> > 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.
>
> 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?
Stop being an ass, no one here is saying to not check the control. What we're saying is don't check it against something that had JACK SQUAT to do with it's establishment.
Your argument is akin to someone insisting that if a VW Beetle overheats, the first thing you should do is check the radiator.
😉 😉 😉 :good:
Your argument is akin to someone insisting that if a VW Beetle overheats, the first thing you should do is check the radiator.
LOL!!
> Stop being an ass, no one here is saying to not check the control. What we're saying is don't check it against something that had JACK SQUAT to do with it's establishment.
>
> Your argument is akin to someone insisting that if a VW Beetle overheats, the first thing you should do is check the radiator.
I disagree with the analogy. His argument is akin to getting a '69 bug and tearing it apart to see if it was built the specs of a 2013 beetle. And all of this before trying out the car and finding out if it runs (or overheats) at all. 😀
When I said....
You'll have to figure out a way to use it, it goes without saying that that would be in conjunction with the project owner, which around here means you figure out the best way to use it and get them to agree to it.
C'mon Karoly
That response was neither arrogant nor argumentative.
You may be posting to the wrong thread;-)
Don
Welcome to the Thread
> So, if you choose three points across a project, get decent OPUS-derived coordinates on each and the directions and distances between them (if for some reason you don't want to just transform one set of coordinates into the other system for comparison) show errors that are larger than acceptable (after allowing for the recipe that produced the bastardized project coordinates), then the Early Warning System is probably warranted. The odds are certainly in favor of a systemic problem.
Gee, Kent, if you're suggesting that you could consider the relative inverses between OPUS solutions with the relative inverses of the published control, you won't find any argument from me, except that this is probably not the most efficient means available to most GPS surveyors to accomplish the task. But it is entirely possible. How long will one have to occupy those three points for reliable OPUS results vs RTK or in-house post-processing?
Regardless, you've circled right back to where we all were when this thread started. Check the relative accuracies of the control you'll be using, but don't expect absolute agreement between HARN derived geodetic positions and OPUS derived geodetic positions. It won't happen. And in the example given, doesn't need to happen. Welcome to the party.
Welcome to the Thread
Whew!!! That's what is known as "taking the long way around the barn"!
Welcome to the Thread
Shawn, the point is and I can't stress this enough, DOT wants you to sit on the control as it's given to you and use it. Not introduce another system into it (they have seen this happen before), they not only don't want that, they insist you don't do it. I really don't think he has the equipment to accomplish this job, I'm pretty sure he doesn't have RTK so he can't do it anyway, he won't be hired to work on it which is a good thing, the idea of playing with a new EPOCH of NAD83 and shoving it to an older version, I've seen it before and it never ends well. He only probably can use OPUS, no doubt he doesn't have the capability of static processing and this is a sad desperate idea of how to do something he can't do correctly.
It doesn't really matter until someone with this mindset messes up good control with bad data. It has happened to me before, a number of times, so I'm pretty zoned in on it. It's something to watch out for and nip in the bud when you find someone doing it. They need to be stopped in their tracks and be forced to do control correctly.
you should add "and declaring it unuseable because it's NOT a 2013 beattle". 😐
Welcome to the Thread
> Gee, Kent, if you're suggesting that you could consider the relative inverses between OPUS solutions with the relative inverses of the published control, you won't find any argument from me, except that this is probably not the most efficient means available to most GPS surveyors to accomplish the task.
No, comparision of the residuals from a transformation would be much more direct and useful since that's the entire point of checking the control, to see how consistent it is and what systematic biases in orientation or scale it contains.
The point of mentioning OPUS was that various posters flatly denied that OPUS could be used to check a bastardized coordinate system. That was obvious not true and remains untrue. I'm glad you see the light.
> Stop being an ass, no one here is saying to not check the control. What we're saying is don't check it against something that had JACK SQUAT to do with it's establishment.
Well one of the fundamental principles of independent checking is that you try not to duplicate sources of systematic errors in what you're supposedly checking. For example, if a control network were surveyed conventionally, by your logic you'd have to borrow the exact instruments that were used to survey it when that obviously would be no check at all.
Welcome to the Thread
>...the idea of playing with a new EPOCH of NAD83 and shoving it to an older version, I've seen it before and it never ends well...
I'm not suggesting use of a new Epoch. Inverse those OPUS positions and inverse those HARN positions and you'll likely get great agreement in the inverses (with several caveats). The inverses are free from the adjustment offsets (NAD83_1993 to NAD83_2011). It's not a lot different than RTK or post-processing except less efficient (probably need to occupy each point for at least a couple of hours or more) and more prone to error (since the vectors are not directly observed between stations using OPUS). I'm not advocating this, but I can see it working.
