Show HN: What country you would hit if you went straight where you're pointing
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)
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!
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
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.
I'd guess showing the coordinates of the hit (and make it a link to maps) would be beneficial.
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.
- 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.)
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.
I cannot install the app right now, but it seems to be really educational/entertaining more than just "fun", if that's fun...
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.
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.