hckrnws

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

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.

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.

> 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.

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

Saint Pierre et Miquelon is a perfect example with it being a french territory inside canada.

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.

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!

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.)

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

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

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

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...

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?

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.

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.

That makes sense, but I think constant latitude, in particular, is a special case that people often have in mind.

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.

I'm not sure what you mean, but a circle of constant latitude is definitely not a great circle (except on the equator).

You're 100% right, I conflated great circle and small circle there.

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" :)

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.

App should be "What star you would hit if you went straight where you're pointing"

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.

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...

It's more than character encoding. If you click on it, the description of New Zealand is "a quintuple star system some 1,200 light-years from the Sun"

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

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

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

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

Soon available for people in the Vatican as well?

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

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

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.