Wayne,
There are opinions, then there are un-called for, un-professional attacks. The gentleman came to the table being forthright and honest. I suspect he did so because that's the kind of person he is. His response to you puts him several notches up on some of the regulars around here.
The question he had directly related to those adjustments you derided in your response. Perhaps if you understood that Least Squares is more about quantifying precision than getting closer to perfect or true it would be productive to explain.
I would think being an LS from AZ you would also know that the system of surveying in your State is not based on the assumption of a flat earth. Again, not likely productive to expound.
Like you said, when you put comments on this board be ready to hear things you don't like.
My .02, Tom
Ok bionic, I'll bite on this one time.
How many lurkers are there out there that learn lots? I'd say lots. Good for them.
How many first time posters are there that seem to be fishing? I'd say lots. Ok, but expect some feedback you may not like. Case in point.
In my opinion, Mr Brain is fishing. He could be you for all I know?? IMVHO they (beerleg) should require a valid name for posting, not some made up pseudo persona to hide behind. I'm not defending the guy, nor am I attempting to disable his efforts. (opps, I used him and did not include him/her, so sorry ma'am/sir - assumption is that person is male)
That's all. I do think that the adjustment crowd has their respective heads in the sand as to how to do things. Again, my opinion. People can fudge numbers all day long, but it does not change one single fact. It is where it is. It is a simple yes or no question.
I also do think that acknowledging the difference between accuracy and precision is critical to any up and comer newbie wannabe's learning curve. Mr/Ms Brain seems more focused on precision than being right. IMVHO and $0.02
> How many lurkers are there out there that learn lots? I'd say lots. Good for them.
>
> How many first time posters are there that seem to be fishing? I'd say lots.
Exactly how is this a bad thing? Why does this forum exist if not to provide information? Who am I hurting by visiting this site and learning something to improve both myself and my work - which helps every other surveyor???
Forums are networking by like-minded individuals - without the need for travel.
>Ok, but expect some feedback you may not like. Case in point. In my opinion, Mr Brain is fishing. He could be you for all I know?? IMVHO they (beerleg) should require a valid name for posting, not some made up pseudo persona to hide behind.
ScatterBrain is a nickname that I have had for years. My name is Kevin Collins and I am male. I live and work in Kentucky. Is that enough for you Wayne?
> That's all. I do think that the adjustment crowd has their respective heads in the sand as to how to do things. Again, my opinion. People can fudge numbers all day long, but it does not change one single fact. It is where it is. It is a simple yes or no question.
Then answer me how you stake out a ' call - dead nuts on, no adjustments, no second tries, no fudging? Since I'm fishing, I might as well land the mother of all fish, right?
> I also do think that acknowledging the difference between accuracy and precision is critical to any up and comer newbie wannabe's learning curve. Mr/Ms Brain seems more focused on precision than being right. IMVHO and $0.02
Let me put it blunty, one last time. I'm not trying to fudge, cheat or otherwise justify crappy work - the field work's not been done yet.
I'm trying to comply with Kentucky minumum standards which requires a statement of positional accuracy on the plat.
I don't know:
1). The proper field technique to collect the information that will ultimately be used to generate the positional accuracy needed to comply with that requirement.
2). Perform the the calculations to generate the positional accuracy needed to comply with that requirement.
I came here asking for information that could lead me to solve both. Most people were genuinely helpful. All that you, Mr Wayne, wanted to do was to accuse me of cheating, lying to my boss, and fishing for information. (Guilty of the latter, haul me away in chains because I clearly am not worthy to be in your presence.)
All of that being said, I wish to apologize for my tone and obvious frustration to everyone else. I would like to thank those that recommended "GPS for Land Surveyors", I ordered it this morning from Amazon.
I would especially like to thank lmbrls for pointing me to the Duncan Parnell website and training course. It is EXACTLY what I was looking for - I think. I'm waiting on the approval to purchase the course, but the description looks like it fits the bill.
As other have mentioned -
redundancy
least squares
relative error ellipse
comparison vector length w/ ppm and error ellipses of each point to other points in the survey
I noticed you are in Kentucky. Since you are using Trimble gear in Kentucky, shoot me an email and I will send you a name to contact for a surveyor who I would definitely contact if I were using Trimble gear. He may be at your local dealer of all things Trimble.
Thank you Kevin
I'm not really a bad guy. I admire your ambition and approach to find a learning curve that works. I'm not pointing out yourself, it's just that there have been many before you just fishing. Ok?
Me, I went to college in the mid 70's for my BS degree, majored in surveying (Mich Tech). It took me a few years to get my LS because I did too much construction staking and not enough boundary work. It all worked out by late 80's though.
Bounced around MI in various duties back then. No regrets, not much money, but lots of experience. Now that I'm knocking on 60 here in sunny AZ, it's frustrating to see wannabe's expect instant gratification for things that took me (and many others) years to achieve.
25 yrs in business will teach you more than you may ever learn working for big firms and doing all that fun work you want to do. Some people are not cut out for the mold of self employment, but at the end of the day I think most of us surveyors are so independent that we are almost invincible in our own eyes. Welcome to the land of being a Land Surveyor.
