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Rethinking GPS: Engineering next-gen location at Uber (2018)

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Re: Rethinking GPS: Engineering next-gen location at Uber (2018)

#11

Post by AlotOfReading »

tuananh wrote: post #3

"2018" post.

I didn't even notice the date, thanks. The article presents it as if it was invented at Uber, but there's an identical family of techniques also called "shadow-matching" that have been known in the literature for like a decade. Many companies improve the raw GNSS fix with things like map-matching nowadays, but it was much less common even 5 years ago so this would have been fairly innovative back then.

Re: Rethinking GPS: Engineering next-gen location at Uber (2018)

#12

Post by skzv »

KMnO4 wrote: post #6

Cool, so it looks like they take the “raw” GPS location (after the GPS module does processing to spit out a lat/long) and applies statistical methods with a model of the actual 3D geometry. Seems like a smart way to improve the accuracy from “userspace”. This reminds me of the Comma.ai project, Laika [0]. Since they have access to the raw GPS module data (Ie the actual timings of each received satellite transmitting)…

You may be interested in knowing that Android has exposed raw GNSS measurements through public APIs [0,1] so anybody can build their own raw processing engines using techniques like the ones described in the article

[0] https://developer.android.com/guide/topics/sensors/gnss

[1] https://developer.android.com/reference/android/location/Gns...

Re: Rethinking GPS: Engineering next-gen location at Uber (2018)

#13

Post by LeoPanthera »

azinman2 wrote: post #8
c_o_n_v_e_x wrote: post #7

L5 GPS will address the multipath-in-urban-canyon problem that Uber worked on.

I don’t know much about L5. How does it do so?

To oversimplify: It's on a different frequency and so will be subject to different forms of error. You can average the results of L1 and L5 to get a more accurate position.

Re: Rethinking GPS: Engineering next-gen location at Uber (2018)

#14

Post by skzv »

azinman2 wrote: post #8
c_o_n_v_e_x wrote: post #7

L5 GPS will address the multipath-in-urban-canyon problem that Uber worked on.

I don’t know much about L5. How does it do so?

It has a shorter wavelength so the correlation peaks are more narrow and hence more easily distinguishable. See this illustration [0] taken from this article [1]

[0] https://insidegnss-com.exactdn.com/wp-content/uploads/2021/0...

[1] https://insidegnss.com/end-game-for-urban-gnss-googles-use-o...

Re: Rethinking GPS: Engineering next-gen location at Uber (2018)

#15

Post by ehsankia »

skzv wrote: post #10

Google explores these techniques as well. They're critical to improving accuracy in urban areas where you don't have line of sight to satellites (this is why your GNSS (AKA GPS) location is terrible whenever you're in a city). Here's [0] a cool gif visualizing the principle of GNSS ray tracing taken from one of Google's blog posts [1]. Here's an article with more information about Google's techniques [2]. [0] https:/…

That seems much more useful, since it applies to all Android apps, whereas Uber's solution would be limited to their app only.

Re: Rethinking GPS: Engineering next-gen location at Uber (2018)

#16

Post by skzv »

LeoPanthera wrote: post #13
azinman2 wrote: post #8

Earlier quoted context omitted.

I don’t know much about L5. How does it do so?

To oversimplify: It's on a different frequency and so will be subject to different forms of error. You can average the results of L1 and L5 to get a more accurate position.

Not just that. It's a higher frequency so the correlation peaks are more narrow and hence more easily distinguishable than L1 frequency

Re: Rethinking GPS: Engineering next-gen location at Uber (2018)

#19

Post by ilaksh »

skzv wrote: post #10

Google explores these techniques as well. They're critical to improving accuracy in urban areas where you don't have line of sight to satellites (this is why your GNSS (AKA GPS) location is terrible whenever you're in a city). Here's [0] a cool gif visualizing the principle of GNSS ray tracing taken from one of Google's blog posts [1]. Here's an article with more information about Google's techniques [2]. [0] https:/…

I think it says that FLP (Fused Location Provider) is not built in to Android.
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