Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

IPhone 4S has GLONASS in addition to GPS

apple.com

Post reply on HN
Print view View original

51–60 of 95 posts

Re: IPhone 4S has GLONASS in addition to GPS

#51

Post by singular »

eps wrote: post #13
singular wrote: post #6

Earlier quoted context omitted.

though off-topic and a bit of an aside, at university (I did civ eng) I learnt that it was possible to get cm-levels of accuracy out of GPS through clever arrangement of multiple sensors (for e.g. measuring the movement of buildings due to subsidence, etc.) In fact I just found a wikipedia article all about it - http://en.wikipedia.org/wiki/GPS_augmentation :)

In mid 90s I worked for a company that developed combined GPS/GLONASS receiver and aimed specifically at high-precision measurement market. With clever math modeling and by letting a receiver rest on one spot for longer periods of time, e.g. 30 min, they could get the precision down to 3 mm (millimeters). And that's without A-GPS, purely through oversampling of satellite data.

It's funny you mention that, as I swear the professor said it could be done to accuracy of mm, but after reviewing the wikipedia articles I had concluded I misremembered. Perhaps not...

Re: IPhone 4S has GLONASS in addition to GPS

#52

Post by pauldino »

lhnn wrote: post #34

I don't see a reference to GLONASS in the sub's page. Edit: It angers me that high-ranking users abuse their priviledge to downvote. I'm making a legitimate point here; I don't see "GLONASS" or any reference to alternative GPS in that page. On Reddit, someone suggested that TIL links to Wikipedia should point to the specific information, not the whole article. It got >1000 upvotes. When I point out that there is no o…

Here's what I see, it's right by GPS http://cl.ly/3m0L152W3M3T1Q2V2J1L

Re: IPhone 4S has GLONASS in addition to GPS

#53

Post by maaku »

lhnn wrote: post #44
AdamTReineke wrote: post #41

Earlier quoted context omitted.

Ctrl+F -> GLONASS. It's there.

Assisted GPS Digital compass Wi-Fi Cellular I did a CTRL-F on GLONASS and no match is found. I said I did this in my edit... I'd take a screenshot, but I'm at work.

Where do you live? It's probably GPS-only for your region.

Re: IPhone 4S has GLONASS in addition to GPS

#54

Post by CWuestefeld »

lucaspiller wrote: post #21
dchest wrote: post #2

Precisions: * GPS: 2.00—8.76 m * GLONASS: 4.46—7.38 m * GPS+GLONASS: 2.37—4.65 m [citation needed] (source: http://en.wikipedia.org/wiki/GLONASS ).

Also from the same page: Some modern receivers are able to use both GLONASS and GPS satellites together, providing greatly improved coverage in urban canyons and giving a very fast time to fix due to over 50 satellites being available. In indoor, urban canyon or mountainous areas, accuracy can be greatly improved over using GPS alone. Is there any reason, other than the higher number of sources, why GPS+GLONASS is be…

In situations like the "urban canyon", where the problem is that only a small slice of sky is visible, I would think that the advantages of using both systems would only be marginal.

The most accurate GPS fix is had when the satellites you're seeing are widely separated in the sky. In the urban canyon, the problem isn't a lack of satellites, but the fact that you can only see those that happen to be in a narrow slice. And narrow slices are bad for constraining the solution to the equations.

The way I think about it is each satellite being used in the solution is like a rope tied to the satellite (where stretchiness of the rope is analogous to measurement error). Your GPS receiver can calculate your location to within the accuracy of how far you can move while keeping all ropes taut.

So if you had a fix from two satellites that are smack next to each other, you really don't have a fix any better than a single sat. If you've got two ropes at 180-degrees opposite each other (i.e., at either end of the street in the urban canyon), you've still got ambiguity due to your potential for lateral movement. For a good fix, you've got to bring in another rope at a wide angle from those -- but the tall buildings interfere with getting that rope, even if there are lots of satellites up there that could be offering it.

Re: IPhone 4S has GLONASS in addition to GPS

#55

Post by SoupIce »

ConstantineXVI wrote: post #43
hackermom wrote: post #9

Related: the two first Galileo satellites ( http://en.wikipedia.org/wiki/Galileo_(satellite_navigation) ) will be launched tomorrow. The claimed precision of the free-for-all service is as granular as 1 meter, with the military/commercial service claiming to reach centimeter precision. I wonder when this shows up in smartphones.

Wonder how feasible it would be to have a single GPS+GLONASS+Galileo chip that automatically feeds you the service(s) with the best signal; without murdering your battery?

Why not interpolate the responses from GPS+GLONASS and come down to 10-20cm granularity?