Best of luck Kevin, and thank you. (Oh yea, my SWMBO is from Kansas City, so I have to be a Chiefs fan. Now Royals too.... ewwwww)
Thank you Kevin
it's frustrating to see wannabe's expect instant gratification for things that took me (and many others) years to achieve
Very frustrating indeed.
Definitely fits daily occurrences and the cause of many bad anonymous surveys.
Thank you Kevin
> it's frustrating to see wannabe's expect instant gratification for things that took me (and many others) years to achieve.
>
Welcome to the land of being a Land Surveyor.
>
> Best of luck Kevin, and thank you.
DDSM
:beer:
(I'm attending OPUS Projects Manager Training this Sat.)
> > How many lurkers are there out there that learn lots? I'd say lots. Good for them.
> >
> > How many first time posters are there that seem to be fishing? I'd say lots.
> Exactly how is this a bad thing? Why does this forum exist if not to provide information? Who am I hurting by visiting this site and learning something to improve both myself and my work - which helps every other surveyor???
>
> Forums are networking by like-minded individuals - without the need for travel.
>
>
> >Ok, but expect some feedback you may not like. Case in point. In my opinion, Mr Brain is fishing. He could be you for all I know?? IMVHO they (beerleg) should require a valid name for posting, not some made up pseudo persona to hide behind.
>
> ScatterBrain is a nickname that I have had for years. My name is Kevin Collins and I am male. I live and work in Kentucky. Is that enough for you Wayne?
>
>
> > That's all. I do think that the adjustment crowd has their respective heads in the sand as to how to do things. Again, my opinion. People can fudge numbers all day long, but it does not change one single fact. It is where it is. It is a simple yes or no question.
>
> Then answer me how you stake out a ' call - dead nuts on, no adjustments, no second tries, no fudging? Since I'm fishing, I might as well land the mother of all fish, right?
>
> > I also do think that acknowledging the difference between accuracy and precision is critical to any up and comer newbie wannabe's learning curve. Mr/Ms Brain seems more focused on precision than being right. IMVHO and $0.02
>
> Let me put it blunty, one last time. I'm not trying to fudge, cheat or otherwise justify crappy work - the field work's not been done yet.
>
> I'm trying to comply with Kentucky minumum standards which requires a statement of positional accuracy on the plat.
>
> I don't know:
> 1). The proper field technique to collect the information that will ultimately be used to generate the positional accuracy needed to comply with that requirement.
> 2). Perform the the calculations to generate the positional accuracy needed to comply with that requirement.
>
> I came here asking for information that could lead me to solve both. Most people were genuinely helpful. All that you, Mr Wayne, wanted to do was to accuse me of cheating, lying to my boss, and fishing for information. (Guilty of the latter, haul me away in chains because I clearly am not worthy to be in your presence.)
>
> All of that being said, I wish to apologize for my tone and obvious frustration to everyone else. I would like to thank those that recommended "GPS for Land Surveyors", I ordered it this morning from Amazon.
>
> I would especially like to thank lmbrls for pointing me to the Duncan Parnell website and training course. It is EXACTLY what I was looking for - I think. I'm waiting on the approval to purchase the course, but the description looks like it fits the bill.
:good: :good:
> The most authoritated answer to your question is the "Federal Geographic Data Committee Part 3: National Standard for Spatial Data Accuracy". The Duncan Parnell web site has a short online course and a spreadsheet for computations using the above stated standards. I believe it was less than $50.
The way I understand it, that standard is for determining the accuracy of a map product (lidar, photogrammetry, field-run topo). Read the scope and applicability statements. That is how I use it, anyway. I have used it to determine the precision of points from multiple sets of coordinates (using the average as the "ground position of higher accuracy"), but I am not sure that is appropriate, and I am not sure how you would use it to determine relative precision between points. Maybe they explain that in the course.
Why would the RPA be computed any differently for boundary corners than any other application using independent redundant measurements? Now if the question is this being the correct procedure for the application he has in mind? That is a totally different question. He can compute the correct RPA of the points resetting the corners if they are in the correct location or if they are very far from the correct location. Just like having a closure of one in infinity would not assure that the survey is correct. Math is a tool to get the correct answer; it is not the answer itself. If the property evidence is not collected and evaluated correctly computing the RPA is a mute point. It is a shame that as the Survey Profession has evolved considerably with the ability to perform complex computations that I have notice fewer surveyors that understand using the property evidence found in the field to correctly resolve the correct locations of the corners. My hope is that he cares and is not just mindlessly resetting the corners by resectioning a few corners and "setting some irons" base on math. The fact that he is not content to simply accepting any answer is a good sign. I hope he is not relying too heavily on a mathematical solution.
> Why would the RPA be computed any differently for boundary corners than any other application using independent redundant measurements?
I am questioning if the formulas for computing map data accuracy as spelled out in the standard you cite could be used to compute the RPA of a survey at all unless you re-measure some of your points using a more accurate method than what was originally used. Still, i would want somebody with a higher degree in statistics to give me their opinion. Do they have a different standard for cadastral data?
