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This is interesting. GPSes work poorly in downtown Chicago, so hopefully this will help improve things.

If only there was some kind of mechanism like differential GPS that can be used to correct the GPS signal in some generic way. I understand this is what AGPS is supposed to do but it doesn't seem to work in downtown Chicago.

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Uber clearly is willing to spend millions of dollars to get better GPS accuracy. It may only be a matter of time until corporations start launching their own constellations similar to QZSS. Japan has 3 or 4 QZSS satellites that are in a geosynchronous orbit that keeps them (mostly) directly over Japan. Since the satellites are almost straight up, there's less multipath error from the signal bouncing around between buildings.

Yes, Chicago is one of the toughest cities for GPS in the US.

Here's a peek into average building heights in downtown Chicago. Anywhere red, yellow, or orange we expect to have poor sky visibility. GLONASS being more popular has made Chicago slightly less challenging, before you could have trouble even seeing enough satellites to get a fix.

https://imgur.com/a/3bjiiRw

It gets even harder streets with like Lower Wacker Drive that are one deck below street level. There is almost no line of sight to any sats.

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