For Board requirements, how would resections play into meeting the "ratio of precision shall not exceed an error of closure of one foot per 10,000 feet" (for urban surveys)??ÿ
These linear closure based specifications are archaic. If your state laws continue to use them the law should be amended. But, in the mean time, it isn't always strictly necessary to actually show that every survey has a closure, only that your procedure would normally produce data of equal or better accuracy?ÿ ?ÿ
Hi Murphy, Im in NC as well.
We use SurvNet for Error Ellipses when needed, but at the end of the day if a crew is using 2 points they should backsite check out.?ÿ That creates redundancy and in my opinion could be used for providing closure as you have distance and error to compute.
If you really feel you need to adjust it then you SurvNet Least Squares.
Though I will say I always have new crews close triangles including closing angles when they first start.?ÿ Mainly so they understand the concept and procedure.?ÿ?ÿ
@rover83?ÿ
Yep!
We designed and created the Las Cruces LDP this way.
If we could utilize a gravity survey for true elevation that would have been the cherry on top!
@field-dog When you put coordinates on the two points you are describing their relationship to each other.
@wal1170 Of course you can. I could create repeatable points using a recreational hand held Garmin. I could create repeatable points using a rubber band to measure with. It is always about how much error will you allow in those repeatable points which is exactly what is being discussed.
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Even 0.10 might be difficult using RTK exclusively. If you have a reading of 0.03', that is only 65% from what I understand. If you went 95%, you would certainly have more than 0.1' of possible error between the two. Given that, the originally described method might be the ticket. They are taking multiple, time separated shots on the points. Shooting a common point with a total station is probably the only way to get the accuracy stated without a lot more work. The OP's insistence on shooting a common point from each station is the only way I know of to actually know what the accuracy expectation is. Without that, it is just a guess.
Yes, slightly off topic...I have often wondered if shall always means maybe now, or just for the ALTA/NSPS Standards.
@dmyhill?ÿ
multiple redundant measurements are the only way. And, of course it's important to realize setting a point isn't as accurate as locating one.?ÿ
Take a Leica GS18, the stated performance for RTK is 8mm plus 1 PPM. When it comes to redundant measurements, they would need to be spaced in time, and I will openly admit that I do not know how many and how long it would take to get a true random sample. I am 100% certain choosing 100 epochs doesnt cut it.
So, let's say we do a full blown 24 hour static session. Perhaps we get down to "perfect". At that point, you are also subject to whatever error there may be in the math (ellipsoid, etc) compared to true ground.
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I am not denigrating RTK, but I think some in the industry blithely consider 0.1' as easily obtainable for ABSOLUTE accuracy. With a total station, it is brain dead easy to get that precision, and therefore that accuracy relative to our control, but the geometry of GNSS is immutable.
Yeah. Had this conversation about a fellow professional around here. The board has dealt with him a few times, but the lawyers have their say and he still has his license.?ÿ
@rover83?ÿ
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Far more useful to quote the whole thing, because I think the WA statute works very well. While setting a standard, it also allows for a way for us not to be liars by stating the accuracy that we did achieve. Of course, none of this thread has to do with WA, the OP is in NC, I believe. Apparently, we have found something WA did better than NC.
(and thank you for letting me know that ALTA/NSPS doesn't stand for the AG's office)?ÿ
WAC 332-130-085
Relative accuracy standards for land boundary surveys.
@lurker?ÿ
So you answered your own question...you can create repeatable points.
It is always about how much error...and that part of the professional part of professional surveyor: knowing how much error is ok when and where.
Now tell me: What is the precision of the datum to the real world?
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Seriously. I remember a seminar by a very knowledgeable former NGS employee, where the speaker talked on and on about precision and accuracy and everyone was nodding their heads, then he asked them essentially that question. And then we discussed how none of us has any chance to know such a thing because it is hidden in the proprietary code.
@dmyhill that's a good question, I'll have to think about it.
That said, a friend of mine regularly runs various brands of RTK through a calibration baseline, including points with overstory. My understanding is that they generally are true to their specs.
My point is more about placing a question mark on the usefulness of demanding precision and accuracy, while we leave certain aspects out of the equation.
Asking for a friend.............................precisely how wide is a gnat's ass?
I thought you North Carolinians surveyed from a cucumber tree to the brow of a hill to the stone fence to the southwesterly corner of Murphy Brown's front porch back to the cucumber tree.
@dmyhill It wasn't my question. wal1170 asked "have you ever been able to create GNSS control point that is repeatable?"
@rover83?ÿ Agreed, I have secondary points that I have occupied repeated over a twenty-year period. They always produce the same values when the observation error is good.