ryan here. Tom may respond as well There's two forms of interpolation going on here that I'm not sure you or Dr Dueschle are using. We interpolate a "band of sight" of single a degree for our azithmual projection, but uniquely we also rotate the DEM elevations around all the observers rather than the observer around to see all the elevations. The effects of the first can be lessened by lowering the band of sight such that we only process half a degree at a time so that we make sure we get more coverage further away. We plan on running some more experiments by rotating to cover more points. The algorithm is already fairly expensive to run against the whole world so we weren't particularly interested in that level of coverage for the full earth. For total viewshed area, our algorithm comes in at roughly a percent or so difference which was what we used as our benchmark for correctness. All this to say, no, we don't think you both are wrong, we've been looking at making ours more accurate. At a world scale that's quite computationally expensive, so we didn't use that methodology for our initial launch. We see our results as validation of yours, not as something we've disproved. Edit: grammar
IshKebab 8mo ago
Can you actually see anything in real life though?
- tombh 8mo ago
  The longest and second longest haven't been photographed yet, but #3 has https://www.guinnessworldrecords.com/world-records/66661-longest-line-of-sight-on-earth https://www.guinnessworldrecords.com/world-records/66661-lon...
amingilani 8mo ago
Now we just need to put two hams with 2m/70cm radios to make the longest line-of-sight QSO on the planet. Bonus points for QRP. Definitions: * Hams: Amateur radio operators. * QSO: conversation or contact between two radio stations. * QRP: Low power, typically under 5 watts.
- tombh 8mo ago
  That's actually one of the legitimate uses cases we've consider for the algorithm.
  - stilldavid 8mo ago
    This is so rad! Here's a photo of me making a 1.2Ghz FM contact 244km away from the summit of a 14er to the summit of another 14er here in Colorado. That particular band is very line-of-sight, with not much propagation or reflections like even 2m SSB or the HF bands. This is a very fun tool that I can't wait to explore more! https://www.k0nr.com/wordpress/2021/08/using-1-2-ghz-in-the-colorado-14er-event/ https://www.k0nr.com/wordpress/2021/08/using-1-2-ghz-in-the-...
    - tombh 8mo ago
      244km! Oh wow, I never knew people did this kind of thing. Yeah this is exactly the sort of thing we want people to use the app for.
hybrid_study 8mo ago
Maybe including an actual picture of the sight would be helpful here?
- tombh 8mo ago
  This has been common feedback today. I hadn't appreciated the appetite for photos, but of course it makes sense. I think what we'll try to do is automate linking to some other tool that can produce a 3D panorama, like Google Earth for example.
justjash 8mo ago
Pretty interesting. I recently got some cheap Meshtastic devices just to play around with and it looks like the longest line of sight from my house is about 20 miles. Might have to leave one at home and see if I can directly connect to it from the general area it is showing.
- tombh 8mo ago
  Thanks, yes this is actually one of the legitimate usecases we hope for from our algorithm.
__mharrison__ 8mo ago
I was expecting photos...
- brucehoult 8mo ago
  Here's a not bad (and accidental!) 342 km one from 7 months ago: https://www.reddit.com/r/newzealand/comments/1m9p0bh/tapuaeoueneku_kaikoura_ranges_captured_from_the/ https://www.reddit.com/r/newzealand/comments/1m9p0bh/tapuaeo... In theory there should be a 365.3 km one just barely to the left of the obvious twin peaks, but I'm not seeing it. Quite a bit short of the longest in the world, but still pretty far to see.
crazygringo 8mo ago
This is so clever and interesting. Congratulations! But... I want to see a photo! Or at least what it looks like in Google Earth, with a red arrow marking the furthest point. It feels like the site is setting you up for the big suspense of the longest line of sight... and then it's just a line on a 2D map. I think it would also really help if the maps themselves were at an angle in 3D with an exaggerated relief, with the line drawn in 3D, so you can get a sense of how it travels between two peaks. It seems like you've put a ton of effort into this project. I think with just a tiny bit more work on the page, you could really put the "cherry on top". And with those visualizations, get it picked up by a lot of major news outlets. This is a really fun story, the kind of stuff newspapers and magazines love to run. It's easily understandable, it's a cool new "record", it's a story of someone's perseverance paying off, and then you show a Google Earth image simulating the view as the payoff. (And from slightly above, if necessary, to take account for refraction.) EDIT: Here, I used Google Earth to show the two points. Unfortunately it's from high above, since otherwise Earth wouldn't show the pin for Pik Dankova, but it at least gives a general idea of the area: https://imgur.com/hindu-kush-to-pik-dankova-530km-adbVFwb https://imgur.com/hindu-kush-to-pik-dankova-530km-adbVFwb And here is the Google Earth link for the view, but it doesn't contain the pins: https://earth.google.com/web/search/41.0181,77.6708/@36.66440293,78.68302029,3803.70648492a,64488.67604356d,35y,-10.37847318h,81.05180513t,360r/ https://earth.google.com/web/search/41.0181,77.6708/@36.6644...
- mrb 8mo ago
  For a 3D rendering of the longest sightline, see this direct panorama rendering: https://www.udeuschle.de/panoramas/panqueryfull.aspx?mode=newstandard&data=lon:77.684167$$$lat:41.059167$$$alt:auto$$$altcam:2$$$hialt:false$$$resolution:600$$$azimut:169.7$$$sweep:1$$$leftbound:169.2$$$rightbound:170.2$$$split:2$$$splitnr:1$$$tilt:-2.14166666666667$$$tiltsplit:false$$$elexagg:1$$$range:750$$$colorcoding:false$$$colorcodinglimit:493$$$title:Pik+Dankova$$$description:$$$email:$$$language:ge$$$screenwidth:2560$$$screenheight:1414 https://www.udeuschle.de/panoramas/panqueryfull.aspx?mode=ne... Note that technically my link is a slightly longer sightline (longer by 7 km).
  - lynnharry 8mo ago
werds 8mo ago
You can see Scotland from Wales! https://map.alltheviews.world/longest/-3.9754324057705617_53.16131292910862 https://map.alltheviews.world/longest/-3.9754324057705617_53...
- tombh 8mo ago
  Yes! It's the longest line of sight in the UK. I grew up in Wales so it was one of the first I looked for.
observationist 8mo ago
I found my big summer hike. It's the farthest point that can be seen from the highest point near where I live. I can make the hike and then get some pictures of that highest point, from the farthest point away it has a line of sight. Thanks for this tool!
- tombh 8mo ago
  Thank you! This is exactly the kind of thing I was hoping people would use this for.
comonoid 8mo ago
I've seen Mallorca from the Tibidabo mountain in Barcelona (the website states it is 194km). It required number of attempts for perfect atmosphere. This is an independent observation from the Fabra Observatory: https://english.elpais.com/elpais/2015/03/03/inenglish/1425385176_371052.html https://english.elpais.com/elpais/2015/03/03/inenglish/14253...
OhNoNotAgain_99 8mo ago
[dead]
croisillon 8mo ago
Related: https://news.ycombinator.com/item?id=34609865 https://news.ycombinator.com/item?id=34609865
keepamovin 8mo ago
And yet all you have to do is look up to the stars and you can see millions, trillions of kilometeres away. Starlight straight line of sight in so many directions. Almost nothing in the way. Crazy. This is cool tho. What about to an ocean point from a mountain? Was there anything longer?
lutusp 8mo ago
