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Calculating position from raw GPS data (2017)

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Re: Calculating position from raw GPS data (2017)

#41

Post by johnwalkr »

patze wrote: post #11
namibj wrote: post #8

Android provides carrier phase access for a while now, and with that relative positioning between such devices in about the same neighborhood can be done with enough precision that you have to care about where in the device the GNSS antenna lurks. That alone isn't too fancy; it gets good once you throw in the accelerometer and gyroscope in each device. Because with that you get this not only in realtime, but also wit…

Sounds interesting! Does this approach work in indoor scenarios? Would you mind to provide some further links/papers to this topic?

GPS-denied navigation is the search term. It works well enough for driving through a tunnel, because eventually you get a known location to correct previous estimates. For a fully-indoor environment it's very difficult to get good results and the technique depends on the use-case.

"Indoor GPS" using bluetooth beacons is technically possible but the space is filled with proprietary protocols/apps that try to make money by serving ads. It unfortunately doesn't seem to be evolving into a more useful extension of google maps.

Re: Calculating position from raw GPS data (2017)

#42

Post by cmsj »

drfuchs wrote: post #27

Exercise for flat-earthers: how does the GPS mapping on your phone work, without satellites orbiting a spherical Earth? Show your work.

In my experience, flat earthers are not capable of the kind of rigorous enquiry that would allow them to even attempt to answer this.

Flat earth isn't a position arrived at by reason, it's one that is invariably reached by either confusion, or as a necessary consequence of some unshakable core belief (typically either an extremely literal reading of the bible, or a paranoid "everything official is a lie" delusion).

Re: Calculating position from raw GPS data (2017)

#43

Post by ragebol »

patze wrote: post #11
namibj wrote: post #8

Android provides carrier phase access for a while now, and with that relative positioning between such devices in about the same neighborhood can be done with enough precision that you have to care about where in the device the GNSS antenna lurks. That alone isn't too fancy; it gets good once you throw in the accelerometer and gyroscope in each device. Because with that you get this not only in realtime, but also wit…

Sounds interesting! Does this approach work in indoor scenarios? Would you mind to provide some further links/papers to this topic?

For indoor, there's UWB, ultra wide band. Can also use Bluetooth or even lights blinking at different (high, non-humanly-visible) frequencies to do indoor positioning.

Re: Calculating position from raw GPS data (2017)

#44

Post by yboris »

I came across a researcher working on collecting GPS data on aquatic creatures that only rarely (and for a short time) come to the surface. By recording raw data and post-processing, the power consumption and minimum duration of exposure to satellite signal are both drastically reduced (duration is under a second).

Re: Calculating position from raw GPS data (2017)

#45

Post by rich90usa »

AlexanderTheGr8 wrote: post #10
Jerrrrrrry wrote: post #6

Earlier quoted context omitted.

Just remember to intentionally handicap yourself as to not infringe upon ITAR restrictions.

Can you explain what you mean by that? The only thing I can think of is that GPS has 2 modes : one civilian and other military use. But military use-case uses encryption so civilians can't use that mode anyway.

I launched a high altitude balloon as part of a summer school program over a decade ago and we checked on edge cases. Off the shelf GPS are supposed to not work beyond a certain height 18,000 m and/or speed 515 m/s to be a barrier for use as a weapon. Some hardware treat that as AND; some treat that condition as OR. The term to look up is “CoCom Limits”.

Re: Calculating position from raw GPS data (2017)

#46

Post by ssl-3 »

cmsj wrote: post #39
askvictor wrote: post #28

Earlier quoted context omitted.

There was a guy in NZ (Bruce Simpson) who detailed on his blog how to make a DIY cruise missile. I think he got politely asked to stop doing so at some point.

BPS.Space on youtube is working on a DIY space-capable rocket and in a recent video he mentioned that he is not doing this as a tutorial and that his guidance system likely already wanders into ITAR territory, and thus he's self-censoring which parts he shares and which parts happen off-camera. Ultimately these kinds of regulations are fairly silly because a sufficiently determined smart person can recreate the cover…

Any sufficiently smart person can accomplish the same original work as any other sufficiently smart person.

But when the details of these things are published or otherwise made openly available, it doesn't take nearly as many smarts to duplicate these accomplishments.

