[time-nuts] nuts about position
Bob kb8tq
kb8tq at n1k.org
Thu Apr 26 08:42:58 EDT 2018
Hi
On something like a phone, you are likely looking at a combination of what the
phone does and a contribution from “the cloud”. Part of that cloud contribution
depends a bit on the carrier and how well they are doing their part of things. In
one area you might have surveyed towers and a full GPS / Glonass synthesis.
If you bought your service from Crazy Bob, there may be no local correction
information. Forget about GPS / Glonass in that case (at least in the US).
Bob
> On Apr 25, 2018, at 10:46 PM, Brooke Clarke <brooke at pacific.net> wrote:
>
> Hi J:
>
> I had a number of survey stakes I placed using a manual transit and tape measure and hired a local surveyor to tell me where they were and also tell me where my GPS antenna was located.
>
> He setup a GPS antenna on one tripod and a (Trimble?) combined GPS-total station on another tripod and ran a cable between the two. After some time (tens of minutes or ??) he used the theodolite to sight my stakes and the GPS antenna. I got a report back in a week or so. Total cost a few hundred dollars.
>
> I'm in the process of looking at how accurate the GPS is in my new LG G6 phone.
>
> --
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com
> http://www.end2partygovernment.com/2012Issues.html
>
> -------- Original Message --------
>> I think to really be confident about a position you really need the dual-frequency data (or that data from a nearby reference station), otherwise you could end up in a situation where you're consistent, but that consistency has a bias. IIRC, anyhow -- I'm not sure how the math actually works out.
>>
>> Anyhow, I play around with PPP stuff on occasion, and the last run I did was in November using the Novatel OEM628 kit that was briefly available for cheap on eBay, and the included 702-GG antenna (which, conveniently, has calibrations available). Running a day's worth of data through CSRS-PPP produced sigmas (95%) of 0.004m latitude, 0.008m longitude, and 0.024m in elevation. I've done some shorter runs since then that appear to fall in that same range ... I really need to do a few more full runs and see what kind of variance there is.
>>
>> At any rate, theoretically you can get ^^^ that close, anyhow. CSRS even takes solid earth tides into account, though I didn't do that because I was never able to figure out which specific type of solid earth tide data I needed. I imagine there's still some issues with any given datum being somewhat imperfect, as far as altitude is concerned, and I don't really know how to correctly deal with that if exact altitude matters. Maybe we should all just agree to use XYZ/ECEF coordinates for everything and give up on this whole altitude thing altogether... ;)
>>
>> (As an aside, I've been tempted to get someone to come professionally survey my antenna and tell me where it _actually_ is, so I could see how well I could actually do with my GPS kit, but I imagine it's pretty expensive -- anyone happen to know what getting that kind of thing done actually ends up costing?)
>>
>> -j
>
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