On this general topic, guess how distant the horizon (the "vanishing point") is, across open water, assuming clear weather and a six-foot-tall observer standing on a beach? The answer is a mere six miles. Next curious fact -- the two towers of the Golden Gate Bridge are perfectly vertical, but the top of one tower is 4.6 cm (1.8 inches) farther away from the other, compared to the bottom of the towers -- because there is a small angular tilt between the towers. Guess why ... Okay, it's because the towers are independently vertical with respect the center of the earth, are horizontally separated by 4,200 feet, and each tower is 746 feet tall. These dimensions assure that the towers have a distinct angle with respect to each other. It's a small difference, but it's not zero. I thought about these things (and many others) during my four-year solo around-the-world sail (https://arachnoid.com/sailbook/ https://arachnoid.com/sailbook/).
hdersch 8mo ago
"Viewsheds" of any location can be calculated and matched with photographs using "GeoImageViewer", an application I wrote a couple of years ago. Any feature in the photo can be interactively identified in a mapview and vice versa, including the boundary of the viewshed. See the link below for a couple of examples. I wonder how atmospheric refraction is handled in the calculations for the longest line of sight. Since it (a) strongly affects the line of sight, and (b) depends on temperature and weather, how is a static "world record" possible, or even defined? E.g. objects may appear 400m higher in 200km distance under typical conditions. https://hdersch.github.io/Viewing.html https://hdersch.github.io/Viewing.html
- tombh 8mo ago
  Oh hey, I remember you from the last time I posted something about our project. That's a great app you have. We actually have a plan to aggregate world runs together, so that one run as low refraction and a short observer, then another run with high refraction and tall observer. Then instead of rendering longest lines of sight as those singl triangles, we could render them as 2 triangles that represents the extremes of expected visibility.
_whiteCaps_ 8mo ago
Oh, neat. I do an amateur radio challenge called SOTA where any peak with 150m prominence is a candidate. British Columbia has detailed LIDAR data so I figure it would be straightforward to do, I just don't know anything about GIS to make it happen. I'll have to browse the repo for some hints.
sllabres 8mo ago
I think this is the furthest true photography [1] with 443 km distance, into the sunrise (corrected from sunset) [1] https://beyondrange.wordpress.com/2016/08/03/pic-de-finestrelles-pic-gaspard-ecrins-443-km/ https://beyondrange.wordpress.com/2016/08/03/pic-de-finestre...
- tombh 8mo ago
  The record was actually recently beaten https://www.guinnessworldrecords.com/world-records/66661-longest-line-of-sight-on-earth https://www.guinnessworldrecords.com/world-records/66661-lon...
  - sllabres 8mo ago
    Thanks, didn't knew that and 11% further is quite a increase and not too far from the maximum possible.
kawfey 8mo ago
The ham radio microwave community thanks you.
gfarah 8mo ago
Hi! Colombian here. I reviewed the second prediction and believe the tags are incorrect. They should be: Pico Lagos del Congo, Liborina, Antioquia to Pico Cristóbal Colón, Sierra Nevada, Magdalena. Additionally, the GPS coordinates might need adjustment, as there are several prominent peaks near both Liborina and Pico Cristóbal Colón (the summit of the Sierra Nevada mountains). [1] https://earth.google.com/web/search/6%2e75514,-75%2e7222/@6.7484571,-75.7321395,3327.45509177a,0d,35y,62.48243988h,95.50069314t,-0r/data=ClgaKhIkGRObj2tDBRtAIfVKWYY47lLAKhA2Ljc1NTE0LC03NS43MjIyGAEgASImCiQJPdG1m1OoIEARoX3WmQykFEAZGLE4kJYeUsAh1fn8e9q9U8BCAggBQgIIAEoNCP___________wEQAA https://earth.google.com/web/search/6%2e75514,-75%2e7222/@6.... [2] https://earth.google.com/web/search/10%2e8467,-73%2e7029/@10.84067595,-73.69972789,5254.08403793a,6218.60775951d,35y,174.43265444h,80.50818756t,360r/data=ClgaKhIkGeELk6mCsSVAIfAWSFD8bFLAKhAxMC44NDY3LC03My43MDI5GAEgASImCiQJKJG3UI9QG0AR0YoBqEPMGkAZV7kTHX_qUsAh8jrRNdfyUsBCAggBQgIIAEoNCP___________wEQAA https://earth.google.com/web/search/10%2e8467,-73%2e7029/@10...
- tombh 8mo ago
  Oye, fui a Colombia un par de veces! Y mi profesora Español era Colombiana. So you're saying a better title for the Colombian line of sight could be "Pico Lagos del Congo to Pico Cristóbal Colón"? We can definitely change that. Thought I'm not sure what you mean about the coordinates being wrong? Are you saying that you should be able to see further from Pico Lagos del Congo?
  - gfarah 8mo ago
    Yes! I think that might be a more exact title. This is what I mean: First point: - Mountain: Cerro Lago del Congo (The GPS coords refer to the peak) - Locality: Liborina - State: Antioquia Second point: - Mountain: Sierra Nevada de Santa Marta (The GPS coords refer to the peak, called Pico Cristóbal Colón) - Locality: Santa Marta - State: Magdalena Pd. Hope you enjoyed your visit! I think Colombia is beautiful (But hey! I am biased)
    - tombh 8mo ago
      Actualicé el website! Es mejor así?
LorenPechtel 8mo ago
Observations: 1) Poking around our local peaks I find that the calculation appears granular, it's offering me things I could see from the summit that I could not see from where I clicked. 2) It's offering me one I never even considered looking at (peeking just beside another mountain, the terrain appeared flat, I never realized there was a distant peak there) and one I knew about--and know I have no hope of actually seeing.
- tombh 8mo ago
  1) So you're expecting to click and see a line of sight that you've seen in real life? Is it just that each point only every records the _longest_, which not be the best or most notable view? 2) As in, in a good way?
  - LorenPechtel 8mo ago
    No. I'm saying that clicking near a peak was sometimes giving me views that would have required standing elsewhere. The mapping of whether I could see north or south (or neither--most of the trail on that ridgeline does not give views to the north or south) does not accurately correspond to the terrain in any fashion I can discern. And the second part was simply noting that just because there is a theoretical line of sight doesn't mean you can actually see. The southern view I know goes to haze long before what it's showing me, the northern view is such I didn't even realize there were mountains there beyond the big one close by.
    - tombh 8mo ago
      Oh, that sounds like an error on our part then. I'd really appreciate if you could paste the URL when one of those bad lines is rendered.
      - LorenPechtel 8mo ago
        I was looking around Mt. Charleston/Griffith Peak, southeastern Nevada. I've been on Griffith many times, Charleston twice. I was comparing what it showed me vs my experience. Your map actually shows the trail, most of that trail has little in the way of views to the other side of the respective peak--the peaks blot out a big chunk.
cvoss 8mo ago
What could be causing these large-scale grid lines to show up in the heatmap in Florida? https://map.alltheviews.world/longest/-83.1653564346176_29.874547620050393 https://map.alltheviews.world/longest/-83.1653564346176_29.8...
- tombh 8mo ago
  Oh wow, yes, very curious. I believe that is caused by the cleaning of the original NASA data by the creator of https://viewfinderpanoramas.org/dem3.html https://viewfinderpanoramas.org/dem3.html So whilst they improved the data, it still isn't perfect. Ultimately we plan to mix in higher resolution data from different more recent surveys.
fooker 8mo ago
Here's a potential bug report, but maybe it comes down to the resolution. There seems to be some missing data here when it comes to the north face of most Himalayan peaks (for example: Annapurna). I am willing to believe looking south gives you the longer view, but there has to be some points on the north faces that win out for a northern view. Fun fact, the view north is so far, clear and reliable weather-wise that the CIA partnered with mountaineers to set up equipment to monitor China's progress with nuclear weapons several decades ago.
