So a client hires me to for a survey to determine whether or not the new building that he just erected on an existing concrete slab:
1- Meets the county's 8' setback requirement.
2- Is actually on his irate neighbor's property. (who just reported him to county planning departed and started this whole saga)?ÿ
There is a hodge-podge of stuff in this this particular project file.?ÿ
-GNSS (VRS) of 3 of the 4 property corners.
-Rounds from a base line between 2 known points to the last property corner.?ÿ (From 2 separate base lines)
-Total Station Topo shots of all structures on the property.
The last corner was shot using the TS and Rounds because it was in a location that I could not get reliable GNSS signal (Trimble R8-2) and I could not set a tripod over (It is about 2 tenths off of a chain link fence line).?ÿ ?ÿI set up a prism pole on a bipod and shot rounds to it from two separate base lines.
I understand if I shot this in all GNSS I could compute the 95% confidence level needed for the State of NC.?ÿ And if I traversed the whole thing then I could compute the positional accuracy as a ratio.?ÿ ?ÿ ?ÿBut since this is "Frankensteined", I'm not sure how to compute this. (Can it be computed in Access 2015?)?ÿ ?ÿ ?ÿIdeas?
Thank you!
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IANAS?ÿ
IANAL
The idea of this is already under contention and in hot water, my lack of trust in warring parties and forthcoming information,
I'd set up and occupy Known accepted monuments from NCDOT NGS whatever, get real world coordinates and shoot the boundary to the tightest tolerance I could with the TS.
Tie out the block or anything else that's there for the win.
This screams lawyers making money to me, and they're looking for any available liability insurance to make sure they get paid.
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Like I mentioned earlier
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IANAS
yet.
If you had TBC and had rtk and total station data and had a good network of observations from the total station multiple baselines and rtk where it makes sense then you could easily perform a least squares adjustment with all the measuring tools you have and calculate the relative position error tolerance you are looking for . I imagine it really doesn??t matter if you are on some known datum but you need to meet state standards for either a traverse closure or a relative position error tolerance much like alta requires. Now that all has to do with measurements. ?ÿI would get that out of the way. But make sure your boundary resolution is what is correct. ?ÿThat probably has little to do with how well you measured. We can be precisely wrong. And from stating the pas is on neighbors property. Means someone assumed they were on their property. ?ÿWhy is the question I would be asking. I don??t think Trimble access can give you all what you want but I could be wrong as far as position error tolerance. I know you can change the confidence level from DRMS to 95% confidence in the settings. You could manually calc your total station values if you take the specs. And number of rounds etc. to solve for it. But very time consuming. Lol.?ÿ
You have any least squares software you can do this it doesn??t just have to be TBC. ?ÿCivil3d as bad as it is at least squares in my opinion you could solve. Starnet. Etc. ?ÿ
Presuming that the GNSS ties and the TS observations have some common points I don't see a problem here. If that is not the case more field work is needed.?ÿ
Crazy easy to compute positional tolerance for TS work, combined with GNSS or otherwise, using least squares. I'm a Star*Net guy, but if you own Carlson Survey you own a least squares adjustment program.?ÿ ?ÿThere are plenty of others.?ÿ If your state has these positional tolerance statutory requirements I think that you need to get up to speed on this thing. Or farm the work out.
@jitterboogie Why are real world coordinates relevant to a boundary survey in North Carolina? Wouldn't this just be extra work that is a waste of time and the client's money?
@lurker?ÿ
21 NCAC 56.1602 (g)
(g) Tie lines defined. Where the results of a survey are reported in the form of a plat or a written description, one or more corners shall, by a system of azimuths or courses and distances, be accurately tied to and coordinated with a horizontal control monument of some United States or State Agency survey system, such as the North Carolina Geodetic Survey,
North Carolina is anal retentive, in my opinion.?ÿ They are burdening their population with unnecessary expectations.?ÿ Some will say there is no additional cost to the client, but, that is because that is consistent with all of the work they do.?ÿ Others will say that adding the tie requirement dictates the survey provider to invest in equipment that is not required, otherwise, to provide the survey service perfectly well.
While NC is at it, perhaps they should dictate that elevations also be provided for every property corner.?ÿ That information is useless, in the general case, for a boundary survey, but easily provided when the tie requirement is in force.
