On Wed, Apr 25, 2018 at 8:38 AM, Tim Lister <[email protected]> wrote: > On Wed, Apr 25, 2018 at 7:56 AM, 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. > > Hi Tom, list, as another researcher who is also interested in > telescope positions (!) I have done this for personal use at home with > a ublox 6T and 53532A antenna to see what I got. I was logging in the > UBX binary format with the raw (carrier phase) measurements turned on > and then converting it to RINEX and using the NRC's CSRS-PPP online > service which is one of the few that will take single frequency L1 > only data. The results based on approx. 41.5 hours of data and which > were post-processed 21 days later (so that they used the IGS Final > products rather than the Rapids or Ultra Rapids) were Sigmas(95%) of > 0.105 m, 0.089 m, 0.217 m in latitude, longitude and ellipsoidal > height respectively. I was quite impressed with the results without > use of the L2 frequency to correct for the ionosphere etc.
It has taken me quite a bit longer that I had hoped but I have finally published a writeup and howto of collecting raw ublox data, converting it to RINEX and how to do (or get the NRC experts to do) the post-processing. It's at a new website I have setup: https://adventuresinprecision.space/howtos/precise-gps-positions/ Please let me know any comments or suggestions you have to improve it or make it more comprehensible and comprehensive. I have also been doing some experiments with RTK solutions with local precise base stations and receiving NTRIP correction messages over RTCM. This is looking very promising but I need to do some more experiments (and as detailed in the howto, wait for some more precise products to be available to compare it with...) Cheers, Tim _______________________________________________ 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.