- tombh 8mo ago
  Could you post a link to a view that you think might not be right?
  - fooker 8mo ago
    The 5-10 tiles north of the tall peaks. https://map.alltheviews.world/longest/88.14788327735505_27.707462778671186 https://map.alltheviews.world/longest/88.14788327735505_27.7... https://map.alltheviews.world/longest/88.14711648199943_27.704911881481124 https://map.alltheviews.world/longest/88.14711648199943_27.7...
    - tombh 8mo ago
      I see, thanks. So my thinking is that overly dark areas to the North are caused by _relatively_ low visibility. The heatmap is actually dynamically generated for every viewport. So I agree that there has to be some amazing view from those North faces, it's just that they are drowned out by the sheer enormity of the views on the South face. If were to use absolute global values for the heatmap, then the Himalayas would just appear as pure, washed-out white. Does that make sense?
12ian34 8mo ago
this is very cool, but i want to see photos!
stevage 8mo ago
I was in Kyrgyzstan last year and saw some distant mountains that I was able to work out were in Kazakhstan, over 100km away. Even that felt pretty amazing at the time. 500km? Whee...
cozzyd 8mo ago
I was wondering if this used a Gnomonic projection but the AEQD makes way more sense here (especially if defined in polar coordinates, as I imagine it must be? Then you only need to project the points you actually use?). Any chance of writing a QGIS plugin with the algorithm?
- tombh 8mo ago
  The AEQD projection radiates from the anchor right? Is that what you mean by polar coordinates? This was my first foray into optimising projections so if you have any insight I'd love to learn. If you know anything about QGIS plugins please feel free to make a brief write up in our issues https://github.com/AllTheLines/viewview/issues https://github.com/AllTheLines/viewview/issues
  - cozzyd 8mo ago
    I just mean that you only need it evaluated at the points along the azimuths you consider, but maybe that doesn't make sense computationally and it's faster to interpolate from a grid anyway. I might create an issue after I conceptualize what it might look like more!
fooker 8mo ago
What would it take to generate visualizations like this automagically? https://viewfinderpanoramas.org/panoramas/ASIA/EVEREST-SOUTH.gif https://viewfinderpanoramas.org/panoramas/ASIA/EVEREST-SOUTH...
- tombh 8mo ago
  I don't know, but I really want to do it.
enopod_ 8mo ago
Such a great project! I remember an older image of the french alps taken from the pyrenees, at over 400 km. Found it again here: https://beyondrange.wordpress.com/2016/08/03/pic-de-finestrelles-pic-gaspard-ecrins-443-km/ https://beyondrange.wordpress.com/2016/08/03/pic-de-finestre...
Quarrel 8mo ago
Great work and thanks for the write up. Sorry to be pedantic, your longest view is not from the Hindu Kush, but from the mountains to the south of the Tarim Basin which are the Kunlun mountains. The Hindu Kush are largely in Afghanistan, but also Pakistan, running in an arc from Kabul to the north east. They aren't in China. The Hindu Kush range then gives way to the Karakoram, as you cross Kashmir, which is then bordered to the north by the Kunlun which form the arc of the southern Tarim Basin. I suspect you're just mixing it up with the Hindu Tagh pass, just to the south of the peak your point is looking from. Hindu Tagh seems to be about as good a name as the line-of-sight community has come up with for that peak.
- ryanbberger 8mo ago
  We appreciate the pedantry. I think I came up with that name from a game of telephone of sources claiming to have the longest line of sight. There's a lot of really random sources on the Internet that mention the line of sight but do not cite the data or analysis. I have seen Hindu Tagh thrown around as well so if it's more accurate we want it there. Part of our motivations were to stop the game of telephone and become an authoritative source on this stuff. I'm not much of a geographer, more of a HPC guy. I have this on the TODO list to update tomorrow.
- tombh 8mo ago
  Agreed, pedantry very much appreciated. Website updated!
MomsAVoxell 8mo ago
This will be useful in the laser wars.
westurner 8mo ago
Isn't there a curved photonic beam method that technically, in space, can send a photon around the world at least once? Airy beams curve This type of amplification preserves the curvature of Airy beams FWIU: "Low-power integrated optical amplification through second-harmonic resonance" (2026) https://news.ycombinator.com/item?id=46824978 https://news.ycombinator.com/item?id=46824978 What kinds of sensing would be possible given a round-the-world photon trajectory? Quasiparticles have mass, and so might be easier to send around the world than purportedly massless photons. SQR Superfluid Quantum Relativity with a dilatant fluid says that the effects of mass energy equivalence at high velocities approaching c are actually due to the (atmospheric to superfluiic) viscosity of spacetime nonlinearly pushing back. But does that matter for a photon or a massless quasi-particle like a photon that we're trying to curve initially to send around the earth at least once to win teh line of sight distance ranking?
- westurner 8mo ago
  There is a theory that the star shafts of the Great Pyramid could have been used as waveguides. They did contain copper rods. Perhaps they were just lightning rods. If so, then the pyramids (and other ancient megalithic structures with quartz at 72 degree intervals) and Angkor Wat and Longyou caves and Osireon may have been the longest (non-) line of sight communication system back then in ancient times: https://gemini.google.com/share/101970a04402 https://gemini.google.com/share/101970a04402 Observation of a salt-formed Hydrogen-tuned NV-center diamond might resolve some of these claims?
username223 8mo ago
Thanks for confirming this! I read the speculation, and traveled fairly close to Dankova. Actually climbing it is a serious land expedition from the nearest international airport.
BobbyTables2 8mo ago
Would probably be really useful for Amateur Radio enthusiasts making low power long distance contacts using VHF/UHF. I wonder if air quality/humidity permit actually seeing this far though… That’s a lot more “air” than looking up toward space…
BuleBule 8mo ago
The jump from "we can compute this" to "we computed it for the entire planet" is what makes this impressive. A lot of projects stop at the proof of concept. Running hundreds of AMD Turin cores for two days straight to actually finish the job is a different kind of commitment. Curious about the edge cases, how do you handle atmospheric refraction at those distances? At 530km the curvature of the earth and atmospheric bending would meaningfully affect whether a line of sight is actually visible to a human observer versus just geometrically unobstructed.
- ryanbberger 8mo ago
  It was definitely quite a bit of effort to get every line of sight. We felt it was necessary if we were going to try and prove that there are none longer. Regular viewshed algorithms really aren't built for it, and being able to do it cheaply while also maintaining a cluster of compute that can shut down at any time is also its own mess (these were all spot instance so we could get 75+% off). The 530km number takes into account both the curvature, along with refraction. It's a simple elevation adjustment when you are doing your angle of elevation calculations. If you want a synopsis of how we calculate lines of sight and all the parameters we use I have a shorter, less whitepaper-y blog post here: https://ryan.berge.rs/posts/lines-of-sight/ https://ryan.berge.rs/posts/lines-of-sight/

