[time-nuts] nuts about position

Brooke Clarke brooke at pacific.net
Wed Apr 25 22:46:01 EDT 2018

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

-------- 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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