GNSS Baseline Boundary Surveying
The PLS who sat in the chair before me, allowed the field crew I inherited to set a pair of 18? #5 rebar control points (CPs) with multiple GNSS occupations (NC’s Network-RTK) separated in time appropriately. Field crew was then allowed to setup their S7 robotic total station on one CP, backsight the other, then proceed to locate boundary corners, buildings, valves, or anything else. Often times, the field crew was able to get everything needed from just this one setup getting high-fives from my predecessor. They did not set additional stations and close. They did not, and were not required to, setup on the second control point and tie to something located from the first. Other than a direct and reverse shot from one CP to the other, no redundancy.
North Carolina, like many states, has tiered accuracy requirements for Urban 1:10K, Suburban 1-7.5K, and Farm 1:5K. The requirement for an Urban survey, in its entirety, reads as follows:
Urban Land Surveys (Class A). Urban surveys include lands that normally lie within a town or city. For Class A boundary surveys in North Carolina, the angular error of closure shall not exceed 20 seconds times the square root of the number of angles turned. The ratio of precision shall not exceed an error of closure of one foot per 10,000 feet of perimeter of the parcel of land (1:10,000). When using positional accuracy standards for Class A control and boundary surveys, neither axis of the 95 percent confidence level error ellipse for any control point or property corner shall exceed 0.10 feet or 0.030 meters plus 50 ppm measured relative to the position(s) of the horizontal control points or property corners used and referenced on the survey.
My view is that my predecessor met the standards on the control pairs but not any boundary corners located using his method. I’m now stuck trying to explain to the field crew how he’s wrong and I’m right. Not an easy task as my predecessor was president of a local survey chapter and was quite proud of his procedure. I’m essentially asking the crew to setup and close in a day-and-age when field crews almost never have a misclosure. Instead of being proud of tight closure, they view it as a waste of time, “Oh, what a surprise, EOC=0.008”. I don’t blame them for their attitude but I do want to improve it.
I’m not a fan of telling adults to do something just because I say to do it, although this is essentially what I did when I told them that there is no scenario involving a total station where we don’t close out the traverse (excepting route surveys with multiple GNSS pairs begging middle and end. I’m new to Carlson SurvNet, but I thought of showing them that even though the two CPs met NC’s 2 sigma accuracy standards, the boundary monuments did not. I’m trying to imagine how I would input it into Star*Net and I’m not sure that there’s sufficient redundancy to run it.
Am I wrong to view this as unacceptable for boundary or engineering topo?
Any ideas for a simple approach to help them understand the positional uncertainty resulting from this method?
Thank you
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