What kind of absolute position accuracy is typical?

All field tests have been with a Topcon Hiper V base/rover kit vs the Emlid Reach RS+ base/rover kit. Our scenario is probably different than allot of you all because I (1) Do not have allot of trust in our CORS system after testing unless I post-process everything, (2) I need site acuracy and (3) The CORS system is not fast enough for our machine control. I think I will make this a disclaimer on my account as a little different of a user-base trying to push the Reach system or at least take it where it may not be intended.

Interesting scenario, I’ll try that soon!

What is your take on mechanical inaccuracies? I.e the levelling of rover-pole, threshold of a levelling bubble and so on?
I see a lot of images of people just hand-holding the rover-pole. Having tried that, and thus knowing how hard it is to keep that thing perfectly level for just 60 seconds, aren’t we then past 2-3 cm error quite quickly?

Yeah, that’s a big no-no and I highly encourage everyone to get get a rover pole with a tripod attachment for their base stations and a bipod for their rover. Don’t get me wrong, level tripods and a tribrach plus a mounting adapter are great, but for less cost you get an unmistakable, on-point, fixed height level in 30 seconds every time. Of course like anything else they need to be calibrated once every 6-months or so. I like the Seco yellow aluminum snap-lock poles. You can hunt around though and find better pricing.

https://www.tigersupplies.com/Products/Seco-Construction-Series-Thumb-Release-Tripod__SEC5218-40-FLY-.aspx

https://www.tigersupplies.com/Products/Seco-2m-Snap-Lock-Rover-Rod__SEC5125-20-YEL.aspx

https://www.tigersupplies.com/Products/Seco-Construction-Series-Thumb-Release-Bipod__SEC5217-40-FLY-.aspx

Further on the testing. I setup each base on known points and have a quick-lock setup for my rovers so I can push-button move them from my vehicle mounts to my rover pole. I drive to the point, take the Reach off the car, lock it to my rover pole, shoot it and while leaving the pole there do the same with the Hiper. The first time I tried this I was using magnet for the Hiper and Reachview for the RS+ and I thought I had just wasted my money because my elevation deltas were huge, but what I quickly relaized is that the Reach is a theoretical ellipsoid where as my Topcon was on a localized datum. I had 6 feet of error from the two! I used the NOAA site the try to transform from the ellipsoid to my GEOID and that was nonsense. It was much closer, but still not the same as the level-loop.

That’s also what I use (tripod for base and pole+bipod for rover).

So for the sake of making a proper comparison, how much time do you spend with the pole at center of the GCP?
2 components as I see it, levelling and measuring, placing and leveling taking 15-30 seconds and then the time spent collecting data in a now static environment. Is it roughly comparable with your time spent ?

Sorry to hijack the thread…

Car Mount - https://www.tigersupplies.com/Products/Seco-Single-Mag-Mount-with-Quick-Release-Tip__SEC5114-051.aspx (They also make a tri-magnet for rough conditions.)

Rover pole - https://www.tigersupplies.com/Products/GPS-Quick-Release-Adapter-(Leica)__ADI765-11.aspx

Rover - https://www.tigersupplies.com/Products/AdirPro-GPS-Quick-Disconnect-Adapter__ADI765-02.aspx

Leveling and placing not included, just the collection. I was trying for 2 minutes Emlid and my typical (don’t laugh) 3-second Topcon. I think I am not quite the normal user on this forum simply for the fact that I want to be relative and right on the ground inside the boundaries of my subject. Not the planet.

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All that being said, I totally support Emlid. I think it is an amazing product for the cost-point and if I can get it to do what i want it to do with our Magnet Field software with minor user training I will order 20 sets tomorrow.

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So in relative terms, you would expect 1.5 mm XYZ combined RMS from the topcon from a topcon multiband system with 3 seconds, if I understand you correctly ?

Correct, this is with a control system localized from control per the engineering plans which is shot in by a robotic total station and level-looped for elevations. Fairly typical construction process, at least in our company. Where my tolerance is and may be perceived differently is that anything more than 0.05’ deviation in the localization file is removed and my stakeouts can then be 0.05’, NEVER more than a tenth. If a control point checks in that bad then it was either mistakenly used or it has been disturbed. and is taken out of the localization after some checks. Usually 0.03-0.07’ is pretty typical for our primary control.

