Today was the first time I collected GCPs with a dedicated base sending my RS3 rover corrections via Emlid Caster. Holy cow! 5mm accuracy? I’m shocked. Why is this so much more accurate than just a rover receiving RTK corrections with no base involved? I’m new so I’m asking. Thanks.
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Hi,
The RMS number isn’t accuracy, it’s actually the precision (spread) of all the differences in the positions the device is calculating…while it is where it thinks it should be…but may not be.
The RMS number is a statistical calculation telling you that 63% of the time the various positions calculated are spread about that distance. To be 95% confident you would use 2 x RMS which in this case would mean it thinks you should be within 1cm.
However, I say thinks because the real accuracy of that is really going to depend on how accurate your base coordinates are that you are measuring relative to.
For example, if your base point is known to within +/- 1cm, then you could be 95% confident you will be within +/- 1cm of +/- 1cm, so within 2cm.
If you don’t have an accurate known point, and a good set up and correctly enter all the parameters, then your accuracy will be that you can have a 95% level of confidence that you are +/- 1cm from…nowhere.
If you receive RTK corrections, they are still coming from a base. And the further it is away the more variability and therefore uncertainty comes into the equation.
This is largely because of increasing atmospheric effects that vary the signals, and all the obstructions around you that cause reflections (multipath) and therefore varying the measured signal distances to the receiver.
If the base is very close by then the atmospheric effects, and to some extent the reflections are the same to both of the receivers and cancel out.
Thats why RMS is one really good indicator of signal quality and how much to trust the position, and why for high accuracy work local bases are still used.
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Hi @petehernandez,
Good to see these values! RMS indeed refers to the quality of your data, but as Wombo also underlined, it’s different from accuracy. It’s rather about a range in which the true position is.
With Emlid Caster, you’re working with your own base, which means that the baseline is shorter than when connecting to a base station of an NTRIP service. And a shorter baseline will provide you with higher accuracy.
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Also, don’t forget optical plummet error if using a tripod/tribrachs. And rover rod bubble accuracy.
You can add approx 1-2 cm error if they are not in good adjustment.
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Good tip. I use a laser plummet
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We have two of the laser plummets. They are great but require adjustment also . We only use these indoors while layout of plant machinery.
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How do you varify if they’re off and if so, how do you adjust them?
This video is for adjusting an Optical system, but the principle is the same
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We have 2 Leica SNLL321 Nadir/Zenith Laser Plummet, they are not cheap. They are used for both vertical directions (up/down). Only used in industrial type work as described above.
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Learn… like the rest of us
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Try to be classier… like the rest of us.
Take it for what it is… learning is a process you do everyday in whatever you do.
I’ll help anyone who asks, but they have to show me they want to learn.
This coming from a 40 year licensed surveyor.
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Thanks for the info. I don’t have a total station but I’ll try to apply what I can…
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In GNSS, RMS error stands for Root Mean Square error, a statistical measure used to quantify the accuracy of GNSS positional data. It represents the square root of the average of the squares of the errors or deviations between the observed GNSS position and the true (or reference) position. It provides an overall measure of positional accuracy.
What were the baselines of the two tests? What constellations were being used for corrections?
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41K baseline, GPS, QZSS, BeilDou, GLONASS, Galileo
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Just noting one comment you made in the original post, you cannot run RTK without a base. You can have a base on the ground providing corrections via radio, a personal receiver casting or a network service.
Which scenario is that baseline for? And what was the baseline of the other solution? Regardless, 41km is further than I would push it.
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Actually, now that I remember, disregard the 41km baseline comment. I used my base and the rover (RTK enabled drone) was no further than 700ft. from the base which was getting correction from Emlid Caster service.
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Gotcha. So you had the base setup locally, but still using NTRIP. is there a reason you couldn’t use LoRa? Was the other scenario you mentioned a network service?
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Yes, Emlid Caster is a network service. Don’t think I can connect the drone controller to LoRa but I’ll check if that’s better than the Caster service. I also did local NTRIP which sets up the base as the RTK base station with no need for internet.
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Oh, ok. I thought we were talking about a base and rover. Same applies to a drone on baselines. We always run local NTRIP.
What processing software are you using?
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