Hi I just ran a quick test - a Ublox 6T was configured to output the RXM-RAW messages every second and logging for some 14 hours using U-Center. The .ubx-file was converted to RINEX using teqc.exe, and uplaoded to NrCAN PPP. NrCAN PPP will process single frequency observations and correct using ionospheric maps I *believe*. (If I am wrong, ignore this post!)
I also continously log observations from a Trimble NetRS dual frequency GPS receiver, hooked up to the same antenna. I trust the PPP-calculated position accuracy of this receiver to within low double digits to high single digit millimeters. (For comparison, the report from NrCAN gives a 95% error ellipse on the UBlox as semi-major: 2.494dm, semi-minor: 1.760dm. The corresponding numbers for the NetRS is semi-major: 1.245cm, semi-minor: 0.760cm - the reports are usually below 10 mm in both axis. Note difference in units.) Comparing the calculated ECEF coordinates from the ppp-results using Pythagoras gives me a distance of 76 cm - 53 cm if we simply ignore height. This is with a survey grade antenna in a good location. It might be possible to shrink this to 30 cm and still have confidence in the results, but I think it would not be easy. I would guess a lot more data would be required, and it is also possible that delaying processing until more accurate ionospheric maps are available could help. I will reprocess in a couple of days and see if theres much of a difference. Ole On Wed, Apr 25, 2018 at 4:56 PM, Tom Van Baak <[email protected]> wrote: > List -- I had a recent query by a researcher who would like to pinpoint > the location of his telescope(s) within 0.3 meters. Also (he must be a true > scientist) he wants to do this on-the-cheap. He may have timing > requirements as well, but that's another posting. > > So I toss the GPS question to the group. Surely some of you have crossed > the line from precise time to precise location? > > How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D > position? > > When we run our GPSDO in survey mode how accurate a position do we get > after an hour, or even 24 or 48 hours? And here I mean accurate, not > stable. Have any of you compared that self-reported, self-survey result > against an independently measured professional result or known benchmark? > > Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot > accuracy given enough time? > > If not, what improvement would -T models and RINEX-based web-service > post-processing provide? > > It that's still not close enough to 0.3 m, is one then forced to use more > expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to > achieve this level of precision? If so, how cheaply can one do this? Or is > the learning curve more expensive than just hiring an survey specialist to > make a one-time cm-level measurement for you? > > Something tells me 1 foot accuracy in position is possible and actually > easier than 1 ns accuracy in time. I'm hoping some of you can help > recommend solution(s) to the researcher's question or shed light on this > interesting challenge. > > Thanks, > /tvb > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