Quite often, that's good: It's easy for a dullard like me to build a circuit or to re-use some clever assembler code when someone else has published it for my own tinkering around the house. In this way, it's a pretty great world to live in; it is often very simple to stand on the shoulders of giants and get some things done that I could probably never do on my own.

But sometimes, that's bad: We don't live in a perfect world. Enemies exist. Things like ITAR can't prevent a sufficiently smart person from doing anything, but they do make it a lot harder for them to get started.

Re: Calculating position from raw GPS data (2017)

#47

Post by zokier »

defrost wrote: post #24
dingody wrote: post #23

I heard that GPS is one of the few applications in daily life that needs to consider relativistic effects. So, the generated data must have already excluded these relativistic effects, right?

> So, the generated data must .. What generated data are you talking about and who was it generated by? If you mean the output of commercial GPS units, then yes, all manner of error inducing effects have been compensated for in post aquisition processing that generates output. This article is about raw GPS data .. which is a collection of raw data streamed from multiple satellites that then requires processing to gen…

from that link

> Moreover, the clocks on satellites don’t have to be explicitly slowed down to fix the cumulative relativistic speed-up of time. As part of their broadcasted message a satellite emits three coefficients that allow the receiver to correct for any offset or speed change of that satellite’s clock.

My understanding is that GPS satellites clocks are tuned to tick slow exactly to account for relativity.

For example this (https://www.nist.gov/publications/global-positioning-system-...) paper explicitly states:

> First, each GPS space vehicle (SV) clock is offset from its nominal rate by about -4.45x10^-10 (= -38 microseconds per day) to allow for the relativistic offsets between the differences between the SV and the ground. Of this -38 microseconds per day, about -45 are due to the gravitational potential difference between the SV at its mean distance and the earth's surface, and +7 to the mean SV speed, which is about 3.87 km/sec. To this mean correction, each receiver must add a term due to the eccentricity of the GPS orbit.

Re: Calculating position from raw GPS data (2017)

#48

Post by namibj »

slow_typist wrote: post #34
namibj wrote: post #8

Android provides carrier phase access for a while now, and with that relative positioning between such devices in about the same neighborhood can be done with enough precision that you have to care about where in the device the GNSS antenna lurks. That alone isn't too fancy; it gets good once you throw in the accelerometer and gyroscope in each device. Because with that you get this not only in realtime, but also wit…

Can‘t you? https://www.mouser.de/ProductDetail/u-blox/ZED-F9P-02B?qs=DP...

They are 114.62 USD each if you buy at least 100 of them. And you still need to add an active antenna and a good crystal. Considering those, this module is about 3x the price I asked.

Re: Calculating position from raw GPS data (2017)

#49

Post by namibj »

patze wrote: post #11
namibj wrote: post #8

Android provides carrier phase access for a while now, and with that relative positioning between such devices in about the same neighborhood can be done with enough precision that you have to care about where in the device the GNSS antenna lurks. That alone isn't too fancy; it gets good once you throw in the accelerometer and gyroscope in each device. Because with that you get this not only in realtime, but also wit…

Sounds interesting! Does this approach work in indoor scenarios? Would you mind to provide some further links/papers to this topic?

For indoor you will prefer UWB[0] where you can set up base stations yourself that offer a service pretty much like GNSS signals (i.e., you can passively receive them from 4+ base stations and turn those pseudoranges into a position, provided you are told where they are and kept updated about their clock drift relative to each other (e.g. by them listening to their neighbors and piggybacking 2-way-ranging sessions on top of the beacons they already broadcast, each offering the clock offset to their neighbors in the data payload of their own beacon)), with the added benefit that by using a shared-key CSPRNG to generate the bitstream of the ranging code instead of a fixed known sequence, you can get authenticated ranging where MITM attacks are limited to artificially inflating the range (i.e., a trigger of "has to be close enough to the door handle that e.g. a pair of cameras looking at the areas right in front of either side of the door have it in view" can't be faked with a wireless MITM).

There are some links/papers in the publications section[2] of [1].

[0]: https://www.firaconsortium.org/ [1]: https://developer.android.com/develop/sensors-and-location/s... [2]: https://developer.android.com/develop/sensors-and-location/s...

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