412 points by tombh 8mo ago

umpriel 8mo ago

Claps!

ryanbberger 8mo ago
Thanks umpriel for the PR, hope you're well!

zoobab 8mo ago

Cool places to try wifi long shots. I did some longshots back in the early days of wifi.

ErroneousBosh 8mo ago
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.
- galangalalgol 8mo ago
  This data base could be used to optimally place meshtastic nodes.
- 1e1a 8mo ago
  You could just send raw 802.11 data frames and then receive them with monitor mode on the other end.
  - ErroneousBosh 8mo ago
    If I had just re-read Neal Stephenson's Cryptonomicon recently, which I have, I'd say that I'd set up a link using WEP-encrypted 802.11b and hammer data across it with odd little bits here and there designed to generate maximum spy interest. But then the actual message would be encoded by very slightly favouring the high or low end of the spread spectrum map as a kind of terribly slow FSK.
- zoobab 8mo ago
  For longshots, there was a value called "ack_timeout" that you needed to tune: https://gitlab.com/nsnam/ns-3-dev/-/issues/41 https://gitlab.com/nsnam/ns-3-dev/-/issues/41

jstanley 8mo ago

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/ https://incoherency.co.uk/line-of-sight-map/

eitally 8mo ago
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.
- arethuza 8mo ago
  I think the lines indicate areas that you can't see?
  - jychang 8mo ago
    It's buggy. Mission peak shows much of the bay area occluded.
- jstanley 8mo ago
  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 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!
- 1e1a 8mo ago
  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.

rob74 8mo ago

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?

tombh 8mo ago
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-longest-line-of-sight-on-earth 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.
- rob74 8mo ago
  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...

danielsamuels 8mo ago

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.

tombh 8mo ago
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.
DiggyJohnson 8mo ago
I think you're assuming more fidelity than the project is claiming
- danielsamuels 8mo ago
  I'm assuming that when the project says you can see 24 km from a given location, that you can see 24 km from that location. That's not the case. Fundamentally, it doesn't do what it claims to do. Why allow the user to select any arbitrary location on a map and give an answer when you know the answer is most likely nonsense? You don't need to compute for 2 days to accomplish that; you could just make it up.
  - crazygringo 8mo ago
    Surely you understand it's based on limited resolution data, and therefore intended to be used at the scale of general topography like mountains and valleys? That it's not taking into account human construction or distances of tens of meters? Presumably you can walk a little bit and climb on someone's roof to see the claimed 24.7 km. Assuming a sufficiently clear atmosphere, and that there isn't a tall office building in the way or something.
  - wat10000 8mo ago

brucehoult 8mo ago

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/tapuaeoueneku_kaikoura_ranges_captured_from_the/ 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).

repelsteeltje 8mo ago
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?
- kmaitreys 8mo ago
  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.
  - jmalicki 8mo ago
    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!

alvsilvao 8mo ago

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

ourmandave 8mo ago

Hopefully this won't become a tool for the Flat Earthers. =)

emiliobumachar 8mo ago
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.
tombh 8mo ago
We're actually thinking of writing a SIGBOVIK paper where we explore running this whole thing for a Flat Earth!

pestatije 8mo ago

It be nice to get the 3 or 5 longest distances from a specific point, not just the longestest

tombh 8mo ago
It's just a matter of storage costs. Even storing a single line of sight for every point on the planet is over 200GB!

noosphr 8mo ago

Since you have the data could you show how far you can see in every direction rather than the longest direction?

bartread 8mo ago
This would be incredible - please add this!
tombh 8mo ago
Yes, but, there's one small problem, storing this extra data for the whole world starts to run into the petabytes!
- em-bee 8mo ago
  what if you put a limit on it? like only a dozen views per point, and only views that are at least 100km. or only do this for peaks or points of interest. or some combination like more views for higher peaks, less for lower ones.
  - tombh 8mo ago
    Ohh yes, nice ideas.
    - em-bee 8mo ago
      i don't know if that makes sense but it could be interesting to split the views of any point into multiple segments, and then for each segment find the largest distance. next between two of these largest views find the shortest view. if the ends of each view are connected by lines the result would be a zigzag circle around the starting point that gives you a rough idea of the visible area. most points would be on a slope so they would just have a half circle, only peaks themselves would have an all around view.

