
Rethinking GPS: Engineering Next-Gen Location at Uber - mpweiher
https://eng.uber.com/rethinking-gps/
======
jsnell
Previous discussion:
[https://news.ycombinator.com/item?id=16887276](https://news.ycombinator.com/item?id=16887276)

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rayiner
A big problem with Uber/Lyft is that drivers take all these fancy calculated
positions and plug them into a standard navigation app, which can direct the
driver to the completely wrong side of a large block. (Addresses are not very
granular in a city.) It’s interesting to me why Uber/Lyft allow this.

~~~
crunchlibrarian
There's also the fact that Google Map data is just flat out wrong in many
places in the middle of the country, it says my house is my neighbor's house
and so on down the block, everyone is off by one.

I have tried to contact Google and get this fixed at least a dozen times over
the past decade, always ignored. They used to have a whole community mapping
thing where you could submit issues with the map, but those apparently are
ignored.

It's a real nightmare trying to convince the insurance company and local
government that google is wrong, love how that's my responsibility too.

~~~
ryandrake
It's funny, because out of the things that people complain about in modern
navigation apps, "showing the right user location" is usually not that high on
the list. There are so many other more pressing problems to solve. Map data is
often inaccurate, bordering on unusable in less populated areas, and map data
providers are colossally slow to update and correct their data. Navigation app
UI is still surprisingly bad, even though this has been an area of fierce
competition for at least a decade. Geocoding and reverse geocoding is still
not perfect, but it's dependent on good map data. Accurate traffic is hard.
Routing is pretty much solved but again, dependent on good map and traffic
data, so it's perceived as needing improvement. Business search is hard
because the underlying data changes so often, and for most nav system vendors,
is not their core business so they ship something crappy. Most of these things
are not improved by getting slightly better user position, so it's surprising
Uber is investing so much into this research.

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souterrain
> The use of particle filters necessitates a level of server affinity. Each
> new request to our service must be routed to the same back-end server for
> processing in order to update the correct particle filter.

Was implementing this on the client device considered? What were the
motivations for this design?

~~~
ryandrake
My guess is a combination of the following:

1\. Building 3D data is too large or inconvenient to store on the device.

2\. Continuously downloading/caching small localized chunks of that data would
result in unacceptable use of bandwidth for customers with limited data plans.

3\. Their implementation of the algorithm may be CPU inefficient and
contribute to excessive battery drain.

4\. (cynical) This gives them yet another excuse to be sucking up and storing
1Hz precise user location data, potentially to use for other reasons...

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karambahh
Why do they need a 3d map to begin with?

Following their example of which side of the canyon the phone is, given the
snr of sat b,c,d they can guess the side of the street.

If it's possible then being shadowed by an actual building, a construction
site or a delivery truck amounts to the same result (but I guess the snr would
vary between these 3 situations). Hence, why the need for the 3d model?

~~~
chinathrow
Long term thinking?

[https://www.wired.com/story/uber-unveils-flying-
taxi/](https://www.wired.com/story/uber-unveils-flying-taxi/)

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cdetrio
Any update on those new super-accurate GPS chips? [1]

1\.
[https://news.ycombinator.com/item?id=15308771](https://news.ycombinator.com/item?id=15308771)
Super-Accurate GPS Chips Coming to Smartphones in 2018 (ieee.org)

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0xmohit
Amusing that they don't mention that they're able to better predict your
location because of your phone's Wi-Fi.

Tracking people is _necessary_ [0] as Uber needs to _provide better services_.

[0]
[https://www.npr.org/sections/alltechconsidered/2016/12/01/50...](https://www.npr.org/sections/alltechconsidered/2016/12/01/503985473/uber-
now-tracks-passengers-locations-even-after-theyre-dropped-off)

~~~
ryandrake
Any competent phone manufacturer is already using Wi-Fi (and other input
signals) to assist GPS, and providing the improved output to apps. So, if Uber
is collecting Wi-Fi data, I doubt it's for the purpose of improving location.

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occams_chainsaw
Is this why Uber frequently pins me as being pretty far off from my actual
position, even when something like Google maps is showing the correct
position?

I mostly use Lyft now because I was tired of fighting with the Uber app to get
it to show my correct location

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catcow
I wonder why we don't have GPS transmitters installed at the top corners of
every tall building. Seems to me like this would be a pretty straightforward
solution in urban areas.

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angrygoat
tl;dr using 3D maps to build a model of GPS shadows for receiver and satellite
locations, and using the relative signal strength for each satellite, plus
that model, to come up with a more accurate receiver location.

Original UCSB site: [https://tia.ucsb.edu/about-tia/success-
stories/shadowmaps/](https://tia.ucsb.edu/about-tia/success-
stories/shadowmaps/)

A more detailed writeup by the original authors:
[http://insidegnss.com/auto/sepoct15-MADHOW_0.pdf](http://insidegnss.com/auto/sepoct15-MADHOW_0.pdf)

