Sigh!!! It's all i can say!
The whole gist of this thread is what Jimi Hendrix said in 67 "Man if I have to Xplain it to yah, You ain't never gonna understand" Get an education for the foundation. :-S
Pablo B-)
Pablo, I'm completely defeated, I've never been this confounded. But it does explain a lot of what I've run up against this last ten or so years. WOW!!!!!:-O
Apparently your guy is not the only one that would have gone off on that tangent. Control coordinates used for design and provided for construction have to be used, regardless of how "correct" they are. As long as they agree with each other, doesn't matter. Project owners control that, not the layout guy.
> What are you talking about? You arent making any sense! Shawn is completle on topic!
Well, if the topic is checking some control network of unknown quality provided by some third party, what doesn't make sense about what I posted? The correct reduction of GPS vectors depends upon accurate ellipsoid heights, so obviously you want to get an ellipsoid height of known accuracy from an independent source. OPUS would be my first choice. The only other options that come to mind would be (a) using an ellipsoid height from an autonomous position or (b) assuming that the ellipsoid height of one of the control points to be checked is ... correct. I don't consider either of those to be very good options, particularly considering how easy it is to get a very good ellipsoid height via OPUS.
To compute an accurate orientation of a GPS-derived network in some projection, you also need accurate latitudes and longitudes for your control points from which you extend your survey. Your options are (a) use a latitude and longitude from an autonomous position, (b) assume that the latitude and longitude of one of the control points to be checked is ... correct, or (c) actually get a very good latitude and longitude via OPUS.
So, what you end up with in your validation survey is a truly independent check upon the ellipsoid heights and horizontal positions of the control point that will be used in the rest of the surveying activities. Any of the other options aren't truly independent checks because assuming an erroneous value might introduce some systematic biases throughout the survey.
The simplest way to compare the validation survey coordinates to the "as-provided" coordinates is by 3D transformation. This way, you can see for real whether or not there are any problem areas in the control network and can devise a proper strategy to deal with them. It is entirely conceivable that just three OPUS-derived check coordinates across a control network would raise a red flag about the quality of the network. Not saying this is obviously the case here, but it isn't ridiculous as a possibility.
Holy cr@$!!!
Please tell me said plans have an urban section with 15 or 20 curb returns and that truly confounding statement for the button pushers: "Match Existing"
Ain't surveying cool.
Steve
Well said!!!!!!
Lol. No very rural. 10 miles, maybe 15 land owners. U.S. highway
The correct spelling is ©®Ãþ 😛
Apples and Pomegranates guys.
Translating 2 systems accurately is difficult, if not impossible, even with some sort of transformation protocol. Can't do a direct '27 datum to '83 datum transformation. At best its an approximation. But lets unruffle some feathers here and let this be a proper discussion. So far it is one of the best OPUS discussions which I was looking for in a recent post. So thanks for that.
You have a file projected to a surface coordinate system. A modified state plane if you will. The points are leveled to a first order bench system. What would be the proper procedure tocalculate an ellipsoid height for each point holding the fixed leveled elevation and applying a geoid model. Hint, hint it will not involve Opus and will take about a minute to do......
> You have a file projected to a surface coordinate system. A modified state plane if you will.
>The points are leveled to a first order bench system. What would be the proper procedure tocalculate an ellipsoid height for each point holding the fixed leveled elevation and applying a geoid model.
Were you thinking that GPS wouldn't be used in any of the project surveying in connection with construction? No machine control? Basically, if you're using GPS, you'll need a geoid model and that will probably involve carefully resurveying your control.
> But lets unruffle some feathers here and let this be a proper discussion. So far it is one of the best OPUS discussions which I was looking for in a recent post. So thanks for that.
Yes, the problem is interesting. Unless the control points are semi-jacked, it should be a simple matter to calculate the transformation that relates NAD(1993) to NAD(2011) within the project area. That is just a four parameter transformation. If the control points are semi-jacked or worse, there will be distortions in some areas that the plan of attack needs to take into account.
If the leveled values of control points don't have a constant difference from the orthometric heights derived from GPS with geoid model, the question is how to model the differences if you want to use GPS.
