Activity Feed › Discussion Forums › Strictly Surveying › Elevations – RTK vs Levelled
-
Thanks for sharing – would also be interesting to know the firmware version you were using. I have had some very good results with Captivates v7.50 firmware with and without multipath reduction.
Best regards,
Terry
-
@toivo1037 A 1/4 inch off of grade stakes is pretty optimistic from the contractor, but most operators I’ve known can certainly do much better than a tenth of a foot when they’ve been working off grade stakes. They also often had a grade checker who used the grade stakes to double check as they went through the site resulting in no/minimal need for blue tops (because the grade stakes were set with some care initially). Might be a temporal (as I haven’t done layout in years) or regional (I’ve read many different techniques employed elsewhere on the message boards over the years) difference.
In the situation I posted, the contractor was looking at three stakes with a dip in the middle of almost 0.16 of a foot (± an inch). Telling someone this is a constant grade when it isn’t marked that way doesn’t pass muster when the guy looking at the stakes has done that work all his life and can see that it is not.
Does it matter in the whole scheme of life – probably not. But I would wager money (and I’m a cheapskate) that there will be a more critical eye on all information from the surveyor moving forward.
-
Machine Control, which has taken over so much of grading work, relies on RTK and its inherent precision or lack thereof. The earthmoving industry has enthusiastically accepted it as the defacto standard. So I cannot criticize a surveyor who uses RTK to do common grading work simply for using RTK to do common grading work.
I have done surveying for earthwork on airports to FAA standards, which are very stringent. The various strata of lower level of subgrade where placed and graded using machine control and checked with RTK (GPS only at the time, but the sky was wide open). The uppermost strata, prior to the final lift of concrete, where checked with digital levels (on a grid laid out using RTK). The earthmovers would over-fill slightly and compact to finished grade because they were not allowed to skim off less than a couple of tenths, even if they could.
This the thing – it may be possible to run a grader blade at a certain height to a high precision if certain procedures are followed. But as soon as the material is walked on it will depress and have a different elevation in the footprints. If I’m wrong I’ll just bring on a bigger, heavier foot. The material is just not amenable to being graded to a higher degree of precision than RTK can measure unless very uncommonly specific – and time consuming – procedures are followed.
-
would also be interesting to know the firmware version you were using.
It’s Captivate v6.50.
-
I will continue to mark my stakes to the hundredth. It only takes a couple of seconds to write one more number on the stake. The combination of RTK vertical error and rounding could be a tenth. That’s not acceptable for me. Ideally the dirt crew will leave the grade a little high. There is a reason it’s called cutting grade. Pick up the windrow with a Paddle Pan and keep on moving.
-
would also be interesting to know the firmware version you were using.
It’s Captivate v6.50.
Wouldn’t it be the firmware in the receiver’s that matters more as that where processing it happening?
Also surprised those elevations are as good as they are, I had read them as metric (up to 70mm out) which given the size of the trees seemed likely.
-
Machine Control, which has taken over so much of grading work, relies on RTK
You can do machine control with conventional instruments too…
-
You can do machine control with conventional instruments too…
True. Quite possible, but not common.
-
@norman-oklahoma
Been watching it happen locally. Curb and gutter controlled by a robot, no stakes. Entire subdivisions built using machine control. One of the best things ever. Construction surveying will soon be a thing of the past.
-
@norman-oklahoma
Been watching it happen locally. Curb and gutter controlled by a robot, no stakes. Entire subdivisions built using machine control. One of the best things ever. Construction surveying will soon be a thing of the past.
You’re not far from it. Some things will stick around. I used to set up floor control in buildings so M.E.P.F’s and carpenters could lay out their stuff. Now we set up control so we can let Dusty the Robot lay out everything. The sub’s now send us their points and Dusty does it all at the same time. The future development plans for this dude are pretty wild!
-
Construction surveying will soon be a thing of the past.
Construction surveying as we have known it will soon be a thing of the past. Nowadays they need modellers and controllers. Hub pounders, not so much.
-
The logical choice for who provides the model is the firm that designed the project. No need to reinvent the wheel. Only QC and tweak it. On large public work projects most contractors employ people capable of doing the modeling.
-
Only QC and tweak it
The QC is absolutely vital.
We have all seen bad engineer’s plans – yes?
Well that BIM datafile is just the same
Only worse
!
Providing that QC “yes it can be built” at an early stage adds value – and contractors will pay $$$ – there’s a job there for surveyors.
Tweaking it adds much liability. But there is a often a need to take the engineer’s design and make it 3d and well modelled. Very good $$$ in that income stream too.
Then it gets set out – more surveyor $$$
And someone does AsBuilt and recording – probably a surveyor
And all of that is based around that one model and data source
That data has to be ‘right’
And it often isnt
And it often changes during the actual construction
If you are going to jump into that stream how do you properly QC a model at least as far as to your own satisfaction?
