Activity Feed › Discussion Forums › Strictly Surveying › I could see the fumes
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> But this really misses the issue here. Which is one of a “surveyor” comparing a NAD83(2011) OPUS to a “modified state plane” based on an extensive NAD83(93) local network and declaring the network unusable on that evidence alone.
Actually, the original post didn’t specify how many OPUS solutions had been obtained on network points. The OP was ambiguous and MM jumped in with the blanket statement that he couldn’t possibly imagine how NAD83(2011)Epoch 2010.0 could be useful in checking the network, which was obviously wrong and worth discussing.
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> > Are you thinking that the actual construction plans don’t have bastardized coordinates on them?
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> So what if they do, Kent?Well, the most obvious method is to lay the project out in the plan coordinates if there are lots of coordinated points and you want to minimize your liability. So, the question is how to (a) check the control network that represents the means by which bastardized coordinates are to be determined on the ground and (b) how to simplify the use of GPS as much as possible (which means using a geoid model and not relying upon RTK “calibration” using control points along a corridor).
To me, the obvious implication is you actually check the control network to discover (a) how orthometric heights modeled from surveyed ellipsoid heights compare with the declared leveled heights of project control, (b) how the bastardized coordinate system is really related to NAD83(2011)Epoch 2010.0, and (c) specifically whether there is a significant rotation off grid North of the bastardized system and a significant scale error.
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> Actually, the original post didn’t specify how many OPUS solutions had been obtained on network points. The OP was ambiguous …
I suppose that we have all inserted our own assumptions based on our own experiences. But if I had a nickel for everytime some contractor’s staker has claimed a problem with my control, only to have that staker slink away quietly when presented with a detailed control report, to find his own error, well, I’d have almost a dollar now. -
You’ve gone past left field and are now in the parking lot.
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> > I do like LDPs but if a surveyor can’t survey in this simple surface coordinate system how in the heck will he figure out an LDP?
> If a surveyor can figure out the difference between Oklahoma South and Oklahoma North, it should be a short step to selecting Oklahoma South Central or Oklahoma Northwest or Oklahoma Panhandle.
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> It would just be 10 items in a list to choose from rather than 2. So, once codified and incorporated in the software, it’s easier, not harder, than modified state plane stuff. Particularly if using GPS. And if not using GPS the user can just ignore projections altogether.And if not using GPS the user can just ignore projections altogether
I don’t agree with that statement.
Now, I’ll stipulate that that statement might be valid on “small projects” in relatively flat terrain, but I have worked on very few of those in the last 45+ years.
I started using [essentially] LDP technology back in the mid-late 1970s, LONG before anybody was using GPS!
Ignoring the effect of “elevation” (vertical coefficient) when traversing or doing trilateration using “conventional” equipment, is the kiss of death in my neck of the woods (or desert).
Just saying…
Loyal -
> You’ve gone past left field and are now in the parking lot.
Yes, I understood that you didn’t think anyone should be checking the control network before construction staking. It didn’t particularly make any sense, though. Those of us in the private sector see liability issues a bit differently, I’m sure.
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After reading this entire thread, I have come to the conclusion that more than one of you will reject the project control that doesn’t match an OPUS solution, regardless of whether or not the project was actually based on an OPUS solution.
Anyone that doesn’t use the control provided in the plans should get the opportunity to stake a few bridge abutments in the wrong place. You’ll learn then.
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Early Adopter Here Too
Started using USC&GS control to close our route surveys on in the Colorado Mountains in the mid 70s. Got my hands on a paper by Mr Joseph Dracup that explained it all. Using his methods we changed the state plane coordinates of the control points to ground level values. Back then we didn’t call them bastardized I believe they were referred to as modified as I recall. Anyway I think Mr Dracup pretty much knew what he was talking about. We used to get some nice closures using T-2s and topmount EDMs.
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:good:
If one is concerned with “liability issues” as implied above, record your opus results, write down how you resolved the issue, and what coordinates you used for staking the project and why. But absolutely definitely, do not stray from the published coordinates from which the whole project was based. that will result in more liability than anything else.
