In anyones opinion, say hypotheticaly that you have a triangle control network, 3 points equal distance apart maybe 400', you have tight elevations on the three. Now take 4 different robotic instruments, 3 Trimble and 1 Leica and set at four random locations around the triangle and all of them resect off of the three points. What are the odds that they could all tie down the same random point in the middle of the triangle and come up with the same NEZ? What kind of descrepancies would you expect to see?
See, it all depends on the control. I love free-stationing, and I've had excellent results with it, but it's only as good as the stuff I come off of. GIGO.
Depending on "how tight", I might expect to come up with the same value within the third decimal place on the coordinate values and the second decimal place on the elevation. That would be flat to me anyway.
Sounds like a good experiment for a slow day. I've used both two and three point resections for years on stakeout work where the little bit of error I might pick up with the resection will not affect the results. I have always avoided them in situations where the horizontal or vertical tolerances are critical or when my area of interest extended beyond the area bounded by the control.
I would expect that any difference would be unnoticeable to me.
0.01 or less if the control is good and you turn sets through the resection.
I'm with Mr. Foggy
The powers that be tell us that over the entire project, that each 1/8" of concrete = $1M
The grading group, who is responsible for one of the Trimbles, cut, stabilize, then we have one of our guys asbuilt their grade. That is Trimble #2. A sub lays hotmix on that then we send a different guy (Trimble3) to asbuilt that and set paving nails. After that the paving group rolls in with their Leica Machine Control and pave.
Of the four, nobody wants to claim the extra 1/8".
In my example there is a good shot at having decent geometry, but in reality the control is every three hundred feet down the length and zig zagging on each side of the roadway.
> What kind of descrepancies would you expect to see?
I'd expect the "tightness" of the located point to be nearly equivalent to the "tightness" of the control.
Whether the instrument is a Trimble, Leica or whatever is immaterial at this conjuncture.
What the instrument is spec’d at is very material to the results. If the instrument is spec’d at 0^00’03” horz and 3mm +/-3ppm then you’ll get better results than one spec’d at 0^00’05” horz & 5mm +/-5ppm.
I’ve noticed that you’re using Trimble for “regular” layout and the Leica 1200’s for paving. What’s the Model # on the Leica’s? 1203 = +/-3”, 1201=+/-1”.
Next is the methodology; are you using a range pole with a piece lath for a brace or using Tripods with tribrachs & prisms? As mentioned above you’re only as good as the methods and instruments you use to establish your control points. Are you turning multiple angles and reading multiple distances with the temp, humidity & pressure taken under a shaded area?
Last but by no means least is the stability of your monuments… if they’re not to NGS spec’s then they’re going to move in the active soils we have around here. +/-0.01’ is a very tight tolerance and you need to use the proper instruments & procedures to achieve something anywhere that close.
If you need an independent outside party to verify these million dollar results I’m just 15 minutes from this project.
Again, your results will only be as good as what you are using as a reference.
It has been a great tool for setting up, shooting some obvious previously located objects and to start looking for my original control.
What is the tolerance for the job? The $1m could be + or -, I'd think it would average out.
I think that they are just trying to "tighten" everyone up. Heck, 1/8" is only 0.01'. I thought the DOT requirements around here of 1/4" was pushing it.
Maybe the 1/8" was in the other direction and they really saved $1M.
I don't do road work, but I find it difficult to believe that a concrete or asphalt laying machine can consistently meet a 1/8" tolerance horizontally or vertically no matter how it's controlled.
This is a losing battle because they (the paper pushers) are trying to hold you to math that only works on paper, as opposed to the physical placing of materials in the field.
You can fine grade all day long to try to avoid that mythical 1/8th inch, but it will be the people that run the batch plant that will have the most effect on the total yield.
Is there 10 cubic yards of concrete in that truck?
Sure there is...
The Trimbles are 1" instruments. I am not real sure about the Leicas but have sent an email to the guy that is responsible for it.
My whole stand on it is with four seperate pieces of equipment with four different operators ( two of which arent surveyors but a grade checker and a paving guy) in four very different resection locations that if we can all get within an 8th we are doing good.
I was going to suggest we set all four up and experiment to show them that we cant get closer.
We are batching our own.
And I agree, it is absurd, but everyone is pointing the finger at everyone else.
Instead of finger pointing, everyone should band together and give the powers that be a quick course in error theory and point out the absurdity of trying to build something like a road with a micrometer. Just because the "standard" can be written doesn't mean that it can be met!
In order to have a prayer of detecting at the 0.01' level you are going to have to use levelling to determine elevations - and preferably a digital level. We do airport runway work where the FAA mandates a vertical tolerance of +/- 0.04'. The contractors find that to be a challenge to meet. We layout points to be topo'd using GPS, then level each point. Stainless steel rods driven to refusal are used for elevation control.
Needless to say, production is measured on a different scale from that used for ordinary work.
> In order to have a prayer of detecting at the 0.01' level you are going to have to use levelling to determine elevations - and preferably a digital level. We do airport runway work where the FAA mandates a vertical tolerance of +/- 0.04'. The contractors find that to be a challenge to meet. We layout points to be topo'd using GPS, then level each point. Stainless steel rods driven to refusal are used for elevation control.
>
All, well mostly all, of our control is Bernstein Rods driven to refusal.We have put some nails and xcuts on some of the permanent work that we have already built.13"concrete on 4 inches of asphalt on 12" of flexbase on soil lime stabilized to 36" We have a dedicated control crew, all they do is burn and turn. We do a 3 minute static shot, turn the pole 180 and do another 3 minutes. We run digital level loops on everything. This is the tightest control I have ever worked with other than what I used at the Supercollider.
The finger should be pointed at the bean counters.
Somebody needs to sit those good old boys down and explain the difference between accuracy and precision.
If an eighth of an inch is a million, then that means a sixteenth is 500k, a thirty-second is 250k. I don't know about you, but $250,000 would surely help my current financial situation and all for the thickness of a fingernail?
Somebody needs to bring these folks back down to reality.
Doug