Show HN: What country you would hit if you went straight where you're pointing

[brgross]

This app was designed to answer my wife’s question “what country would we hit if we went straight” (generally posed while pointing her phone)

But with two additional twists:

1. It loads up historical maps from different years (right now 1 BC, 700 AD, 1000 AD, 1300 AD, 1800 AD, 1900 AD) so you can see what you would hit if you had a time machine AND you went in the direction your phone is pointing

2. Tap a country/territory for an (AI-generated) blurb on what you are pointing at

How it works: Starting from your phone’s bearing, we trace the great-circle in 200 km steps, prefilter candidate countries with bounding boxes (~5–10 instead of ~200), then check ~20 km points along each segment to catch coastlines and stop when the path first enters another country.

Great-circles (https://www.movable-type.co.uk/scripts/latlong.html) are why you can hit Australia from NYC, even though when you look at a flat map that can be hard to see.

There might be some weird stuff in the explanations, I haven’t read all 1,400 of them. If you see something weird let me know and I will update it!

The app is free and doesn’t have ads or tracking — your location and bearing are only used locally to figure out where you are and what you’re pointing at

Probably will work best if you hold your phone pretty flat :)

Thank you to André Ourednik and all the contributors to the Historical Basemaps project: https://github.com/aourednik/historical-basemaps)

[mrgriscom]

This question ate away at me too, and I also scratched the itch: https://mrgris.com/projects/landfall/

Specifically mine deals with what you'd hit looking across the ocean from a coast. I had long wanted to make mine an interactive app but could never fully motivate myself to do it, so congrats for shipping.

[lastofthemojito]

Very neat! I was confused as to how the possible paths would lead me to France, or if I slightly moved my phone, Brazil. Then I remembered French Guiana - it might be worth adding awareness of things like overseas departments rather than just the parent country.

Also, it reminds me of this HN conversation I found fascinating a few years back: Finding the longest straight line you could sail without hitting land - https://news.ycombinator.com/item?id=16965650

[thebruce87m]

My aunt and uncle were disembarked from a cruise ship because they were ill (covid) and they were taken to hospital. They phoned my mum to tell her of the situation while still disoriented and said they were in Spain.

The Canary Islands are Spanish, but saying Spain in this situation wasn’t helpful when my mum was trying to book flights. Caused some mild confusion for a while.

[devilbunny]

So I just spent a few minutes playing with Great Circle Mapper and while it's not exactly definitive (you get a static image, no zooming) it appears that leaving from Greater London and heading in a great-circle direction toward the northeast coast of Brazil, there are indeed some combination of your location and precisely where you point the phone that you either pick up Finisterre, metropolitan France, or Brazil. I suppose if you kept going you would pick up France again as in the territory of French Guiana.

Going from, say, Land's End, it looked a bit more likely to nick northern Galicia.

[netsharc]

> it might be worth adding awareness of things like overseas departments rather than just the parent country.

I'd guess showing the coordinates of the hit (and make it a link to maps) would be beneficial.

[FredPret]

France is the country with the most surprising shape. Most of it is in Europe but the rest covers many timezones and several continents.

[dilap]

This is cool! Immediately upon playing with it I find I want more features :-)

- Ability to toggle ocean traversal off/on

- Ability to see route on a map

- AI generated summary of the trip if I took it -- what things did I see along the way? (Should reference real map data, then make up a story; matching local culture etc.)

[brgross]

Love these ideas -- I've also been thinking about an "arcade" mode where you get prompted with a country "in sight" and you have to guess the bearing

[adamcharnock]

Very cool and fun!

The first thing did when I opened it was to point my phone at the floor though, trying to find Australia. Took me a moment to realise it wasn’t that kind of pointer!

[jvanderbot]

I was on vacation in Baja Mexico. South of California. We were having dinner on the beach and my wife asked "I wonder how far you can go before you hit land".

Later some basic Geo calculations and a Google maps visit to estimate the bearing she was looking and yeah, the great circle arc went all the way to Antarctica, crossing half a planet.

Its remarkable how huge the Pacific Ocean is. Its Vast.

[afandian]

This seems to be from the same universe as the excellent https://pointerpointer.com/

[mk89]

Not sure what this has to do with the app.

I cannot install the app right now, but it seems to be really educational/entertaining more than just "fun", if that's fun...

[amelius]

Maybe you can do this with other things too. For example cities, buildings (clubs, shops, etc) or even people.

