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

apps.apple.com

32 points by brgross 4 hours ago

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)

dilap - 34 minutes ago

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 - 3 minutes ago

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

mrgriscom - an hour ago

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.

afandian - 29 minutes ago

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

munchler - 2 hours ago

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 - 17 minutes ago

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 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) 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.)
brgross - an hour ago

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.
- munchler - an hour ago
  
  That makes sense, but I think constant latitude, in particular, is a special case that people often have in mind.
  - zamadatix - 25 minutes ago
    
    The other methods are about defining different meanings of what "going around" actually is while constant latitude is a special case of many such methods, e.g. great circle, not a new definition of what going that way means.
  - - 28 minutes ago
    
    [deleted]
diggan - 2 hours ago

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" :)
- munchler - an hour ago
  
  An actual straight line would be tangent to the earth at that point, so I don’t think that would work well for anything over a few hundred miles.
  - floatrock - an hour ago
    
    App should be "What star you would hit if you went straight where you're pointing"

FredPret - an hour ago

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

umanwizard - 2 hours ago

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 - an hour ago

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...

andrewstuart - 9 minutes ago

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.

abdullahkhalids - an hour ago

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