Dead Reckoning
damninteresting.com188 points by repost_bot 5 days ago
188 points by repost_bot 5 days ago
My favorite application of dead reckoning is the early 80's Honda system to display the car location on a map. While testing the system, there were times where the car showed itself off of the road. After looking into it further, they learned the map maker had taken some liberties with the exact position of the road, and the vehicle was correct.
Previous discussion: https://news.ycombinator.com/item?id=38135979
Interestingly, if you have good map data, the relative "shape" of you previous trajectory is enough to locate your position globally, without GPS, even without knowing where north is.
https://ad-publications.informatik.uni-freiburg.de/GIS_paths...
Thank you for sharing this. I do work in this space and had not come across this before.
that's literally no different than what Google Maps does in my car while in CarPlay mode. It's like Apple neuters it and don't give it full gyro/compass data, because when driving it constantly moves the "car" anywhere from 90 to 270 degress and keeps it there for a few seconds until it figures this out again. I checked all possible permissions and still can't figure it out.
Never happens on the Apple Maps, although I have 0 trust in siri and apple maps, especially when we travel to europe, i feel like i'm an experiment for apple to see how much off straight forward route it can make me take.
I have the same thing happen on Google Maps - on top of my car just spinning in circles, it will also show up 100-300 feet to the right of the road I'm driving on, constantly doing navigation updates to the nearest street. When I unplug from carplay, it's fine, and back on the road, then when I plug it into the car it pops to the right again and starts doing updates.
Interesting. A number of years ago google maps on apple didn't behave that way. Then one trip I noticed my wife's maps were freaking out in a city with a lot of large curves and clover leaf onramps.
Of course my android with Google maps behaves as expected, though in a few places with stacked interchanges it can get confused if traffic is moving slow.
Not dead reckoning related but for some reason your comment made me think of this.
Map makers make mistakes on purpose. This way they know when someone copies their maps. They look for these little tiny "mistakes".
My favorite are the trap towns that didn't exist, but because of the maps with the trap towns on them a form of citogensis occurs and the town is bootstrapped into existence in the real world.
This seems like it's happening more and more with google maps. I see tons of "Trap Towns" and can't figure out of its realtors making up new neighborhood s to sell houses or them going on google maps, and putting google maps into reality.
My favourite example of some humorous dead reckoning, from this old copypasta:
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The missile knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is greater), it obtains a difference, or deviation. The guidance subsystem uses deviations to generate corrective commands to drive the missile from a position where it is to a position where it isn't, and arriving at a position where it wasn't, it now is. Consequently, the position where it is, is now the position that it wasn't, and it follows that the position that it was, is now the position that it isn't.
In the event that the position that it is in is not the position that it wasn't, the system has acquired a variation, the variation being the difference between where the missile is, and where it wasn't. If variation is considered to be a significant factor, it too may be corrected by the GEA. However, the missile must also know where it was. The missile guidance computer scenario works as follows. Because a variation has modified some of the information the missile has obtained, it is not sure just where it is. However, it is sure where it isn't, within reason, and it knows where it was. It now subtracts where it should be from where it wasn't, or vice-versa, and by differentiating this from the algebraic sum of where it shouldn't be, and where it was, it is able to obtain the deviation and its variation, which is called error.
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I think the delivery in this video is an important part of it: https://www.youtube.com/watch?v=bZe5J8SVCYQ
Someone put a beat behind it and it's now the source for an in-joke of "Missle Knows Where It Is Monday": https://youtu.be/6iBeRfOAAwk
Made me think of Doolittle philosophically provoking Bomb 20 in John Carpenter’s _Dark Star_. [0]
> the castaways had not seen any women in months, and based on the resulting unwanted attention, the indigenous people opted to evacuate before the English seamen became a problem.
chef kiss
Damn interesting has an amazing collection of high-quality podcast episodes with amazing story telling. They haven’t released new episodes in a while, but their back catalogue is worth investigating.
It bugs me that the last episode is ominously called "A trail gone cold", and I wonder what went wrong.
Alan Bellows here, author of this article, and founder of Damn Interesting. For years I kept the site going by working a part-time coding job, along with occasional contract work. Combined with donations to the site, this brought in enough income to survive, while allowing me to dedicate 5-6 hours per weekday to writing/editing/etc.
Early in the pandemic my job wrapped up, and when I went looking for a new part-time or contract gig, there was absolutely nothing. I networked and searched for a year and a half, and never found a single part-time opening. In the meantime, donations to the site were on a steady downward trajectory. I was burning through my savings at an alarming rate.
Eventually I had to take a regular full-time job just to have income again. I hoped I could find some plausible approach, but so far it's been unworkable. I also have a six year old, so evenings and weekends tend to be spoken for. And after the little one's bedtime, there's not much left in the fuel tanks. I'm approaching 50 now.
Maybe I'll find a part-time gig, or perhaps some anonymous wealthy benefactor will fund the site for a while. Both have happened before. If not, we may need to pack it up soon. 20 years is a pretty good run.
Dammit. Maybe some wealthy benefactor could give you a part-time job, at least, for the common good. What sort of coding?