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It’s something that really shows up surveying up and then back down a mountain. With your EDM shoot the distance up, then shoot the distance back down, reduce the distances to horizontal and compare. It opened my eyes for sure……
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> I don’t agree with that statement…..
That’s not exactly how I meant it. If control was properly established using an LDP, at a density appropriate to the needs of the project, and such control was used for stakeout control, the staker could treat the control coordinates as local control – no projection needed – for almost any ordinary use.I agree that there are circumstances where this statement would not be true.
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Norman
> > That’s not exactly how I meant it.
I suspected as much.
I only wished to clarify what I figured was obvious (to you and me anyway).
Loyal
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So you’re saying it’s more important for the bridge to match the centerline, storm sewer, sanitary sewer, right-of-way, sidewalks, inlet boxes, and utilities that are based on the control than it is to place the bridge at the precise geodetic coordinates shown on the plans? Or have I read you wrong?
[sarcasm]If this is what you mean, I am shocked, just shocked. [/sarcasm]
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Control Witching…
I’m beginning to understand now. OPUS, producing NAD83_2011 coordinates, is a witching stick for control network quality. Wave an OPUS solution over a printout of the published control. If the OPUS report extends straight, then you can rest assured that the control is fine. If the OPUS report “wilts” over the control printout, sorry pal, you’ve got some issues only Star*Net can resolve.
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We just watched that very thing happen. A two foot bust on a bridge build. Had to redo one of the abutments, not sure if it was a control issue but……..at least it was just a small foot bridge
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Control Witching…
> I’m beginning to understand now. OPUS, producing NAD83_2011 coordinates, is a witching stick for control network quality.
Actually, the simple question is how you go about checking anything with GPS methods if you don’t have a latitude and longitude and ellipsoid height of known accuracy. Considering how simple it is to get an accurate latitude, longitude, and ellipsoid height via OPUS, why would any surveyor want not to?
I realize that there are some folks who are worried that there is no way some bastardized control network can be checked by some method that derives accurate NAD83(2011)Epoch 2010.0 coordinates, but that’s obviously wrong.
If one wants to assume that the control network he’s “checking” is correct in its critical elements, should we also assume that he’ll adjust his EDM to exactly match the supposed plan distance between all control in order to check them without actually checking them?
In professional practice, checking means really checking, not wishing.
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On a bridge, like on staking a house, it doesn’t ever matter (usually) if the structure is within 0.2′ globally, but it has to be “gnat’s a$$” in relation to all of the other parts or components of the bridge. A surveyor needs to know when to be precise to a local control and when to be precise in relation to a global control.
You don’t want a building side to be off by 0.2 feet in its length, and you want the building to be square unto itself, but who cares if it’s to the 1/100,000 of a second lat or long. in its global location. Just so its oriented right and on its own property. Everyone understands this I think. We always used to measure the diagonals on a house stakeout before setting all of the offsets. (I only say “used to” because I don’t do that kind of work any more).
What amazes me is how big this thread is. I am thinking that everyone who posted on this thread gets it. It just seems like a clever thing to argue about.
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> After reading this entire thread, I have come to the conclusion that more than one of you will reject the project control that doesn’t match an OPUS solution, regardless of whether or not the project was actually based on an OPUS solution.
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> Anyone that doesn’t use the control provided in the plans should get the opportunity to stake a few bridge abutments in the wrong place. You’ll learn then.So, if a surveyor doesn’t check the control from which bridge abutments are laid out, should he notify his E&O carrier the day before work commences or wait until the claim is made?
And if he or she actually decides that it would be prudent to check the control points, should he or she (a) put a check mark in white crayon on them and take a photo to prove later than the were checked or (b) actually make accurate measurements to determine that the positions of the control points are substantially as claimed? Oh the better option is (b)? Well, if GPS is to be used to check the control, should a surveyor use wing-ding methods to measure it or should the surveyor use methods of known accuracy sufficient to the task?
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