Please let me know if you find something that better defines the RPA for boundary corners. Your questioning has forced me to re examine my understanding of the concept. So far, I hold to my original statements. I really think the more important question is how is he determining the location of the corners. The RPA for the survey could be less than 0.07' and the corners could still be in the wrong location.
Minimum standards relating to precision have value. Used alone however they simply help us place corners in exactly the wrong place...
I think the 2011 ALTA/ACSM accuracy standards spell it out very well (and re-iterates exactly your point about the accurately-measured point being the wrong point altogether):
"E. Measurement Standards - The following measurement standards address Relative Positional Precision for the monuments or witnesses marking the corners of the surveyed property.
i. “Relative Positional Precision” means the length of the semi-major axis, expressed in feet or meters, of the error ellipse representing the uncertainty due to random errors in measurements in the location of the monument, or witness, marking any corner of the surveyed property relative to the monument, or witness, marking any other corner of the surveyed property at the 95 percent confidence level (two standard deviations). Relative Positional Precision is estimated by the results of a correctly weighted least squares adjustment of the survey.
ii. Any boundary lines and corners established or retraced may have uncertainties in location resulting from (1) the availability, condition, history and integrity of reference or controlling monuments, (2) ambiguities in the record descriptions or plats of the surveyed property or its adjoiners, (3) occupation or possession lines as they may differ from the written title lines, and (4) Relative Positional Precision. Of these four sources of uncertainty, only Relative Positional Precision is controllable, although due to the inherent errors in any measurement, it cannot be eliminated. The magnitude of the first three uncertainties can be projected based on evidence; Relative Positional Precision is estimated using statistical means (see Section 3.E.i. above and Section 3.E.v. below).
iii. The first three of these sources of uncertainty must be weighed as part of the evidence in the determination of where, in the surveyor’s opinion, the boundary lines and corners of the surveyed property should be located (see Section 3.D. above). Relative Positional Precision is a measure of how precisely the surveyor is able to monument and report those positions; it is not a substitute for the application of proper boundary law principles. A boundary corner or line may have a small Relative Positional Precision because the survey measurements were precise, yet still be in the wrong position (i.e. inaccurate) if it was established or retraced using faulty or improper application of boundary law principles."
"v. The maximum allowable Relative Positional Precision for an ALTA/ACSM Land Title Survey is 2 cm (0.07 feet) plus 50 parts per million (based on the direct distance between the two corners being tested)."
The standard you cited earlier is for testing the accuracy of mapping products, based on re-measuring points from the dataset using more accurate methods than were used to produce the map. The formulas it gives don't give you a constant-plus-ppm result as required by the ALTA standards. Re-measuring a few of the lines of a survey using more accurate methods than used in the original survey may be a valid way of testing your RPA, but this standard does not address how to do that.
"Federal Geographic Data Committee FGDC-STD-007.3-1998
Geospatial Positioning Accuracy Standards
Part 3: National Standard for Spatial Data Accuracy
3-1
3.1 Introduction
3.1.1 Objective
The National Standard for Spatial Data Accuracy (NSSDA) implements a statistical and testing
methodology for estimating the positional accuracy of points on maps and in digital geospatial data,
with respect to georeferenced ground positions of higher accuracy."
"3.2 Testing Methodology And Reporting Requirements
3.2.1 Spatial Accuracy
The NSSDA uses root-mean-square error (RMSE) to estimate positional accuracy. RMSE is the
square root of the average of the set of squared differences between dataset coordinate values and
coordinate values from an independent source of higher accuracy for identical points.
Accuracy is reported in ground distances at the 95% confidence level. Accuracy reported at the 95%
confidence level means that 95% of the positions in the dataset will have an error with respect to true
ground position that is equal to or smaller than the reported accuracy value. The reported accuracy
value reflects all uncertainties, including those introduced by geodetic control coordinates,
compilation, and final computation of ground coordinate values in the product.
3.2.2 Accuracy Test Guidelines
According to the Spatial Data Transfer Standard (SDTS) (ANSI-NCITS, 1998), accuracy testing by
an independent source of higher accuracy is the preferred test for positional accuracy.
Consequently, the NSSDA presents guidelines for accuracy testing by an independent source of
higher accuracy. The independent source of higher accuracy shall the highest accuracy feasible and
practicable to evaluate the accuracy of the dataset.2
The data producer shall determine the geographic extent of testing. Horizontal accuracy shall be
tested by comparing the planimetric coordinates of well-defined points3 in the dataset with
coordinates of the same points from an independent source of higher accuracy. Vertical accuracy
shall be tested by comparing the elevations in the dataset with elevations of the same points as
determined from an independent source of higher accuracy.
Errors in recording or processing data, such as reversing signs or inconsistencies between the dataset
and independent source of higher accuracy in coordinate reference system definition, must be
corrected before computing the accuracy value.
A minimum of 20 check points shall be tested, distributed to reflect the geographic area of interest
and the distribution of error in the dataset.4 When 20 points are tested, the 95% confidence level
allows one point to fail the threshold given in product specifications."
Of course I could be comletely wrong, too. This is just my understanding of the matter.
