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Re: RTK Base and its accuracy
From: |
Gary E. Miller |
Subject: |
Re: RTK Base and its accuracy |
Date: |
Tue, 16 Aug 2022 12:41:56 -0700 |
Yo Florian!
On Tue, 16 Aug 2022 09:25:48 +0200
Florian Kiera <florian.kiera@logicway.de> wrote:
> Hello Gary!
>
> Am 11.08.22 um 21:42 schrieb Gary E. Miller:
> > Yo Florian!
> >
> > On Wed, 10 Aug 2022 10:49:24 +0200
> > Florian Kiera <florian.kiera@logicway.de> wrote:
> >
> >>> Which are not precise enough for what you are doing. Just look at
> >>> what cgps is telling you. That is much more "precIse" than some
> >>> random wiebdite.
> >> That pretty much seems to be the issue already... the internet
> >> translators seem to have some issues with calculating the latitude
> >> correctly. cgps worked fine and gave the expected position.
> > Then you missed my point. They can all be correct, and different.
>
> Yet they calculated Latitude somehow "wrongly". (wrong by multiple
> kilometers) I understood that it can have some deviations. Still I
> would expect them to be in a meter scale and not kilometer. I would
> like to stick with the fact that cgps does it right and I am happy to
> use it.
There are USGS grid scales that differ by up to 3 meters. My
expectations are not as optimistic as yours. If gpsd, by way of cgps,
works for you, great. cgps does not cumpte anything, it just passes on
what gpsd tells it.
>
> >
> >>>> Latitude: 53.59931 11.41833
> >>> Determined how?
> >> With the position of the rover.
> > I don't think you understood my question. How do you know the
> > "accurate" position of the rover?
> Using a map. It can either be OpenStreetMaps or Google Maps. Both end
> up in the same spot (roughly where our "repeater source antenna" is
> positioned) with the Lat/Long I provided. Also the base has nearly
> the same coordinates as the base-antenna is close to the
> rover-repeater antenna.
There you go. That is what "repeaters" do, they repeat what the repeater
sees. Not good for precision work.
> >> Considering the base was not that wrong after all we can go back to
> >> the RTK base-rover scenario.
> > How wrong? How do you know how wrong?
> cgps gave the right position and therefore hardly can produce
> gibberish RTMC3.
Ah, lost me. cgps has no effect on the RTCM3 from your base.
RTCM3 is gibberish by design...
> A right position is determined in my opinion by
> taking the Lat/Long to a map and actually end up in the position
> where I actually stand at.
Google maps are not known for their accuracy. Go find a benchmrk.
And the accuracy varies minute by minute, so you need to run gpsprof
for many hours to determine your real performance.
> In this scenario I expect Lat/Long values
> which when used on a map end up close to where the antennas (base
> antenna and gps repeater antenna for the rover) are positioned on the
> roof.
We already agree your repeater is messing up your measurements, and yet
you still use it?
> >> I start the survey-in as described in
> >> the first mail and than start str2str from the RTKLib to push the
> >> RTCM3 messages to the running ntripcaster.
> > Which can work, but there are easier wasys to get the same retuls.
> Is it documented? I would always prefer easier ways when they produce
> the same outcome. We do want to use a NTRIP caster tho.
Not docuemnted by gpsd, but it should be in the u-blox manuals. Just
read the raw RTCM3 from the base, and nectcat (nc) it to the rover.
That is what most do for short range stuff.
> >>> The latitude
> >> on the rover was accurate but the longitude was a bit off (~20m).
> > Once again, you do not use "accurate" propertly. I'm guessing your
> > repeater antenna is 20 m away?
>
> I understand that the position of the repeater is "repeated". So the
> rover should think it is at the position of the gps repeater antenna.
Sort of. There are other effects in play. Too many to correct for.
> The antenna is like 4m above and 5m in a horizontal direction away.
> The offset probably comes from the fact that the rover antenna
> obtains values not only from the repeater but from outside the
> building as well.
Yeah, that will royally confuse your rover. I have played with
feeding 2 antennas into one GPS, The results are not pretty.
> The offset actually goes in the direction of the
> windows. (shortest way inside the building) The rover thinks it is
> 20m outside the building in that direction while it *should* think
> its on the roof of the building.
Then maybe you need to rethink "should" considering your data does not
match your expectations.
> We are going to test the rover outside the building soon and
> hopefully receive what we expected all along.
Hopefully.
> >> I
> >> used the latitude and longitude that gpsd gave out in google maps
> >> which gave me the visual offset on the map.
> > Not exactly a high precision method.
>
> If the Lat/Long isnt precise/accurate enough to be used on a map what
> are they for then?
Depends on what you need. If you are +/- 3 meters off 10% of the time,
then that is perfectly good o navigate a ship or fly an airplane. It is
not good enough to driave a car in a lane.
You need to quantify what you actually need. Then run tests, like with
gpsprof, to see what you are actually getting. Very few initially
expect how bad a GPS position can be 2% of the time.
> Simply imagining where I am? This is not about a
> single meter.
Getting under a meter with 8-series will be very hard, and certainly not
with a repeater invovled. Your own data tells you this.
> >> I will add the output.
> > Looking forward to it. Be sure to run gpsprof for at least 12
> > hours.
>
> I will run gpsprof today. I already added the output of the "simple",
> probably wrong, gpsprof run to my last email tho.
Sorry, if it was there, I missed it. Dunno what you mean by "simple".
Unless it runs modulo 12 hours, the data will be misleading.
RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588
Veritas liberabit vos. -- Quid est veritas?
"If you can't measure it, you can't improve it." - Lord Kelvin
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- RTK Base and its accuracy, Florian Kiera, 2022/08/09
- Re: RTK Base and its accuracy, Florian Kiera, 2022/08/09
- Re: RTK Base and its accuracy, Greg Troxel, 2022/08/09
- Re: RTK Base and its accuracy, Gary E. Miller, 2022/08/09
- Re: RTK Base and its accuracy, Florian Kiera, 2022/08/10
- Re: RTK Base and its accuracy, Gary E. Miller, 2022/08/11
- Re: RTK Base and its accuracy, Gary E. Miller, 2022/08/11
- Re: RTK Base and its accuracy, Florian Kiera, 2022/08/16
- Re: RTK Base and its accuracy,
Gary E. Miller <=
- Re: RTK Base and its accuracy, Florian Kiera, 2022/08/18
- Re: RTK Base and its accuracy, Gary E. Miller, 2022/08/18
- Re: RTK Base and its accuracy, Stéphane Péneau, 2022/08/21
Re: RTK Base and its accuracy, Gary E. Miller, 2022/08/09