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Checking the pulse of traverse closure
Posted by Stillplumb on March 1, 2024 at 2:44 pmJust looking for thoughts/replies about general practices on traverse closure and adjustment, along the lines of personal minimum standards vs. your state minimum standards.
For instance, your state minimum standard for unadjusted closure is 1:10,000. Do you have a higher personal unadjusted minimum that you require of your crews? Do you adjust every traverse?
What if the crews usually average 1:20,000-35,000 for general boundary work and they bring in a 1:10,500 traverse on a boundary survey. Do you accept it as is and move on, adjust it, or send them back out to check? Under what circumstances would you have them re-shoot the traverse? Accuracy is always good, and time is money.
Any other thoughts?
dwoolley replied 3 weeks, 2 days ago 18 Members · 29 Replies- 29 Replies
Back in the 90’s if we closed less than 1:50000 and or the angle angle misclosure was less than the old specs we re ran them. That was manual total station days. BS plumb bobs often back then. Now days with equipment like it is if you get less than 1:50000 in most situations I say something is wrong. The equipment if in adjustment and a decent layout of the traverse should yield better than that easily. My crews where getting way above that exception to irregular conditions like geometric shape triangular like lots small but a lot of vertical relief might get lower. But even then I would have some angles turned again. My LS rule was 1:40000 period.
TG my state (Oregon) does not express accuracy standards in terms of closures. If it did I wouldn’t worry about it. The thing is to perform your work in a manner that will achieve good closures, not to dogmatically loop your traverses and calculate closures.
I’ve been a StarNet disciple since 1997. I adjust and analyze almost everything I do. But I haven’t performed a CR adjustment and loop closure calc in all that time.
If you hit the minimum closure standards on a small lot in a monumented subdivision, holding original mons, that’s fine, but, if I’m doing a larger boundary for development purposes, just hitting the minimum standards are not good enough for me as I know that I will be staking millions of dollars in construction and I want my control as tight as I can get it.
The time is money approach only goes so far, If I have to take a loss by investing more time for quality purposes, so be it. Most projects that I work on stay in house from beginning to end. What I lose on the front end to assure quality, I can almost always make up on the back end on the layout side.
In the end, it’s all about doing quality work using the right equipment and best practices. Using the right equipment and methods on most average sized projects should have you exceeding minimum standards.
CR adjustments are pretty much gone these days with the variety of more modern methods and software. I can remember being trained in Trimble GPS processing by our resident guru, if the data didn’t pass the least squares Chi test, it was time to tear everything apart.
Thinking more of rural boundary work and would want better than state minimum standards, but they are what they are.
Say you survey a large tract with a decade’s old description with bearings and distances (chains or poles), and maybe some trees and/or fence posts for corners. All you find is one or two of them. You can have a great traverse, but now you are calculating where to set some new pins based on the theoretical center of a gnarly fence post or tree (maybe a leaner) that has probably doubled in size.
I think you are thinking correctly by not just trying for the minimum standard. It is why many as mentioned above from others now perform a least squares adjustment to analyze the data or observations. This makes it much easier to understand the uncertainty in any position point monument etc that are observed during your field work. StarNet probably led the way before almost anyone years ago for sure. It is probably still one of the better programs for the Land Surveying side of the house for what it does. It does it well. Compass Rule is still being used by a lot surveyors I talk with. But it doesn’t do what least squares can do for sure. If least squares is properly used. It took me a couple years on almost every job we did to prove least squares to my old boss. But once it clicked he was all in. I believe compass rule was very good because you could do an adjustment basically in the field book with just a basic calculator. Now that we have more power and computers along with many different measurement tools least squares makes more sense. I can remember typing in from field notes into starnet my ZA slope distance hz angle etc. even taped distances . Now data collectors have all that information in it.
For rural surveys, I want the 2 sigma positional accuracy to be about the diameter of a 5/8 in rebar for all monuments. Again for rural, not urban or suburban, I can tell a party chief that if his EOC could fit on the top of a rebar, all is good.
I appreciate incredibly precise measurements and enjoy making them, but would not rerun a rural survey that closed 1:10000.01 if the monuments were described in detail (set or found, size, material, and relationship to grade) with an accurate tie to the state plane coordinate system so the GIS dudes get the tax map right.
I appreciate incredibly precise measurements and enjoy making them, but would not rerun a rural survey that closed 1:10000.01 if the monuments were described in detail
Agreed. At the LSAW conference last week, the always-informative (and always-entertaining) Gary Kent again reminded us that a retracement survey can be no more accurate than the original. We have a responsibility to meet minimum standards, but of course the most critical thing is to recover/re-establish monuments in their original position, based on the evidence.