drcongo 8mo ago

This is my favourite kind of HN post, and I absolutely love this one. Would love to see photos from each of these views.

tombh 8mo ago
Thank you <3 Well there is a photo near our #3 longest line of sight https://www.guinnessworldrecords.com/world-records/66661-longest-line-of-sight-on-earth https://www.guinnessworldrecords.com/world-records/66661-lon...
venusenvy47 8mo ago
I was looking for those on the website. Maybe we could find some photos on Google Maps that already exist from these locations.

em-bee 8mo ago

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?

laci37 8mo ago
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.
- tombh 8mo ago
  Exactly. And it could even be tweaked slightly with some favourable refraction.
  - stockresearcher 8mo ago
    Ah, well NASA left some mirrors on the surface of the moon so with some favorable reflection and infinite quality optics, you can theoretically see halfway around the world.

alansaber 8mo ago

This is the geography I was promised in school

1970-01-01 8mo ago

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.

tombh 8mo ago
Could it be this? https://www.udeuschle.de/panoramas/makepanoramas.htm https://www.udeuschle.de/panoramas/makepanoramas.htm
- 1970-01-01 8mo ago
  No, it used a much heavier JS interface and IIRC it also used Google Earth. That is a nice tool, thanks for sharing it.
sandos 8mo ago
heywhatsthat?
- 1970-01-01 8mo ago
  I think that was it, thank you for finding it again! Actually, I was thinking of https://caltopo.com/map.html https://caltopo.com/map.html but your site led me to it.
1970-01-01 8mo ago
It was https://caltopo.com/ https://caltopo.com/ https://www.heywhatsthat.com/ https://www.heywhatsthat.com/ is another bookmark that I had lost to time.

colechristensen 8mo ago

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.

tombh 8mo ago
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.
- colechristensen 8mo ago
  It's a sort of high-pass filter I guess? Using the curvature of the earth to highlight local changes in elevation.
  - tombh 8mo ago
    I'm not that familiar with high-pass filters. But yes it's the way it exposes local changes in elevation that is unique. Indeed the heatmap is generated dynamically for every change to the zoom and viewport.

sandos 8mo ago

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.

mrb 8mo ago

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 https://news.ycombinator.com/item?id=45512970) that's what Dr. Ulrich Deuschle also calculates (https://www.udeuschle.de/panoramas/panqueryfull.aspx?mode=newstandard&data=lon:77.684167$$$lat:41.059167$$$alt:auto$$$altcam:2$$$hialt:false$$$resolution:600$$$azimut:169.7$$$sweep:1$$$leftbound:169.2$$$rightbound:170.2$$$split:2$$$splitnr:1$$$tilt:-2.14166666666667$$$tiltsplit:false$$$elexagg:1$$$range:750$$$colorcoding:false$$$colorcodinglimit:493$$$title:Pik+Dankova$$$description:$$$email:$$$language:ge$$$screenwidth:2560$$$screenheight:1414 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%20viewfinderpanoramas_org3.htm 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 differing heights make no difference given the coarse DEM resolution). Something must be slighly off in your computations? Or do you think both Deuschle and I are wrong? Edit: to be clear the difference stems from our coordinates. Our starting points are: 41.059167,77.683333 (me) 41.0181,77.6708 (you) And our end points are: 36.295364,78.755593 (me) 36.314,78.7654 (you) Also I calculate the distance assuming the Earth is spherical (which gives 538 km) not the standard geodesic (which would give 537 km). And in the DEM data I measure the distance from the center of a cell to another (not the edge), while measuring from edge to edge may explain a difference of at most 0.1 km as the DEM resolution is 3 arcseconds. So clearly we disagree on the coordinates of the exact actual sightline as we have a 7 km difference :-) Edit #2: clearly the error is on your side. I should have checked this first, but the coordinates you give for the "To" point (41.0181,77.6708) land in a valley with the south view completely blocked so it's impossible to view 500+ km south as you claim. Look at where the marker lands on this Google Maps Terrain: https://maps.app.goo.gl/PgBWxi31WZC6vk3V9 https://maps.app.goo.gl/PgBWxi31WZC6vk3V9

ryanbberger 8mo ago
Hey Marc, Ryan here. Tom may respond as well There's two forms of interpolation going on here that I'm not sure you or Dr Dueschle are using. We interpolate a "band of sight" of single a degree for our azithmual projection, but uniquely we also rotate the DEM elevations around all the observers rather than the observer around to see all the elevations. The effects of the first can be lessened by lowering the band of sight such that we only process half a degree at a time so that we make sure we get more coverage further away. We plan on running some more experiments by rotating to cover more points. The algorithm is already fairly expensive to run against the whole world so we weren't particularly interested in that level of coverage for the full earth. For total viewshed area, our algorithm comes in at roughly a percent or so difference which was what we used as our benchmark for correctness. All this to say, no, we don't think you both are wrong, we've been looking at making ours more accurate. At a world scale that's quite computationally expensive, so we didn't use that methodology for our initial launch. We see our results as validation of yours, not as something we've disproved. Edit: grammar

IshKebab 8mo ago

Can you actually see anything in real life though?

tombh 8mo ago
The longest and second longest haven't been photographed yet, but #3 has https://www.guinnessworldrecords.com/world-records/66661-longest-line-of-sight-on-earth https://www.guinnessworldrecords.com/world-records/66661-lon...

amingilani 8mo ago

Now we just need to put two hams with 2m/70cm radios to make the longest line-of-sight QSO on the planet. Bonus points for QRP. Definitions: * Hams: Amateur radio operators. * QSO: conversation or contact between two radio stations. * QRP: Low power, typically under 5 watts.

tombh 8mo ago
That's actually one of the legitimate uses cases we've consider for the algorithm.
- stilldavid 8mo ago
  This is so rad! Here's a photo of me making a 1.2Ghz FM contact 244km away from the summit of a 14er to the summit of another 14er here in Colorado. That particular band is very line-of-sight, with not much propagation or reflections like even 2m SSB or the HF bands. This is a very fun tool that I can't wait to explore more! https://www.k0nr.com/wordpress/2021/08/using-1-2-ghz-in-the-colorado-14er-event/ https://www.k0nr.com/wordpress/2021/08/using-1-2-ghz-in-the-...
  - tombh 8mo ago
    244km! Oh wow, I never knew people did this kind of thing. Yeah this is exactly the sort of thing we want people to use the app for.

hybrid_study 8mo ago

Maybe including an actual picture of the sight would be helpful here?

tombh 8mo ago
This has been common feedback today. I hadn't appreciated the appetite for photos, but of course it makes sense. I think what we'll try to do is automate linking to some other tool that can produce a 3D panorama, like Google Earth for example.

justjash 8mo ago

Pretty interesting. I recently got some cheap Meshtastic devices just to play around with and it looks like the longest line of sight from my house is about 20 miles. Might have to leave one at home and see if I can directly connect to it from the general area it is showing.

tombh 8mo ago
Thanks, yes this is actually one of the legitimate usecases we hope for from our algorithm.

