 If you live in a city with tall buildings, take a look at the night skyline. The buildings probably have flashing lights on them to help aircraft pilots to identify the shapes of buildings and not fly into them. You might notice that the buildings flash in synchrony, even though they are hundreds of metres apart. What's going on? (continued) 41 comments
@ajft Pretty sure you were among the detective group that found the pattern in the first place. Now you can buy a beacon like this one, which is standalone and has a GPS receiver in it. Anyone who's cobbled together an NTP server will know that the GPS system can provide microsecond-accurate time as a side-effect. So these beacons don't care where they are, but they all know exactly when "now" is. And they can synchronize to each other by synchronizing to the GPS signal. It makes maintenance _so_ easy.  @futzle ... come to thisk of it, with GPS being GPS, that... might almost be how that fucker works  @ellenor2000 @futzle  @ellenor2000 @futzle this is basically true. With enough satelites, you have enough equations of location that you can solve for time (Postscript: a few of us here on the Fedi worked this out from first principles after someone noticed that the lights on several buildings in their city were all blinking together. It was a great piece of detective work.)  @futzle hi yes hello I was part of an art project that made use of this idea and I think of it every time I see groups of blinky lights ^_^ https://www.kickstarter.com/projects/966222131/straightedge-a-new-way-to-see-your-planet/description we ended up building our own lights and controllers and firmware for it, mostly because they would also - about every 10 minutes - display the speed of a seismic wave thru that particular soil geology https://github.com/ArdentHeavyIndustries/straightedge-gps-firmware   @bouncinglime @futzle That sounds awesome. Itβs hard for me to find photos/videos of the finished piece; would you happen to have any?  @bouncinglime Wow this is so cool! I'd heard about some of your projects before but not this one. Wish I'd been there to see it! @nyankat thanks! it was one of the coolest things I've ever been part of honestly π and yeah definitely one of those "you had to be there" types @futzle Thankyou for explaining this! I've tried to take photos of the Melbourne CBD skyline at night and noticed that many of the buildings have rooftop navigation lights in synch, a few switch with the same period but a different part of the cycle, and a few others appear to drift over time so they appear to harmonise sometimes but not at other times. @futzle This is a wonderful dive into something really interesting π Thank you I worked on systems which mass monitor extremely large amounts (>XX% of the total market in the US) of beacons. This synchronization caused issues (outages, slowness, downstream issues) at one point because they all happen at the same time in a geographic location, and a mass influx of updates come in then. It's quite interesting stuff and that is still one of the cooler projects I've built from the ground up :) @futzle  @futzle Very interesting thread! I can't help but wonder: if they have GPS, they not only sync but can also get coordinates of their location, ignoring height. So assuming resolution of <10meters and assuming buildings are usually >=5meters wide in any direction and have some space between them, wouldn't it be trivial to use the beacon's location as a seed to sync up all the lights of a building but ensure they are different from the beacons of the buildings next to them? @jorgeyanesdiez I can't think of a way to do this without the beacon needing to have a copy of a map. Consider in a dense downtown: the corners of different skyscrapers may be across a street only 20 m wide but the buildings themselves fill a 200 m block. Closeness is actually the _opposite_ of what you want. @futzle Nobody building the lights thought to put some kind of random jitter around the timings? @cratermoon How do you ensure that the ten lights you bought today for your new building all have the same jitter? Safest to engineer out that opportunity for user error. @futzle Ah, I see, I didn't understand how multiple beacons/building should work, thanks for clarifying. @futzle@old.mermaid.town This is super interesting. I'm a certified pilot, and I've never heard about these flashing patterns before!  @futzle Oh, fascinating. I'd noticed this synchronization with things like AM broadcast antenna tower arrays before, which maybe is a lot like a single building conceptually, but I hadn't noticed city skylines in recent years.  @weaselx86 Thank goodness buildings are built on a grid 131072 to the degree! π But seriously, they are already made with customizable blink timing patterns, but the fact that you see entire cities blinking like one giant Christmas tree tells you how much this feature is being used. @futzle Saying "bottom bits" was cavalier of the details; but the GPS has the location, and I'm confident it's possible to develop a location-based algorithm that could distinguish buildings reasonably well without requiring they be build on a grid. It seems like the manufacturers could improve the situation without cooperation from the field. @futzle similarly, back before GPS, radio altimeters, etc, if two flights were accidentally assigned to the same flight level, differences in their barometric altimeters meant they would probably miss each other even if they got quite close. So after the tech advances, everything is right at the altitude itβs been put at and the danger of collision went up for a while. Thatβs fixed now, but only because they built an entire traffic avoidance system to avoid this (TCAS)   @futzle |
Gregory's Server
@futzle ooo ooo, I know this one.... or I did. can remember reading up on it