I’m a self-admitted millimeter chaser, but when it comes to boundary work I have to put the measurements second and the retracement first.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil PostmanI think @rover83 and @murphy nailed their points. I believe this is why the ALTA relative position tolerances not a bad guide to follow. .07 + 50ppm. The boundary retracement itself has little to do with our measurements in the big picture. Now nothing in surveying is absolute. If the retracement is intended for a design project say commercial shopping center one might want to tighten up the control etc a bit more not to say one neglects the boundary evidence and procedures to the point of relying on just measurements. You can do both.
Rover,
I agree with your quote of Ken regarding original surveys. Those monuments are the first expression on the ground of the intent of the owners. You can not improve on perfect. I do see the impact of ignoring this statement on a regular basis.
Even our relatively young state was originally surveyed in a fairly crude manner. The expression of the measurements was rough, and the monuments failed to survive the ravages of time. Along came the mathemagicians, fixing those ‘poorly executed’ surveys and putting the corners in a better, more perfect place. These ‘improvements’ reassigned land from one owner to another, leaving behind a path of destruction.
Our measurements absolutely should be expressed better than those from generations past. We will never survey ‘better’ than the undisturbed original monument of record…
For instance, your state minimum standard for unadjusted closure is 1:10,000. Do you have a higher personal unadjusted minimum that you require of your crews? Do you adjust every traverse?
My state has a closure requirement, if that is the method you select to follow, of 1:5,000 or 1:10,000 (rural/urban). With modern equipment and just a modicum of attention to the process of traversing, those numbers are easily outpaced. Most often, I see numbers in the 1:50,000 to 80,000 plus range. I would not consider that a higher personal standard, just that the requirements are the minimum and may need to be relied upon at their minimal amounts on occasion.
No, I do not adjust every traverse. If I hit 1:50,000 on a four sided traverse of about 400 feet per side, I would be adjusting about a hundredth at each corner – a value that IMO is not worth chasing when the physical monuments measured are significantly larger in diameter than the adjustment.
What if the crews usually average 1:20,000-35,000 for general boundary work and they bring in a 1:10,500 traverse on a boundary survey. Do you accept it as is and move on, adjust it, or send them back out to check? Under what circumstances would you have them re-shoot the traverse? Accuracy is always good, and time is money.
For me, the answer to this would depend on what the crew usually is working on to get to their average closures compared with what they had the lower closer value on. For example, if their closures of 1:20-35,0000 are on the same type of project (size, terrain, etc…) as the lower closure one, I would probably have some concerns and re-visit the lower closure site for peace of mind that there is not an equipment problem or a mistake as there would be no significant change in site conditions to cause a lower closure (or even better run some checks in the parking lot before wasting time running the traverse a second time with an equipment issue).
If the usual projects are different from the outlier, I would consider if the outlier project has some potential features that could influence lower closure out of the same crew. For example, if surveying tracts that are 5 acres of open ground with minimal relief is the usual, the crew probably have good practice at this type of project. If the same crew then has a rare need to survey a 50 acre (or even a 1/2 acre) lot that is very steep and wooded, even just inexperience in the best choices for traverse points or not choosing to chop a better line of sight instead of placing several extra traverse points can drag the closure numbers down. Both the 50 acre or the 1/2 acre scenario opens up the possibility of potential training to help the crew gather experience in best methods to approach different projects or possibly reflection by leadership to decide if traditional traversing alone was the appropriate method for the project.
If the results were within standards, the circumstance I would have them re-shoot would be either if the closure was low enough that I suspected a mistake (error wasn’t consistent with reasonable expectations of error given the specific traverse and equipment) or the error was large enough that adjustments would be larger than I was comfortable with for the specific project – a personal preference and would vary by project specifics. If all monuments were found, checked well with off site monuments, and compared well with record calls (all subjective matters), I would be less concerned about the lower closure number. If I had to calculate and reset monument(s), I would prefer that be done from tighter control – so I might look more critically at the lower closure.
Your measurements can be down to the Knatt’s anus but they are secondary to found, undisturbed, called for original monuments that are found and should be honored. Keep in mind that there are two different kinds of corners, legal corners (as called for in a deed with no reference to anything set) and found corners that are called for in the original deed and shown on the original survey.