And what about to the satisfaction of your insurance company.
Got a good audit trail? and can you prove it when the proverbial hits the fan?
‘Cos it will…
-
@norman-oklahoma Common practice down here, especially getting toward finished grade. Makes sense to me, it is more precise. Sometimes you see both in use on the same site.
-
@norman-oklahoma – thanks for posting this and which constellations you were tracking – really interesting to see this data. I’ve been wondering how tight the vertical might be lately via a base/rover rtk setup
-
The logical choice for who provides the model is the firm that designed the project. No need to reinvent the wheel. Only QC and tweak it. On large public work projects most contractors employ people capable of doing the modeling.
Trust me I’d love to agree with you here, but most civil engineers & their CAD designers these days don’t have a clue about how to grade a project. The majority of them are only concerned with getting plans permitted and moving on to the next project – which I can understand is important but the quality of the designs or the ability to actually construct what they show leaves a lot to be desired. Some will send you a half way useable CAD file for GNSS models for construction and you can just check it before creating something from it. Others will either refuse to share a file, or they might send you a surface that has serious issues once you start evaluating the TIN. -OR- they send you something as laughable as “proposed contours” that are splines for sites that are dead flat (talking 0.5% or sometimes flatter around here) so you’re asking yourself “the plans don’t show any spot elevations nor slopes stated so what are we really doing from this contour to the next?” Assumption is dead flat but I’ve seen a lot of times where the engineers claim they wanted the parking lot inverted to convey the water thru the aisle to the inlet, yet the contour may not have depicted that due to the lack of elevation change? It’s maddening!
From what I’ve found too, most GNSS machine control systems require that particular brand’s proprietary file format and software to create the GNSS machine control files for the system. But those brand of machine control often can’t just import the engineer’s CAD file data directly from Autodesk C3D/LandDesktop, Carlson, Microstation or TBC – contrary to popular belief. You typically have to either have purchased the hardware from that brand for their software or add-in file conversion (via a serial number) or you can purchase the software they sell. Topcon/Sokkia & Trimble both seem to do this from what I can tell so I try to stick to building only Topcon machine control models via Civil 3D. I’ll start with a surface created in C3D, extract what I need out of it, export those items individually to the Topcon file types necessary (sometimes TIN is separate from linework if the contractor is running old stuff). Help the contractor with the control file & localization as that’s what Topcon’s procedures require, and then we’ll usually check the model to make sure the proposed grading makes sense with the cut & fills as well as where it’s saying to do so. How they mount the base is critical too – some will do some jank stuff with a wooden 8′ long 2×4 with a metal bracket & 5/8-11 stud welded to it and say “oh it’s fine – it didn’t move” LOL
-
I’m not suggesting that is what should be loaded into the machine. Only that the designer should provide their surface file. I don’t know any surveyor who is in the habit of obtaining information from others without checking, verifying and in this case modifying it for it’s intended use. There are places on almost every site that the operator needs to turn it off and freehand it. Landscape mounds with tight radius’s are an example of one. I haven’t seen many skidsteers or mini excavators with machine control.
-
I’ve seen far too many electronic files that were an absolute trainwreck, but somehow the paper output was acceptable and buildable.
If you can’t build it from a set of decent plans, who’s fault is that?
Tools, technology, and toys are great, and yes, the future is looming.
At what point did 3rd party folks become “entitled” to a model, tin, linework, etc?
The “staking role” was just transferred from one group of people to another.
And the initial folks were probably best situated to handle it anyway, and best capable of mitigating the risk/liability.
I don’t think too many give $0.02 of worry about how hard the model prep people have it.
-
At what point did 3rd party folks become “entitled” to a model, tin, linework, etc?
Never. But the owner/developer is entitled to the most efficient processes that lead to the completion of the desired development. When the engineer knows that a useable terrain model is a desired (ie/required to meet client expectations) deliverable, a useable terrain model will be delivered, or the engineering firm gets no more assignments.
It’s not just the staking and the earthworks. Look into the acronym “BIM”. There are loads of opportunities in the construction business for surveyors, but the role is changing.
-
Look into the acronym “BIM”.
BIM was those trainwrecks I was talking about earlier, which was at my last corporate job.
Automation and electronic deliverables is a wonderful thing, and we live in a wonderful time.
My experience has been that most places just don’t take the time to set everything up correctly, and don’t get people the appropriate training.
You’d think with the $100’s of thousands spent on Autodesk licensing, the achitects, engineers, and surveyors in a modern shop would integrate their packages so the workflow was how Autodesk intended.
Nope. Cut off their nose to spite their face.
Kinda odd how the last people in line (architects) are dictating how things start (surveying) and how the middle (engineering) must be changed to refelect “their vision”.
If anybody thought engineers were wishy-washy, you’re probably not going to like architects and BIM.
Besides, the carpenters layout most of the building stuff anyway. At least around here.
Log in to reply.