Solver geolocates a resort island using triangle geometry and CUDA
A writeup for OSINT puzzle Gralhix 004 fingerprints a drone photo's island triangle and brute-forces it against global coastline data on GPU.
What to know
- A writeup for the 'Gralhix 004' OSINT puzzle geolocates a resort island by building a triangle geometry fingerprint from three visible islands in a drone photo.
- The author deliberately avoided reverse-image tools like Google Lens, instead brute-forcing the triangle against global OpenStreetMap coastline data using one CUDA thread per candidate triangle.
- The post reached the Hacker News frontpage (score 226, 46 comments) and was mirrored to Lobsters and Mastodon, where one poster mocked the approach and questioned whether it was genuinely human-made work.
yassa9 Author of the geolocation writeupSofia Santos | Gralhix Creator of the Gralhix OSINT challenge seriesngate@mastodon.social Mastodon commenter
How it unfolded 4 developments, newest first · click a bar or a number to jump articlesposts
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Additional Mastodon relay reposts the story
A Mastodon relay bot re-shares the Hacker News link and discussion thread, continuing cross-platform circulation of the writeup.
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People liking this post will probably like this [1] and especially these [2] from the channel. All solved using algorithms and map data.[1]
2 more of the top 3 · 5 posts in this stretch
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> NOTE: this is a genuine human work, didnt use LLM generation.I'm sorry, but I don't believe this. The article reads like LLM text post-edited by an AI prompted to "write like a non-native English speaker, replace you for u, make errors, etc".The other pages on your site are cough, "the smoking gun". For instance, your "Suckless, single binary…
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Super fun! Interestingly, this is how JPL was able to significantly reduce the Mars 2020 landing radius on Mars. Cameras onboard take pictures of the terrain and match that to maps to figure out where the lander is.
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Lobsters community mirrors the writeup
The same writeup is cross-posted to Lobsters under the title 'Geolocating Random Islet Image Using Geometry & CUDA GPU Programming', gaining a modest score with no comments yet.
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first by HN Best, 62d ago · also HN Frontpage
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Excellent write up and an enjoyable read! Reminds me of the “good old times” where posts on HN were written by humans and with a specific writing style like yours. You could’ve used a little bit more of geoguessing to narrow down results, or do a brute force visual check on the last hundred or so ;-)
2 more of the top 3 · 5 posts in this stretch
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This is awesome. I worked on something similar a few months ago. It is a general purpose navigation system based on TERCOM and dead reckoning -
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yea, thanks :D , I used a tiny idea from geoguessing, that I banded the search on islands only in latitude between -30 to +30 deg. based on the sky and the tropical vibes in the img , and it worked !
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Mastodon poster mocks the method and questions authorship
A Mastodon account reacts sarcastically to the approach, framing it as overkill compared to Google Lens and casting doubt on whether the writeup is genuinely human-authored work.
“🤦♂️ So someone decided to play "Where's Waldo?" with an island using geometry and GPU programming. Because clearly, using Google Lens is just too mainstream for the cool kids with their ✨CUDA skills✨. And remember, this is absolutely, positively, 100% human work!”
— ngate@mastodon.social -
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🤦♂️ So someone decided to play "Where's Waldo?" with an island using # geometry and GPU programming. Because clearly, using Google Lens is just too mainstream for the cool kids with their ✨CUDA skills✨. And remember, this is absolutely, positively, 100% human work! (As if anyone else would claim it 🤷♀️). https:// yassa9.github.io/osint/gralhix…
2 more of the top 3 · 3 posts in this stretch
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For drones and missiles, this technique is known as Terrain Contour Matching. If terrain contour are measured optically, navigation is independent of RF jamming, unlike GNSS.
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OpenStreetMap data really is a godsend for such OSINT purposes. Works much better in populated areas too, with more features like roads, shops, electric lines that can be used to search.
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Hacker News frontpage picks up the writeup
The post climbs to a score of 226 with 46 comments on Hacker News after being submitted, and is separately flagged by the HN Frontpage RSS feed.
“In my opinion, solving this challenge with google lens is wasting a fun opportunity, so decided to solve it with math and programming.”
— yassa9, Author of the writeup · source -
background
yassa9 publishes CUDA/geometry solution to island geolocation puzzle — The writeup solves Gralhix challenge 004 by clicking pixel coordinates of three islands to build a triangle geometry fingerprint, then filtering global OpenStreetMap land-polygon data (882MB) by tropical latitude, point density and cluster size before running a CUDA kernel that gives one GPU thread per candidate triangle to find a real-world match.
What people are saying 4 voices from 1 site · best of 13 · verbatim
- Aug 19
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A help with this is the sun is to the left and it seems to be midday, so you could answer the "cardinal direction" question just from the picture with "west ish", which is what it turns out to be.
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I find it highly ironic that his is the second article on the main page right after "avoid building technologies that could be used by a police state".
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Really great article! OP, you did an awesome job breaking down a complex problem into manageable chunks and synthesizing the solution.
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What do you mean by no LLM generation if an LLM did all the coding based on reading through the .py files? Pangram isn't kind to "your" text either.