The found corner will almost never match the deed or measured dimensions but are the paramount evidence of the original intent. If they differ considerably from the legal corner location, they control and should be held before even thinking about establishing a network for control on any type of project.
1:10,000, 1:20,000, etc., often becomes irrelevant with today’s use of GPS, where probability comes into play. In the end, our measurements are not superior to cruder measurement from days gone by.
If I am understanding this correctly you are saying have good procedures (3rdpoint checks, measures sets, Hit points with RTK as well) as a standard practice rather than close every loop? I was curious about this because where I live certain surveys would take several extra days just to close the loop. Which seems outrageous. For example boundary surveys in Marin county (steep, snaking narrow roads, lots of relief, very poor line of sight, copious foliage to battle, PITA neighbors) would take an unbelievable amount of times and effort to close. (Does LA Steven still lurk here?) Also its rather treed in there so that starting and closing on GNSS pairs often isn’t realistic either
And my place of work we never ever close loops unless something has gone horribly wrong. Usually long term staking jobs. Once I started studying surveying I started going hmmm. My boss more or less said “Hey people don’t want to pay for a survey to begin with let alone 2 extra days of fieldwork just for the closure.” I do have pretty good procedures tho and I run a tight ship as a crew chief I guess it goes back to the cheap, good or fast pick two philosophy.
I would love to learn to use LSA as it appeals to my nearby acronym OCD. But if you really get down to it how much of a difference is this making in a standard residential topo with record boundary? And isn’t it possible that we are smearing error into a very well measured position? Pardon my ignorance I am eager to learn with one to teach me.
Personally when I tie two points from opposite ends of my trav and they are hitting the record dimension reasonably well I’m feeling pretty good.
Thanks is advance guys. I am the head crew chief (LSIT) in my office training the younger guys and I think my boss would rather jump off the nearest bridge than teach me anything.
- This reply was modified 1 month, 3 weeks ago by surveylife.
- This reply was modified 1 month, 3 weeks ago by surveylife.
- This reply was modified 1 month, 3 weeks ago by surveylife.
California is a recording state, so many of the monuments you tie have measurements that are of record. Comparing your measurements to those of another is a form of closure.
BTW, closures are one thing, blunders are another. Things like 3rd point checks are done to catch and correct blunders. They have little to do with closures. You don’t consider closures until you have eliminated all the blunders. If you are using halfway modern instruments that are in good order competently, and eliminate the blunders, you can hardly help but meet minimum precision standards.
- This reply was modified 1 month, 3 weeks ago by Norman_Oklahoma.
@ surveylife
If I am understanding this correctly you are saying have good procedures (3rdpoint checks, measures sets, Hit points with RTK as well) as a standard practice rather than close every loop?
I don’t see any benefits of using a closed loop traverse over a closed link traverse unless the former is tied to an established point.
MH“Keep in mind that there are two different kinds of corners, legal corners (as called for in a deed with no reference to anything set) and found corners that are called for in the original deed and shown on the original survey.”
Can you elaborate or rephrase? I might be misreading this or having a brain cramp. Are you referring to trees, and other natural object as ‘legal corners’, and everything else – pins, stakes, set stones, etc. as ‘found corners?
last post was for chris-bouffard
- This reply was modified 1 month, 3 weeks ago by Stillplumb.
Judges don’t care about math as much as they care about original marks because the point of a survey is to discover the original intent of granting the land which is done through monuments. A measurement can sometimes be wrong, a monument never will be.
It’s why boundary surveying needs a finer approach than engineering. With engineering, you can always have one correct answer, with cadastral, you can end up with more than one.
I’m not sure how much benefit there is to using high precision instruments in cadastral surveying since it is, more often than not, not beneficial to the parties involved. Boundaries should be a bit more fuzzy to save on litigation and the heartache that comes from boundary disputes. The UK has no cadastral system and the country is still ticking along just fine.
Boundaries are not a mathematical expression, they are a social relationship between people and land. If two neighbours agree on where a boundary is, no one can dissuade them otherwise because ultimately, they are the ones that define the boundary, not some lines on a plan.
I don’t want to speak for Chris B.
However, I think what he is referring to as a legal corner are corners not set in orig survey, but legally contemplated such as lot corners in a subdivison, where only block corners were orig monumented, or section sub corners in PLSS.
Can we please repeat this over and over
I’m not sure how much benefit there is to using high precision
instruments in cadastral surveying since it is, more often than not, not
beneficial to the parties involved. Boundaries should be a bit more
fuzzy to save on litigation and the heartache that comes from boundary
disputes
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