The user would have to understand the likely positional errors output by OPUS in that area for the given amount of time of the sessions - ie 1 cm horizontally with 4 hour observations in that particular location (since the CORS geometry changes and not all sites are equal). Then he'd need to understand the effect these likely errors would have on the inverses. Like I said, not at all the most efficient or precise way of doing it, but if it works in Austin, who am I to judge?
> I disagree with the analogy. His argument is akin to getting a '69 bug and tearing it apart to see if it was built the specs of a 2013 beetle.
No, my argument is that if you want to work on a 1969 VW, you don't have to use gauges that were made in 1969 and you don't have to be standing in Wolfsburg, Germany.
The folks who are having a seizure over using OPUS-derived ellipsoid heights and latitudes and longitudes to check the geometric integrity of the declared control network are really objecting to making an accurate measurement of the network geometry to determine (a) its orientation bias, if any, (b) its scale errors, if any, and (c) where distortions appear in the network, i.e. whether they are just randomly sprinkled though the work or localized in certain areas.
Welcome to the Thread
> ...OPUS could be used to check a bastardized coordinate system
I'm not so sure it's a good idea for you to self study for your CEU's. Reading comprehension is clearly not one of your strengths.
Welcome to the Thread
thanks for the classic! :good:
Welcome to the Thread
Oh I understand the idea. However, it's beyond pointless, because you still didn't accomplish anything and the ellipsoid heights and lat, longs are going to be different when you already know what heights and lat, longs you need to hold. You don't go to the field and assign 4728.62 to your bench mark that has a published elevation of 4728.26, and say this is a better check because I will subtract 0.36 feet from each of my shots and see how they compare. No one would do such a thing and that is exactly what he is proposing to do. Bad practice. TERRIBLE IDEA And just the kind of thing I'm seeing surveyors do. Those numbers will get mixed up no question, and that's why it's NOT ALLOWED by the DOT.
Imagine the surveying class: Class the design team assigned an elevation of 100' to the finished first floor of this building and we leveled around it and came up with 0.01' difference on the two door openings, so for better control we are going to assign 100.54' to the finished floor and each time you level in an elevation you need to subtract 0.54' from your elevation to get the "correct" number.
At the risk of making this post so long it blows up Internet
here's what MM said in the op.
This guy went out and declared all the control unusable, the control we just got done checking which was all good.
So I ask what's wrong with the control?
Nothing, he says, this guy went out and started to run static OPUS on it and it didn't match.
Yes, I say; we know it doesn't match OPUS-so what.
This guy says we need to make it match
So the guy goes out and sets on a few control points, sends his data to OPUS, and when the OPUS coordinates on those points do not match plan coordinates, he says the control is "unusable" and it needs to be changed so it will "match". Agree or disagree with him?
To me this whole conversation reminds me of the lessons taught about the difference between "Accuracy" and "Precision". Are the project coordinates accurate? (correct vs. incorrect)? No, they are not. They don't match OPUS which we all presume, and have come to rely on, as producing "Accurate" lat/long/ellipsoid data (when properly used). Is the project control precise (well measured and fits with itself)? Yes, apparently, according to MM. This would be the role of the contracted surveyor, to verify "precision"...not accuracy, as he was provided a set of control values, presumably established by a competent surveyor. Upload the data from the spreadsheets into your data collector, pick a central or well broadcasting control point to occupy, select that point form the data list and start your base, check control throughout the project. Who cares about "Accurate" (correct lat/long)? In the reverse, if you spend a week setting 4 corners on a lot in a subdivision, pulling diagonals, verifying GPS measurements with a total station, verifying correct measurements to adjoining caps for two lots in each direction, and even staking the 4 lines with lath and flagging every 5' so the builder can see where the property lines are without mistake, thereby performing your work very precisely,.....it doesn't really matter when the owner calls you in two days when they show up to start the dirtwork and says that you surveyed the wrong address, that his lot is the one two lots down. (Inaccurate)
Just my two cents worth (and probably worth about $0.02 too)
> > Stop being an ass, no one here is saying to not check the control. What we're saying is don't check it against something that had JACK SQUAT to do with it's establishment.
>
> Well one of the fundamental principles of independent checking is that you try not to duplicate sources of systematic errors in what you're supposedly checking. For example, if a control network were surveyed conventionally, by your logic you'd have to borrow the exact instruments that were used to survey it when that obviously would be no check at all.
Except by using OPUS, you are introducing a "systematic error" into the system.
Did you ever perform any construction layout prior to the advent of survey grade GPS?