Well, lots of kinds. I work a lot in front-end web dev, so I'm immersed in HTML, CSS/SCSS, Javascript, etc. Server-side, most of my experience is with PHP, but I've also worked with Python. I can code in Java, but I find it to be a joyless enterprise. At my current day job I mostly work with Perl, which is antique but charming.
My beard is getting gray enough that most tech places don't want me anymore, experience be damned. And my other skills (writing, editing, illustration, sound design, narration) are unlikely to earn me a living. It's an uncertain place to be.
Good to see you again, Alan. You might remember me from the Cellar many years ago. Your site is quite a treasure.
Oh hey Beestie! I don't know if you'll actually see this reply since it's belated, but alas. Thanks for saying nice words. I hope you are well. *cough*
What I find remarkable is the way the Admiralty - a very imperfect system with multiple facets that are downright clownish is nevertheless principled as a whole when it comes to strategic interests - the nation's foes are harassed, leadership positions are manned by technically competent individuals, regulations are amended to incorporate major learnings and so on.
Also, the banality of how the system treats sailor lives as expendable is almost incomprehensible from a 21st century perspective.
Notable for deadpan correct use of Ear regardless . . .
Worth the read.
Agreed, this article is well-written and rewarding to anyone capable of enjoying prose. Take the time to enjoy the article.
And for HN in particular, there is an ancestral link from the suffering crew of the ill-fated ship to the category of jobs that we have today.
I won't spoil it. But here is a clue: A.L.
Oh irregardless. Clever. I admire how Alan spins these puns up with such casual breeziness, but of course I would say that because I'm a big fan.
Spoiler alert! That was brilliant. I read it then went back and like "hold on...."
My favourite dead reckoning anecdote[1] was there was this British naval captain who found himself in the Atlantic just a bit south-west of the Canary Islands in a lifeboat. He knew that the ocean currents would be against him and too strong to row against, so he set off for South America and made it there by rowing with the current and using dead reckoning to course correct.
[1] And this is from memory and a bunch of googling around hasn’t turned it up so pardon me if I get some details wrong.
Badass. Thank you.
It's an incredible story and deserves to be told. 1500miles at sea in an overloaded open lifeboat using stellar navigation and managed to save more than half of the people aboard. So they were sailing rather than rowing but other than that I had remembered it substantially correctly.
Transatlantic by dead reckoning alone sounds impossibly difficult. Captain Bligh navigating 3500 nautical miles from Tahiti to Kupang in an open boat after being mutinied against was a celebrated feat of navigation, and he had the aid of a compass and a pocket watch.
So long as one can see the sun and stars reasonably frequently, I imagine a competent navigator could estimate his latitude and know which way is West accurately enough to stay in the trade winds and make landfall along Brazil's coast, which I suppose was McVicar's only hope, given the extreme shortage of water and rations.
I really enjoyed The Wager by David Grann about this story. Grann was also the author of Killers of the Flower Moon, which was made into the movie of the same name by Martin Scorsese, and Scorsese is now making The Wager into a film, although I don't think they've even settled on a release year yet.
The part about scurvy reminded me about the role scurvy played in Robert Falcon Scott's 1911 Antarctic expedition: https://idlewords.com/2010/03/scott_and_scurvy.htm
Reminds me of "In The Heart of the Sea: The Comedy of the Whaleship Essex" (a musical book report)
Amazing story. I read the book and couldn't put it down. Highly recommended.
If by 'the book' you are referring to David Gran's The Wager, it's worth noting that the article linked here (which I wrote) was published about 3 years before that book was published. I mention this only to dispel any impression that the article is derived from Gran's book.
Ah cool, I didn't know that. Sorry, I didn't intend to encourage that impression.
Incredible article really well done. Amazing story and was not expecting the connection to ada lovelace.
This is from (2019)
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This is a kind of batshit you really only find on this site. We should all marvel at it.
> i'm wondering whether Trump will surprisingly be vindicated by history
He won’t. And those that went along with him will be judged poorly by it.
> the Drake Passage was the least impractical route for large European ships to travel around South America to access its west coast.
"least impractical"?
Unintentional double negative, I think?
Currently it conveys the meaning of being "most practical" whereas it was the opposite.
It's correct and as intended. "Least impractical" denotes "most practical" but the double negative, which you accurately note is unusual but which is grammatical in this usage, calls attention to the specific connotation that all options are bad and this, though also bad, is nonetheless the most potentially serviceable of the lot.
We all know that language contains a lot of subtleties, but it is always interesting when someone breaks down exactly how those are used in some interesting prose.
And the prose itself is good too.
I've been an eager student of grammatical nuance in English since my introduction to the written language at age two. I'm always happy to take apart an example of same and show its workings!
I had to read that twice, but it’s correct I think. It’s an impractical route, but all the routes are… the Drake Passage was the least impractical of all of the routes.
Although I did wonder later on why they couldn't have gone through the Straits of Magellan on the journey west. Presumably it was even more difficult for large ships to navigate that narrow and presumably shallow passage.
At that time, the Straits of Magellan were “controlled” by Spain and it would have been extremely difficult to sail through undetected.
Plus, it’s like sailing through a maze where if you touch the wall you die. You really should have someone that’s been through it many times before. Even in modern times, they require local pilots to guide ships.
I read "least impractical" as meaning "least worst" -- the best bad option.