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Recent twts in reply to #iefub6q

One thing I’ve learned from locking down my Android phone (see #pknsrda):

The data for assisted GPS does not come from Google or, better yet, A PUBLIC SERVICE, but from a server hosted by the hardware manufacturer. Without regularly fetching fresh A-GPS data, the GPS performance is much worse (https://en.wikipedia.org/wiki/Assisted_GNSS).

This means that the hardware manufacturer has (more or less) direct control over whether I’m able to use GPS or not. This isn’t an Android setting, it’s buried deep within the device, no way to change the URL. If that manufacturer decides one day to cut me off, for whatever reason, or goes bankrupt or whatever, then I’ll have to buy a new phone.

And of course, this data transfer is encrypted as well, so I don’t know what my phone sends to those servers.

All this smartphone business is such a clusterfuck. I should have never bought one of those things.

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The GPS satellites transmit an almanac, a (coarse) list of all satellite positions:

https://www.e-education.psu.edu/geog862/node/1739

That’s apparently crucial for a low “time to first fix” and, as I understand it, that’s where A-GPS comes into play: Downloading this information from the satellites takes about 12.5 minutes, but downloading it via the internet (A-GPS) is much faster.

So the question is: How long is this data valid for? It’s a bit hard to find information on this … It looks like it’s valid for several weeks:

https://flysight.ca/wiki/index.php/Almanac_and_ephemeris

If true, it would mean the situation is much less dramatic than I thought. 😅 I go on a walk every couple of days and that gives the device more than enough time to download an updated almanac. So, I guess I should be fine without A-GPS if I regularly use (standard) GPS for an hour or so. 🤔

We’ll see. This might take a couple of months to find out. 😂

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@movq@www.uninformativ.de Well I used to have a handheld GPS device, probably before I lost most of my sight. I didn’t really feel that it took ~12m to get a fix, it was usually much faster. You may just find that all this A-GPS thing is all just bullshit anyway and just an excuse to collect and store your GPS location on some random web server that someone else owns 🤣

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@prologic I sure hope you’re right. 😅 I’d love nothing more than not having to rely on the internet for this. 🤞

(I clearly remember sitting in my car and waiting an eternity to get a fix, though. I’d regularly start the GPS device and then continue to load up my bags/stuff into the car because it took so long. 😅 Maybe it was just a shitty device, who knows …)

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Okay, GPS performance has degraded a lot over the last few days.

  • Time to first fix is a couple of minutes now, instead of 5-30 seconds.
  • Accuracy is reduced greatly, probably because the phone can one lock on to about 6-12 satellites, this used to be around 30 satellites.

In theory and under good conditions, you need 4 satellites to get a fix. But in reality, there are rarely “good conditions”, there are always buildings, hills, or trees nearby, so you need as many satellites as you can possibly get.

It’s not completely useless (yet), but it’s not great. I think I’m gonna lift some firewall restrictions. 🫤

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