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Super-Accurate GPS Chips Coming to Smartphones in 2018

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Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#71

Post by mynewtb »

chii wrote: post #55
MertsA wrote: post #45

Earlier quoted context omitted.

>The military has better precision, only because they buy better hardware. That's not true. Military receivers can use the Y Code which is encrypted for military use only. There are some really fancy civilian receivers out there that can leverage Y code to a limited extent without knowing the encryption key but full accuracy is only possible on a military receiver that can decrypt and use the Y code.

is there any reason to be even more accurate than a 5 meter radius? I mean, if you are targeting a person in a building, i can't see why it has to be more accurate than that. Navigation of a drone that is less than 5 meters in size may require higher accuracy, i suppose...

Imagine pedestrian navigation. 5 meters (a rare, perfect accuracy) would place you in the center of a street instead of the sidewalk.

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#73

Post by mynewtb »

lhl wrote: post #34

If anyone works in the field, I'd be interested in how this dual signal (L1/L5) chip interacts with the RTK/CPGPS [1] (which improves accuracy down to 1-3cm already (at the cost of using multiple GPS units)). RTK is commonly used in survey drones, and kits are available for about $1K. [1] https://en.wikipedia.org/wiki/Real_Time_Kinematic

RTK is very limited in spatial range, you would need to place stations all over the place (would be great if telcom's base stations were doing that!).

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#74

Post by Moru »

jordanthoms wrote: post #41
forapurpose wrote: post #35

Earlier quoted context omitted.

> accuracy is very bad at times What makes anyone confident in the accuracy of wearable tracking devices? I haven't seen it verified and I wouldn't assume it: Accuracy is expensive, generally speaking, and few consumers will pay for it or even question it - how often have you heard someone mention it? Or, for example, have you wondered how accurate your simple bathroom scale is? I looked into it a little, wanting to…

I'm not sure what the value of a more accurate scale would be for a bathroom scale - your weight varies by far more than 100g just based on what you've eaten and how much water you've retained.

A guess: Two uncertain data points makes it even worse. If you can at least depend on the scale, the error is lower.

I tested our old Nintendo wii (or whatever it's called) balance board and so far it gives the same value every time I step on it. The value was also only 0.2 kg off from the doctors expensive scale.

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#75

Post by cnvogel »

throwaway613834 wrote: post #59
philipkglass wrote: post #20

Earlier quoted context omitted.

Nothing at all: http://www.aholme.co.uk/GPS/Main.htm

How do these folks do the math? Do they understand general relativity? Or do they just pull the equations from somewhere?

There is no general relativity involved in calculating your position. Solving for your position is basic geometry, if you want to have better resolution, have good model for the effects of the atmosphere on the radio waves.

http://www.aholme.co.uk/GPS/user_position_solution.pdf

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#76

Post by captainmuon »

MertsA wrote: post #45
deckar01 wrote: post #10

Earlier quoted context omitted.

Things have changed since the 90s. > In May 2000, at the direction of President Bill Clinton, the U.S. government ended its use of Selective Availability in order to make GPS more responsive to civil and commercial users worldwide. > The United States has no intent to ever use Selective Availability again. The military has better precision, only because they buy better hardware. Similar hardware is used in commercial…

>The military has better precision, only because they buy better hardware. That's not true. Military receivers can use the Y Code which is encrypted for military use only. There are some really fancy civilian receivers out there that can leverage Y code to a limited extent without knowing the encryption key but full accuracy is only possible on a military receiver that can decrypt and use the Y code.

By the way, has anybody tried to crack P(Y) code using a kind of "rainbow table"? (I'm not advocating that ofc, just curious...) I mean, it gets it's security because the parameters to its generating function are not known. But the function repeats after about a week, and presumely can't be changed due to the large numbers of legacy devices in the field. So you could just record the whole signal for a week (I did a back of the envelope calculation some time ago and it would be about a TB IIRC). Then just build some kind of index, and after recording a few seconds, you can find your position in the code, and syncronize to it.

Also, I've been wondering, how effective the old scheme with a secret military and a public code was - certainly an old GPS reciever shows up sometimes at a military surplus store. I wouldn't be surprized if enemy nations bought one of those, and extracted the secret parameters from the now quite old chips using modern technology.

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#77

Post by captainmuon »

gruez wrote: post #11
sgk284 wrote: post #8

Earlier quoted context omitted.

There's usually restrictions that kick in at certain altitudes and/or hardware restrictions if you're going over a certain speed. Depending on the source of signals used, the military can also just change the precision for civilian bands. But in times of peace / low threat levels, there's not a particular need to do so.

But that's client side right? What's preventing someone from implementing a GPS receiver using a SDR that doesn't have those restrictions?

Anecdotically, some chinese GPS chips for cell phones don't have those restrictions, but they maybe have others. The restrictions have become dubious anyway, as most nations who have that kind of rocket have the facilities to build GPS receivers (OK, I don't know about NK...).

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#78

Post by 6t6t6t6 »

chii wrote: post #55
MertsA wrote: post #45

Earlier quoted context omitted.

>The military has better precision, only because they buy better hardware. That's not true. Military receivers can use the Y Code which is encrypted for military use only. There are some really fancy civilian receivers out there that can leverage Y code to a limited extent without knowing the encryption key but full accuracy is only possible on a military receiver that can decrypt and use the Y code.

is there any reason to be even more accurate than a 5 meter radius? I mean, if you are targeting a person in a building, i can't see why it has to be more accurate than that. Navigation of a drone that is less than 5 meters in size may require higher accuracy, i suppose...

A problem that I usually have with Google Maps is that, when I am driving in (or next to) an elevated highway, the GPS usually does not know if I am in the highway or in the road beneath it.

Knowing the lane of the highway you are may be useful as well.

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#79

Post by icantdrive55 »

js2 wrote: post #40
dmckeon wrote: post #27

Down to 30cm - good! Now all we need is a GPS-enabled app for urban pedestrians that reminds them to look left or right just before they step off a curb into oncoming traffic.

As a runner I’d appreciate the corresponding app to remind drivers to look both ways before turning right.

I sometimes think DMV should require a coordination, or some kind of computer driving simulation test. I don't think a quick spin around the block weeds out the people who shouldn't be driving.

If you fail more than three times; you don't get a driver's license. Or, need to wait a few years, and reapply.

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#80

Post by throwaway613834 »

cnvogel wrote: post #75
throwaway613834 wrote: post #59

Earlier quoted context omitted.

How do these folks do the math? Do they understand general relativity? Or do they just pull the equations from somewhere?

There is no general relativity involved in calculating your position. Solving for your position is basic geometry, if you want to have better resolution, have good model for the effects of the atmosphere on the radio waves. http://www.aholme.co.uk/GPS/user_position_solution.pdf

Huh, is the whole thing a myth then? I'd definitely read that GR is necessary, but now that I'm searching I see mentions of it being a myth.
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