[munchler]

I think about this sometimes, so I like the idea, but how do you define “straight” on an oblate spheroid? Great circle, constant direction (e.g. “due east”), or something else?

[lqr]

The mathematical field of Differential Geometry can answer this question precisely: https://en.wikipedia.org/wiki/Geodesic#Affine_geodesics

An oblate spheroid is an example of a Riemannian manifold: a smooth object that looks like a plane (or, in general, any ℝ^n) locally, and has a way to measure angles between vectors in that local plane.

All Riemannian manifolds have an object called the Levi-Cevita connection, which defines how vectors in the local plane (tangent space) most naturally map to vectors in other tangent spaces in the immediate neighborhood.

Standing at a point on the Earth and looking in a certain direction gives us 1) a point on the manifold, and 2) a direction in that point's tangent space.

We then take an infinitesimally small step forward, and apply the Levi-Cevita connection to get from the old tangent space to the (infinitesimally nearby) new tangent space, and repeat. This defines an ordinary differential equation. Integrating the differential equation gives us a curve through the manifold.

Within some neighborhood of the initial point, this curve is a geodesic, i.e. the shortest path between the initial point and all subsequent points on the curve. This matches our typical intuition of "straight".

(Disclaimer: I am currently learning about this topic, but am not an expert.)

edit: https://en.wikipedia.org/wiki/Geodesics_on_an_ellipsoid goes into some interesting specifics about the results of this process on ellipsoids.

[brgross]

I went with great circles since that feels like the most “natural” straight line on a sphere — the path you’d walk if you just kept going forward without steering. You could define "straight" as a constant compass direction (I think it's called a "rhumb") -- that would look straight on a Mercator map but would actually require regular steering adjustments to maintain the bearing.

[diggan]

Probably not scientifically accurate or anything, but if you point somewhere, then "straight" is in that direction. I guess it'll loose accuracy as you get further and further in the distance of the direction, but probably for most people would be good enough for "straight in that direction" :)

[andrewstuart]

Installed it, love it.

It’s a 30 second novelty I’ll show to friends.

It would be great if the line continued rather than stopping g at the first country.

For example which direction is Japan? I think it might be behind Papua New Guinea.

[umanwizard]

Cool!

One of the countries in 1800 renders as “M?ori” for me, so it looks like you have some kind of character encoding issues (or there’s some language I don’t know about where ? is a letter).

Feature request: is there a way to get a blurb about one’s current country? Lots of people on this site will get “Viceroyalty of New Spain” (the pre-independence name of Mexico, which included the entire current American Southwest incl. California and Texas) when they switch to 1800 and might want to learn more about it.

[robinhouston]

I think this error may be in the historical-basemaps data, because it is also present on https://historicborders.app/year/1800?lng=169.5234304&lat=-4...

[wink]

This actually took a while to grasp the concept of. Where I'm living (so far from the coast that it might as well be landlocked) it took a while of eyeballing on a map, but I did find one angle where it's not kinda common sense where I would land. I suppose this is a lot more fun if you live near the coast and the answer is not completely obvious to anyone who knows the neighboring countries.

[FredPret]

I love that you can set the date. Apparently I'm looking at where the "plateau fishers and hunter-gatherers" were at 1 BC.

[cozzyd]

I suppose the heading error from the compass is so large there is little reason to use the real geodesic (https://link.springer.com/article/10.1007/s00190-012-0578-z) as opposed to the great circle

[busfahrer]

Neat! I think I found a bug though? I'm in Southern Germany, and for some direction south of me it showed me Italy, which doesn't border Germany, I think

edit: As a wild guess, it might have something to do with scanning resolution? Austria's western "arm" is only about 40 kms across

[dmd]

I'm very confused. I'm in Boston, and if I face 270, I get Canada, but if I face 269.9, I get Mexico.

I feel like there should be something across the Pacific between Canada and Mexico.

[flowardnut]

I wrote one of these but it only works for residents of san marino

[EdSchouten]

Soon available for people in the Vatican as well?

[sdotdev]

AI icon might throw people off but its a good concept i like it

[m-hodges]

This is incredible timing as I was having my own version of this question with family last week!

[jjtheblunt]

your app company name of Gross National Products made me smile. well done!

[abdullahkhalids]

Does this take into account the fact that the Earth is not a perfect sphere?

[lawrencegripper]

Very cool, me and my kids been playing and enjoying it. Nice work!