__mharrison__ 8mo ago

I was expecting photos...

brucehoult 8mo ago
Here's a not bad (and accidental!) 342 km one from 7 months ago: https://www.reddit.com/r/newzealand/comments/1m9p0bh/tapuaeoueneku_kaikoura_ranges_captured_from_the/ https://www.reddit.com/r/newzealand/comments/1m9p0bh/tapuaeo... In theory there should be a 365.3 km one just barely to the left of the obvious twin peaks, but I'm not seeing it. Quite a bit short of the longest in the world, but still pretty far to see.

crazygringo 8mo ago

This is so clever and interesting. Congratulations! But... I want to see a photo! Or at least what it looks like in Google Earth, with a red arrow marking the furthest point. It feels like the site is setting you up for the big suspense of the longest line of sight... and then it's just a line on a 2D map. I think it would also really help if the maps themselves were at an angle in 3D with an exaggerated relief, with the line drawn in 3D, so you can get a sense of how it travels between two peaks. It seems like you've put a ton of effort into this project. I think with just a tiny bit more work on the page, you could really put the "cherry on top". And with those visualizations, get it picked up by a lot of major news outlets. This is a really fun story, the kind of stuff newspapers and magazines love to run. It's easily understandable, it's a cool new "record", it's a story of someone's perseverance paying off, and then you show a Google Earth image simulating the view as the payoff. (And from slightly above, if necessary, to take account for refraction.) EDIT: Here, I used Google Earth to show the two points. Unfortunately it's from high above, since otherwise Earth wouldn't show the pin for Pik Dankova, but it at least gives a general idea of the area: https://imgur.com/hindu-kush-to-pik-dankova-530km-adbVFwb https://imgur.com/hindu-kush-to-pik-dankova-530km-adbVFwb And here is the Google Earth link for the view, but it doesn't contain the pins: https://earth.google.com/web/search/41.0181,77.6708/@36.66440293,78.68302029,3803.70648492a,64488.67604356d,35y,-10.37847318h,81.05180513t,360r/ https://earth.google.com/web/search/41.0181,77.6708/@36.6644...

mrb 8mo ago
For a 3D rendering of the longest sightline, see this direct panorama rendering: https://www.udeuschle.de/panoramas/panqueryfull.aspx?mode=newstandard&data=lon:77.684167$$$lat:41.059167$$$alt:auto$$$altcam:2$$$hialt:false$$$resolution:600$$$azimut:169.7$$$sweep:1$$$leftbound:169.2$$$rightbound:170.2$$$split:2$$$splitnr:1$$$tilt:-2.14166666666667$$$tiltsplit:false$$$elexagg:1$$$range:750$$$colorcoding:false$$$colorcodinglimit:493$$$title:Pik+Dankova$$$description:$$$email:$$$language:ge$$$screenwidth:2560$$$screenheight:1414 https://www.udeuschle.de/panoramas/panqueryfull.aspx?mode=ne... Note that technically my link is a slightly longer sightline (longer by 7 km).
- lynnharry 8mo ago

werds 8mo ago

You can see Scotland from Wales! https://map.alltheviews.world/longest/-3.9754324057705617_53.16131292910862 https://map.alltheviews.world/longest/-3.9754324057705617_53...

tombh 8mo ago
Yes! It's the longest line of sight in the UK. I grew up in Wales so it was one of the first I looked for.

observationist 8mo ago

I found my big summer hike. It's the farthest point that can be seen from the highest point near where I live. I can make the hike and then get some pictures of that highest point, from the farthest point away it has a line of sight. Thanks for this tool!

tombh 8mo ago
Thank you! This is exactly the kind of thing I was hoping people would use this for.

comonoid 8mo ago

I've seen Mallorca from the Tibidabo mountain in Barcelona (the website states it is 194km). It required number of attempts for perfect atmosphere. This is an independent observation from the Fabra Observatory: https://english.elpais.com/elpais/2015/03/03/inenglish/1425385176_371052.html https://english.elpais.com/elpais/2015/03/03/inenglish/14253...

OhNoNotAgain_99 8mo ago

[dead]

croisillon 8mo ago

Related: https://news.ycombinator.com/item?id=34609865 https://news.ycombinator.com/item?id=34609865

keepamovin 8mo ago

And yet all you have to do is look up to the stars and you can see millions, trillions of kilometeres away. Starlight straight line of sight in so many directions. Almost nothing in the way. Crazy. This is cool tho. What about to an ocean point from a mountain? Was there anything longer?

lutusp 8mo ago

On this general topic, guess how distant the horizon (the "vanishing point") is, across open water, assuming clear weather and a six-foot-tall observer standing on a beach? The answer is a mere six miles. Next curious fact -- the two towers of the Golden Gate Bridge are perfectly vertical, but the top of one tower is 4.6 cm (1.8 inches) farther away from the other, compared to the bottom of the towers -- because there is a small angular tilt between the towers. Guess why ... Okay, it's because the towers are independently vertical with respect the center of the earth, are horizontally separated by 4,200 feet, and each tower is 746 feet tall. These dimensions assure that the towers have a distinct angle with respect to each other. It's a small difference, but it's not zero. I thought about these things (and many others) during my four-year solo around-the-world sail (https://arachnoid.com/sailbook/ https://arachnoid.com/sailbook/).

hdersch 8mo ago

"Viewsheds" of any location can be calculated and matched with photographs using "GeoImageViewer", an application I wrote a couple of years ago. Any feature in the photo can be interactively identified in a mapview and vice versa, including the boundary of the viewshed. See the link below for a couple of examples. I wonder how atmospheric refraction is handled in the calculations for the longest line of sight. Since it (a) strongly affects the line of sight, and (b) depends on temperature and weather, how is a static "world record" possible, or even defined? E.g. objects may appear 400m higher in 200km distance under typical conditions. https://hdersch.github.io/Viewing.html https://hdersch.github.io/Viewing.html

tombh 8mo ago
Oh hey, I remember you from the last time I posted something about our project. That's a great app you have. We actually have a plan to aggregate world runs together, so that one run as low refraction and a short observer, then another run with high refraction and tall observer. Then instead of rendering longest lines of sight as those singl triangles, we could render them as 2 triangles that represents the extremes of expected visibility.

