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Comment by placesalt | Hacker News Reader

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Dunno who down-voted you - but what environment are you operating in? One of the claims for the Japanese system (you can see it in its orbital design) is that it specifically provides more opportunities for overhead signal coverage, increasing reliability/accuracy in mountainous and heavily urbanized (ie, skyscraper canyons) terrain.

That all being said, I'm also of the opinion that this is more of a defense play. QZSS has the nice property have using geosync/geostationary orbits - I'd imagine that makes ASAT work a bit harder.

> In peacetime, at least

That's a huge proviso given recent geo-politics (and the possible change of that premise may be why Japan is hedging).

* https://news.antiwar.com/2023/04/16/defense-official-confirm...

* https://gpsjam.org

GPS is shit in Japanese cities because of the angle. Read the article on QZSS.

In a place like Ginza or Shinjuku it can be really frustrating to navigate using GPS when you exit a station and your location is off by 20m and your compass is also wrong by 90 degrees (I guess because of all the steel buildings). I haven't read up on it in a while but I think local augmentation for GPS, including indoors in malls, etc will eventually arrive once we figure out how to provide it as a public service instead of a bunch of companies competing to make a proprietary services that serve location-based ads.

Isn't that essentially what we landed on with Wigle and the various wifi location engines?

GPS doesn't work in dense cities without specific corrections because it reflects off the buildings, which means you don't know how long a signal took to get to you.

QZSS helps but the receiver still has to be designed for this specific situation.

The majority of the population in japan just lived with bad GPS for the last 2 decades?

As have we, and much longer than that. It is only fairly recently that GPS broadcasts an accurate signal on non-military bands.

The military eventually gave up the idea of having people pay for satellites they can't actually use. Mainly because capitalism decided to give up, call the taxpayer investment wasted and stolen from the people, and just build a location network on the ground that's more accurate than GPS. The military now uses $450 hammers and toilet seats to steal from the people.

https://en.wikipedia.org/wiki/Assisted_GNSS

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