> > But lets unruffle some feathers here and let this be a proper discussion. So far it is one of the best OPUS discussions which I was looking for in a recent post. So thanks for that.
>
> Yes, the problem is interesting. Unless the control points are semi-jacked, it should be a simple matter to calculate the transformation that relates NAD(1993) to NAD(2011) within the project area. That is just a four parameter transformation. If the control points are semi-jacked or worse, there will be distortions in some areas that the plan of attack needs to take into account.
>
> If the leveled values of control points don't have a constant difference from the orthometric heights derived from GPS with geoid model, the question is how to model the differences if you want to use GPS.
I think what MM is saying is that the construction surveyor called the control "off" without doing the necessary transformations from 1993 to 2011. In other words the lats, lons, hts, N-E-Z, (based on 1993 data) of the provided control will not match new shiny 2011 OPUS derived lats, lons, hts, N-E-Z 2011 data without some form of transformation/calibraton.
> I think what MM is saying is that the construction surveyor called the control "off" without doing the necessary transformations from 1993 to 2011. In other words the lats, lons, hts, N-E-Z, (based on 1993 data) of the provided control will not match new shiny 2011 OPUS derived lats, lons, hts, N-E-Z 2011 data without some form of transformation/calibraton.
What MM posted above was that:
> After all that the construction is bid and they start the project, all the surveyor needs to do at that point is set on the control-yes typical DOT-NAD83 State Plane with a scale factor to bring it to surface-easy!
To me, that means that the project coordinate system is some bastardized "surface" coordinate system that actually does require determining what transformation relates it to the real world of NAD83 if you're planning on using GPS on the job in some way other than the typical RTK jockey calibration-du-jour method.
To me, that means that the project coordinate system is some bastardized "surface" coordinate system that actually does require determining what transformation relates it to the real world of NAD83 ......
Really? Gee, that was the whole point of the OP. It sounds like there have been many miles of highway built using the existing control system, why wouldn't it be suitable for the next few miles???
However, who knows, maybe the entire highway has been built in the wrong location and at the wrong elevations and now they need to move it a few tenths to match the new NAD 2011............... Maybe this is the new definition of "shovel ready jobs"
> To me, that means that the project coordinate system is some bastardized "surface" coordinate system that actually does require determining what transformation relates it to the real world of NAD83 ......
>
>
> Really?
Yeah, if you want to compute a transformation that fits the whole job as any professional surveyor would. I like to do things the easy way and the RTKlusterfugal method of calibrating on the nearest control points in some bastardized system ain't it.
phase line
Remarkable that the thread went on for so long before someone mentioned the most basic thing of all. Although I could have missed it.
All that fancy geodesy and corrections, adjustments, ellipsoids and legacy arguments are interesting but what is even more interesting is whether or not the physical match line fits. Gravity likes a slope when expected to convey sewer and people are pretty attached to straight lines and 90 degree angles.
I can't imagine I am alone in having seen a project with monumented control that fit itself but not the topography on which design was based.
Yes, the problem is interesting. Unless the control points are semi-jacked, it should be a simple matter to calculate the transformation that relates NAD(1993) to NAD(2011) within the project area. That is just a four parameter transformation. If the control points are semi-jacked or worse, there will be distortions in some areas that the plan of attack needs to take into account.
So in essence you are saying that you refuse to do the job you are contracted for which is to check the control using the values provided, you refuse to even occupy the passive network that is the basis of the control. You refuse to survey in NAD83/93 as stipulated in your contract. Is it too complicated for you? You don't understand how to survey to project control? Why can't you preform such a simple surveying task?
If the leveled values of control points don't have a constant difference from the orthometric heights derived from GPS with geoid model, the question is how to model the differences if you want to use GPS.
Really, you don't understand how to do that?
I'm not that smart, and I must be missing something here, but I really don't understand why this is so difficult to get.
If I am given a control file I check that control file against itself, then against all the proposed improvements. Why on earth would you pull in an outside source, which was never intended to be used, to say something is good or bad??!!
If I check a dozen or so points and they work within tolerance of what is given to me, and again work well within the confines of the network/job, I'm good to go.