_whiteCaps_ 8mo ago

Oh, neat. I do an amateur radio challenge called SOTA where any peak with 150m prominence is a candidate. British Columbia has detailed LIDAR data so I figure it would be straightforward to do, I just don't know anything about GIS to make it happen. I'll have to browse the repo for some hints.

sllabres 8mo ago

I think this is the furthest true photography [1] with 443 km distance, into the sunrise (corrected from sunset) [1] https://beyondrange.wordpress.com/2016/08/03/pic-de-finestrelles-pic-gaspard-ecrins-443-km/ https://beyondrange.wordpress.com/2016/08/03/pic-de-finestre...

tombh 8mo ago
The record was actually recently beaten https://www.guinnessworldrecords.com/world-records/66661-longest-line-of-sight-on-earth https://www.guinnessworldrecords.com/world-records/66661-lon...
- sllabres 8mo ago
  Thanks, didn't knew that and 11% further is quite a increase and not too far from the maximum possible.

kawfey 8mo ago

The ham radio microwave community thanks you.

gfarah 8mo ago

Hi! Colombian here. I reviewed the second prediction and believe the tags are incorrect. They should be: Pico Lagos del Congo, Liborina, Antioquia to Pico Cristóbal Colón, Sierra Nevada, Magdalena. Additionally, the GPS coordinates might need adjustment, as there are several prominent peaks near both Liborina and Pico Cristóbal Colón (the summit of the Sierra Nevada mountains). [1] https://earth.google.com/web/search/6%2e75514,-75%2e7222/@6.7484571,-75.7321395,3327.45509177a,0d,35y,62.48243988h,95.50069314t,-0r/data=ClgaKhIkGRObj2tDBRtAIfVKWYY47lLAKhA2Ljc1NTE0LC03NS43MjIyGAEgASImCiQJPdG1m1OoIEARoX3WmQykFEAZGLE4kJYeUsAh1fn8e9q9U8BCAggBQgIIAEoNCP___________wEQAA https://earth.google.com/web/search/6%2e75514,-75%2e7222/@6.... [2] https://earth.google.com/web/search/10%2e8467,-73%2e7029/@10.84067595,-73.69972789,5254.08403793a,6218.60775951d,35y,174.43265444h,80.50818756t,360r/data=ClgaKhIkGeELk6mCsSVAIfAWSFD8bFLAKhAxMC44NDY3LC03My43MDI5GAEgASImCiQJKJG3UI9QG0AR0YoBqEPMGkAZV7kTHX_qUsAh8jrRNdfyUsBCAggBQgIIAEoNCP___________wEQAA https://earth.google.com/web/search/10%2e8467,-73%2e7029/@10...

tombh 8mo ago
Oye, fui a Colombia un par de veces! Y mi profesora Español era Colombiana. So you're saying a better title for the Colombian line of sight could be "Pico Lagos del Congo to Pico Cristóbal Colón"? We can definitely change that. Thought I'm not sure what you mean about the coordinates being wrong? Are you saying that you should be able to see further from Pico Lagos del Congo?
- gfarah 8mo ago
  Yes! I think that might be a more exact title. This is what I mean: First point: - Mountain: Cerro Lago del Congo (The GPS coords refer to the peak) - Locality: Liborina - State: Antioquia Second point: - Mountain: Sierra Nevada de Santa Marta (The GPS coords refer to the peak, called Pico Cristóbal Colón) - Locality: Santa Marta - State: Magdalena Pd. Hope you enjoyed your visit! I think Colombia is beautiful (But hey! I am biased)
  - tombh 8mo ago
    Actualicé el website! Es mejor así?

LorenPechtel 8mo ago

Observations: 1) Poking around our local peaks I find that the calculation appears granular, it's offering me things I could see from the summit that I could not see from where I clicked. 2) It's offering me one I never even considered looking at (peeking just beside another mountain, the terrain appeared flat, I never realized there was a distant peak there) and one I knew about--and know I have no hope of actually seeing.

tombh 8mo ago
1) So you're expecting to click and see a line of sight that you've seen in real life? Is it just that each point only every records the _longest_, which not be the best or most notable view? 2) As in, in a good way?
- LorenPechtel 8mo ago
  No. I'm saying that clicking near a peak was sometimes giving me views that would have required standing elsewhere. The mapping of whether I could see north or south (or neither--most of the trail on that ridgeline does not give views to the north or south) does not accurately correspond to the terrain in any fashion I can discern. And the second part was simply noting that just because there is a theoretical line of sight doesn't mean you can actually see. The southern view I know goes to haze long before what it's showing me, the northern view is such I didn't even realize there were mountains there beyond the big one close by.
  - tombh 8mo ago
    Oh, that sounds like an error on our part then. I'd really appreciate if you could paste the URL when one of those bad lines is rendered.
    - LorenPechtel 8mo ago
      I was looking around Mt. Charleston/Griffith Peak, southeastern Nevada. I've been on Griffith many times, Charleston twice. I was comparing what it showed me vs my experience. Your map actually shows the trail, most of that trail has little in the way of views to the other side of the respective peak--the peaks blot out a big chunk.

cvoss 8mo ago

What could be causing these large-scale grid lines to show up in the heatmap in Florida? https://map.alltheviews.world/longest/-83.1653564346176_29.874547620050393 https://map.alltheviews.world/longest/-83.1653564346176_29.8...

tombh 8mo ago
Oh wow, yes, very curious. I believe that is caused by the cleaning of the original NASA data by the creator of https://viewfinderpanoramas.org/dem3.html https://viewfinderpanoramas.org/dem3.html So whilst they improved the data, it still isn't perfect. Ultimately we plan to mix in higher resolution data from different more recent surveys.

fooker 8mo ago

Here's a potential bug report, but maybe it comes down to the resolution. There seems to be some missing data here when it comes to the north face of most Himalayan peaks (for example: Annapurna). I am willing to believe looking south gives you the longer view, but there has to be some points on the north faces that win out for a northern view. Fun fact, the view north is so far, clear and reliable weather-wise that the CIA partnered with mountaineers to set up equipment to monitor China's progress with nuclear weapons several decades ago.

tombh 8mo ago
Could you post a link to a view that you think might not be right?
- fooker 8mo ago
  The 5-10 tiles north of the tall peaks. https://map.alltheviews.world/longest/88.14788327735505_27.707462778671186 https://map.alltheviews.world/longest/88.14788327735505_27.7... https://map.alltheviews.world/longest/88.14711648199943_27.704911881481124 https://map.alltheviews.world/longest/88.14711648199943_27.7...
  - tombh 8mo ago
    I see, thanks. So my thinking is that overly dark areas to the North are caused by _relatively_ low visibility. The heatmap is actually dynamically generated for every viewport. So I agree that there has to be some amazing view from those North faces, it's just that they are drowned out by the sheer enormity of the views on the South face. If were to use absolute global values for the heatmap, then the Himalayas would just appear as pure, washed-out white. Does that make sense?

