On Fri, Nov 22, 2019 at 9:01 AM Bob kb8tq <[email protected]> wrote: > > Hi > > At least right now, it is the “king of the hill” in terms of low cost modules > that > will do L1 / L2. > > If the target application is precision survey work, you do want (at least) > dual > band reception. All of the post processing outfits are looking for that sort > of data. > > I do not know of any free sites that will post process “L1 only” data. Without > post processing, you will not get mm level results.
The NRC Precise Point Positioning service (https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php?locale=en) will do L1 only but it seems to be the only one. Have used it successfully with ublox6 L1-only data and after waiting the 12-18 days for the Final GPS orbits to be available and resubmitting, it did improve the residuals considerably. It still won't be to the mm-level that you would get from dual frequency L1/L2 data of course. You probably don't need to wait that many days for the Final GPS satellite orbits; the IGS products page (https://www.igs.org/products)shows that even the real-time ultra-rapid products are a factor of 20x better in the orbit (but interestingly not the satellite clocks) than the broadcast ephemeris. But if you are trying to find small drifts over a year, rather than say doing real-time RTK corrections, you have the luxury of time to wait for the absolute best orbits before doing the processing. > > Indeed with any of these numbers you can wonder what the errors might really > be. If the claim is 5 mm, could it really be 8 mm? sure it could. If I > average L1 > data for a few days and think I’m at 500 mm could I really be over 800 mm off? > Yes, and I do have data on that. > > If you are after things like continental drift or wander of a post in the > ground, > you are after mm level numbers. > > Bob > Cheers, Tim _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