So 0.8-2.54 mm for us Europeans :smiley:

For the same 3 second obs time, what would you, with your experience of the system, expect of the reach ?
And for a 30 second obs time?

Good fix with the Reachview software 7cm and Magnet Software 5cm. RTK, no post-processing. The only place I really have trouble with the Reach, because of the single channel, is in our more hilly areas with medium vegetation.

so to standardise the test, would this flow be ok for a comparison:

  • initiate base (average single fine, as the test is about relative accuracy)
  • initate rover (note time when ready), kinematic RTK mode
  • start new survey
  • obtain fix (note time, note how long it took to fix AR > 3
  • walk to first GCP
  • place Rover rod and bipod on GCP
  • level setup
  • survey for 3 seconds
  • stop and save collection
  • survey for 40 seconds (Emlid recommended)
  • stop and save collection
  • survey for 3 mins
  • stop and save collection
  • place rover on next step and repeat the 3 individual measurements.
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Would it be best though to simulate a single collection, to move the rover then come pack to the GCP then do another collection? Isn’t the RTK running continuously so if you leveled the bipod (several seconds) made a 3 second collection, then after a few more seconds made a 40 second collection, wouldn’t the 40 second collection theoretically be more corrected than if you you made a 40 second collection as soon as you placed and leveled on the GCP since the rover would have been sitting on the GCP for longer if you are taking a succession of multiple collections at the same spot?

I was noticing with a good fix, that the RMSE numbers were the same (going to 3 decimal places) whether I collected 10 seconds or 1 minute. They didn’t go significantly up or down (I was working in pretty ideal conditions) so my thought was the 10 second collection (at least for my purpose not needing <3cm accuracy) was adequate and collecting any longer is following the law of diminishing returns on the accuracy over the extra time to survey multiple points.

Are you testing just the emlid or against another survey system? I think your outline looks pretty good. @jazee had a good point with walking away from it, but you’re test seems designed to prove that a longer collection time is more repeatable. That being said once you have collected your three points walk at least 10 meters away, sit for a second and then go back to the point and stake out each of the three points that you just collected. The longest point should be the most accurate, but if there is not a differentiation that exceeds your tolerance then you know on average what is safe to shoot. I would do this several times on different points.

I think for the accuracies that you are needing that with a good fix 60 seconds should be plenty.

@timmyd, have you shared the link to your video yet? Do you know the timestamp for the basic EZSurv run through?
If it is posted then I would encourage everyone to go look at the workflow for EZSurv. If your use-case is to make money then the bit that you spend on this program is a better choice than RTKLIB. Especially if you have more people than yourself that are going to be dealing with this data.

Hey Michael,
This is the link to the full “101” tutorial:

In the video there is an Index of the different sections and time stamps for each.

This is the basic video that I did which did not go into all the detail:

Let me know if this is not what you were looking for.

Tim

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The post processing part starts at 41:45 in the full 101 tutorial video.

I know a lot of people here steer away from EZSurv as the price is almost the same as a Reach Unit and most of us buying these Reach units are doing so because it fits our budget RTKLib therefore is more popular due to the low cost (nothing). I think RTKLib is perfectly fine though for people that have a very good technical knowledge of how PPK works and the various workflows using RTKLib.

The fact EZSurv states “you can also access automatically 10,000 base stations.” That’s sounds really nice and convenient to me. But then again, there’s a reason they teach you Algebra/Calculus/Geometry/Physics in school instead of just handing you a scientific calculator and/or CAD program that does all the calcs for you. It’s good to have an understanding of what the software is doing for you. Still, surveying is just a side interest for me as it infrequently pertains to a drone job from time to time. I don’t expect to have time to become an expert but being able to easily and quickly do my own PPK when necessary would be nice, hence I may fork out the money for EZSurv if the learning curve is signficantly easier than RTKLib. I guess it really boils down to a matter of budget and patience/time.