12ian34 8mo ago

this is very cool, but i want to see photos!

stevage 8mo ago

I was in Kyrgyzstan last year and saw some distant mountains that I was able to work out were in Kazakhstan, over 100km away. Even that felt pretty amazing at the time. 500km? Whee...

cozzyd 8mo ago

I was wondering if this used a Gnomonic projection but the AEQD makes way more sense here (especially if defined in polar coordinates, as I imagine it must be? Then you only need to project the points you actually use?). Any chance of writing a QGIS plugin with the algorithm?

tombh 8mo ago
The AEQD projection radiates from the anchor right? Is that what you mean by polar coordinates? This was my first foray into optimising projections so if you have any insight I'd love to learn. If you know anything about QGIS plugins please feel free to make a brief write up in our issues https://github.com/AllTheLines/viewview/issues https://github.com/AllTheLines/viewview/issues
- cozzyd 8mo ago
  I just mean that you only need it evaluated at the points along the azimuths you consider, but maybe that doesn't make sense computationally and it's faster to interpolate from a grid anyway. I might create an issue after I conceptualize what it might look like more!

fooker 8mo ago

What would it take to generate visualizations like this automagically? https://viewfinderpanoramas.org/panoramas/ASIA/EVEREST-SOUTH.gif https://viewfinderpanoramas.org/panoramas/ASIA/EVEREST-SOUTH...

tombh 8mo ago
I don't know, but I really want to do it.

enopod_ 8mo ago

Such a great project! I remember an older image of the french alps taken from the pyrenees, at over 400 km. Found it again here: https://beyondrange.wordpress.com/2016/08/03/pic-de-finestrelles-pic-gaspard-ecrins-443-km/ https://beyondrange.wordpress.com/2016/08/03/pic-de-finestre...

Quarrel 8mo ago

Great work and thanks for the write up. Sorry to be pedantic, your longest view is not from the Hindu Kush, but from the mountains to the south of the Tarim Basin which are the Kunlun mountains. The Hindu Kush are largely in Afghanistan, but also Pakistan, running in an arc from Kabul to the north east. They aren't in China. The Hindu Kush range then gives way to the Karakoram, as you cross Kashmir, which is then bordered to the north by the Kunlun which form the arc of the southern Tarim Basin. I suspect you're just mixing it up with the Hindu Tagh pass, just to the south of the peak your point is looking from. Hindu Tagh seems to be about as good a name as the line-of-sight community has come up with for that peak.

ryanbberger 8mo ago
We appreciate the pedantry. I think I came up with that name from a game of telephone of sources claiming to have the longest line of sight. There's a lot of really random sources on the Internet that mention the line of sight but do not cite the data or analysis. I have seen Hindu Tagh thrown around as well so if it's more accurate we want it there. Part of our motivations were to stop the game of telephone and become an authoritative source on this stuff. I'm not much of a geographer, more of a HPC guy. I have this on the TODO list to update tomorrow.
tombh 8mo ago
Agreed, pedantry very much appreciated. Website updated!

MomsAVoxell 8mo ago

This will be useful in the laser wars.

westurner 8mo ago

Isn't there a curved photonic beam method that technically, in space, can send a photon around the world at least once? Airy beams curve This type of amplification preserves the curvature of Airy beams FWIU: "Low-power integrated optical amplification through second-harmonic resonance" (2026) https://news.ycombinator.com/item?id=46824978 https://news.ycombinator.com/item?id=46824978 What kinds of sensing would be possible given a round-the-world photon trajectory? Quasiparticles have mass, and so might be easier to send around the world than purportedly massless photons. SQR Superfluid Quantum Relativity with a dilatant fluid says that the effects of mass energy equivalence at high velocities approaching c are actually due to the (atmospheric to superfluiic) viscosity of spacetime nonlinearly pushing back. But does that matter for a photon or a massless quasi-particle like a photon that we're trying to curve initially to send around the earth at least once to win teh line of sight distance ranking?

westurner 8mo ago
There is a theory that the star shafts of the Great Pyramid could have been used as waveguides. They did contain copper rods. Perhaps they were just lightning rods. If so, then the pyramids (and other ancient megalithic structures with quartz at 72 degree intervals) and Angkor Wat and Longyou caves and Osireon may have been the longest (non-) line of sight communication system back then in ancient times: https://gemini.google.com/share/101970a04402 https://gemini.google.com/share/101970a04402 Observation of a salt-formed Hydrogen-tuned NV-center diamond might resolve some of these claims?

username223 8mo ago

Thanks for confirming this! I read the speculation, and traveled fairly close to Dankova. Actually climbing it is a serious land expedition from the nearest international airport.

BobbyTables2 8mo ago

Would probably be really useful for Amateur Radio enthusiasts making low power long distance contacts using VHF/UHF. I wonder if air quality/humidity permit actually seeing this far though… That’s a lot more “air” than looking up toward space…

BuleBule 8mo ago

The jump from "we can compute this" to "we computed it for the entire planet" is what makes this impressive. A lot of projects stop at the proof of concept. Running hundreds of AMD Turin cores for two days straight to actually finish the job is a different kind of commitment. Curious about the edge cases, how do you handle atmospheric refraction at those distances? At 530km the curvature of the earth and atmospheric bending would meaningfully affect whether a line of sight is actually visible to a human observer versus just geometrically unobstructed.

ryanbberger 8mo ago
It was definitely quite a bit of effort to get every line of sight. We felt it was necessary if we were going to try and prove that there are none longer. Regular viewshed algorithms really aren't built for it, and being able to do it cheaply while also maintaining a cluster of compute that can shut down at any time is also its own mess (these were all spot instance so we could get 75+% off). The 530km number takes into account both the curvature, along with refraction. It's a simple elevation adjustment when you are doing your angle of elevation calculations. If you want a synopsis of how we calculate lines of sight and all the parameters we use I have a shorter, less whitepaper-y blog post here: https://ryan.berge.rs/posts/lines-of-sight/ https://ryan.berge.rs/posts/lines-of-sight/