Re: IPhone 4S has GLONASS in addition to GPS

#56

Post by ghshephard »

singular wrote: post #6
dchest wrote: post #2

Precisions: * GPS: 2.00—8.76 m * GLONASS: 4.46—7.38 m * GPS+GLONASS: 2.37—4.65 m [citation needed] (source: http://en.wikipedia.org/wiki/GLONASS ).

though off-topic and a bit of an aside, at university (I did civ eng) I learnt that it was possible to get cm-levels of accuracy out of GPS through clever arrangement of multiple sensors (for e.g. measuring the movement of buildings due to subsidence, etc.) In fact I just found a wikipedia article all about it - http://en.wikipedia.org/wiki/GPS_augmentation :)

In 1995 I worked for a GPS developer, Avcan Avionics, and we built software that would allow tundra devices in the Arctic to travel between a supply depot and remote mines in 100% whiteout conditions, navigating only by a path that had been loaded into GPS. Our variant of this process was called "Differential GPS" - basically leaving a base station in single location for 24+ Hours where it would eliminate the S/A error which was presumably random.

We successfully navigated a car down a twisting road, about 10' wide, without looking out the window, so it was a useful mechanism. It became less important, of course, once the US Government removed the S/A error from the GPS signal and the commercial use of GPS took off.

Re: IPhone 4S has GLONASS in addition to GPS

#57

Post by dchest »

lhnn wrote: post #34

I don't see a reference to GLONASS in the sub's page. Edit: It angers me that high-ranking users abuse their priviledge to downvote. I'm making a legitimate point here; I don't see "GLONASS" or any reference to alternative GPS in that page. On Reddit, someone suggested that TIL links to Wikipedia should point to the specific information, not the whole article. It got >1000 upvotes. When I point out that there is no o…

Sorry, there was no way to have a link to the related section on this page.

Re: IPhone 4S has GLONASS in addition to GPS

#58

Post by mdasen »

ConstantineXVI wrote: post #43
hackermom wrote: post #9

Related: the two first Galileo satellites ( http://en.wikipedia.org/wiki/Galileo_(satellite_navigation) ) will be launched tomorrow. The claimed precision of the free-for-all service is as granular as 1 meter, with the military/commercial service claiming to reach centimeter precision. I wonder when this shows up in smartphones.

Wonder how feasible it would be to have a single GPS+GLONASS+Galileo chip that automatically feeds you the service(s) with the best signal; without murdering your battery?

http://en.wikipedia.org/wiki/GLONASS#Accuracy

There are already chips that combine the results from GPS and GLONASS. Because it moves from 31 satellites to about 50, time to get a fix is improved (since it might see 4 GPS satellites and 2 GLONASS ones more easily) and accuracy is better.

Re: IPhone 4S has GLONASS in addition to GPS

#59

Post by Shenglong »

singular wrote: post #6
dchest wrote: post #2

Precisions: * GPS: 2.00—8.76 m * GLONASS: 4.46—7.38 m * GPS+GLONASS: 2.37—4.65 m [citation needed] (source: http://en.wikipedia.org/wiki/GLONASS ).

though off-topic and a bit of an aside, at university (I did civ eng) I learnt that it was possible to get cm-levels of accuracy out of GPS through clever arrangement of multiple sensors (for e.g. measuring the movement of buildings due to subsidence, etc.) In fact I just found a wikipedia article all about it - http://en.wikipedia.org/wiki/GPS_augmentation :)

I know carrier phase differential GPS is used on satellites to get amazing accuracy. I'm not quite sure what the implications are on mobile phones.

Re: IPhone 4S has GLONASS in addition to GPS

#60

Post by jdietrich »

dchest wrote: post #2

Precisions: * GPS: 2.00—8.76 m * GLONASS: 4.46—7.38 m * GPS+GLONASS: 2.37—4.65 m [citation needed] (source: http://en.wikipedia.org/wiki/GLONASS ).

Raw precision is only part of the story. GPS + GLONASS provides a number of significant practical advantages over GPS alone, mainly due to the increased number of satellites.

Performance in urban canyons or heavily wooded areas is greatly improved, as there's a much better chance of the receiver seeing enough satellites. Likewise, startup times can be much quicker.

An intelligent receiver using GLONASS only when needed could have dramatically better real-world performance with only a minor increase in battery consumption.

We're inevitably going to see GLONASS everywhere due to the Russian import duty, but it's a real boon to most ordinary GNSS users, for whom the main limit on practical precision is being able to see enough satellites. This is likely to become increasingly important as the existing GPS satellites reach end-of-life.

Post reply on HN