North Carolina is anal retentive, in my opinion.?ÿ
That statute smells like an attempt by somebody to get NC surveyors to pay attention to raw data (coordinate lists are not raw data), to inspect and analyse it, to understand the concepts of positional tolerance, and to be able to perform adjustments when appropriate.?ÿ Apply pejoratives to that if you will, but it appears -to me- to be an attempt to address a perceived problem.?ÿ ?ÿ?ÿ
I understand if I shot this in all GNSS I could compute the 95% confidence level needed for the State of NC
At risk of asking a stupid question, by what procedure are you computing '95% confidence level' when doing a complete survey by GNSS VRS? Genuinely asking.
There are millions of lots in this country that can be surveyed quite adequately by use of a steel tape and proper procedures.
I understand if I shot this in all GNSS I could compute the 95% confidence level needed for the State of NC
At risk of asking a stupid question, by what procedure are you computing '95% confidence level' when doing a complete survey by GNSS VRS? Genuinely asking.
There was a training I attended from Duncan Parnell that went through the process.?ÿ A video still persists somewhere on their training site.?ÿ There were two methods to calculate.?ÿ One used the Geospatial Positioning Accuracy Standards
Part 3: National Standard for Spatial Data Accuracy document in conjunction with an excel spreadsheet to do the calcs.?ÿ ?ÿThe other used a trimble accuracy style sheet that would calc for you.?ÿ (I've done both but now use the style sheet for efficiency and ease of use)?ÿ
Observe the position (180 epochs) on at least 2 separate occasions that are at least 4 hours apart. (To ensure different satellite configurations)?ÿ ?ÿ
Make sure that the point is named the same and use the "store another" choice when offered.
Afterwards, use the accuracy style sheet and it will produce a report on whether it meets the 95% standard or if you need to re-observe.
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While some states may not explicitly spell out what "relative positional precision" means in their statutes, the current ALTA/NSPS Land Title Survey standards give a pretty good explanation:
??Relative Positional Precision? means the length of the semi-major axis, expressed in meters or feet, of the error ellipse representing the uncertainty in the position of the monument or witness marking any boundary corner of the surveyed property relative to the position of the monument or witness marking an immediately adjacent boundary corner of the surveyed property resulting from random errors in the measurements made in determining those positions at the 95 percent confidence level. Relative Positional Precision can be estimated by the results of a correctly weighted least squares adjustment of the survey. Alternatively, Relative Positional Precision can be estimated by the standard deviation of the distance between the monument or witness marking any boundary corner of the surveyed property and the monument or witness marking an immediately adjacent boundary corner of the surveyed property (called local accuracy) that can be computed using the full covariance matrix of the coordinate inverse between any given pair of points, understanding that Relative Positional Precision is based on the 95 percent confidence level, or approximately 2 standard deviations."
In other words, statistics matter and weighting of observations must be applied.
As others have mentioned, least squares analysis does not care whether the observations are GNSS or terrestrial. It can handle level data, or angles only, or distances only, etc. etc.
The Trimble report mentioned upthread is likely the "ALTA/NSPS Allowable Relative Tolerance Report" embedded in TBC, and it does require a network adjustment to be performed in order to run properly.
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The calculations themselves are simple if one does not have TBC. After the network adjustment is performed, compute
A: the square root of the sum of the squares of the semi-major axes of the error ellipses of the two endpoints in question, and?ÿ
B: multiply the allowable error PPM by the distance between the two points, then add it to the allowable error constant value
If A is less than B, it passes. If A is greater than B, it fails the test.
It might have something to do with the fact that NC conceived of the concept of SPCSs. Also, you don't have to do it if there's no NCGS monument within 2000' ft of the subject parcel and there's no requirement to use GNSS.
What I and others have found is that Grid ties save our clients money.?ÿ I charge more if I pull the deeds and don't find any Grid ties because I know it'll take a bit longer to find corners.?ÿ North Carolina provides one of the most robust and well maintained VRNs in the country for a one time license fee of $500. We have free statewide LiDAR data that is on it's fifth iteration and also gives us free ortho-imagery.?ÿ?ÿ
Although it's discussed often here, I think it's still easy for those in PLSSia to forget that we have no map showing the hypothetical cadastre and no corner records.?ÿ I've never heard of a NC PLS resetting a corner by the Grid tie, but it can be quite helpful when determining best available evidence.
Grid tie aside, NC is anal retentive about their survey certification language. It's the most convoluted mess I've ever seen and frankly embarrassing when compared to our neighbors.
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