A client wrote today to ask about the "inaccuracies" of some old survey markers set in 1857 and 1914 at various corners of a ranch in which he has an interest, a tract composed of all of two original land grants made by the State of Texas that I'll call the PQR and XYZ Surveys, less certain lands previously sold to others. What I wrote in reply was essentially this :
"As to the accuracy of the rock mounds made by surveyors in the 19th and early 20th century, the operative principle is that where a corner was actually marked upon the ground when the land was originally surveyed is more important than the fact that the bearing and/or distance that the surveyor reported between the points where he marked corners is erroneous. So, an original, undisturbed rock mound made in 1857 to mark a corner of, say, the PQR Survey is the primary evidence of where that corner actually is and the fact that the 1857 surveyor may have reported bearings and distances that would place the corner in a somewhat different position yields to the fact of where he actually marked the corner on the ground.
The equipment and methods that the 19th and early 20th century surveyors typically used (compasses and chains) tended to produce somewhat inaccurate measurements even over ideal terrain. The steeply sloping terrain that the lines of both the PQR and XYZ Surveys cross means that the 19th century methods will inevitably result in significant errors in the distances and bearings that the surveyors reported.
For example, the Northwest line of the XYZ Survey was reported to be 498 varas in length nearly exactly 103 years ago when Travis County Surveyor H.G. Lee made the survey upon the strength of which the State of Texas relinquished its interest by issuing a patent to the land using the metes and bounds description that Mr. Lee prepared. A resurvey in 1951 found the distance between what were judged to be the rock mounds marking the corners of the XYZ Survey that Lee reported as being 498 varas apart were actually 492.50 varas distant and my modern resurvey measurements between the same two corners that the 1951 surveyor found in place show the distance to actually be 491.090 varas.
There is no reason to believe that the corners have moved by 6.91 varas (about 19 ft.) between 1914 and the present or by 1,41 varas (3.92 ft.) between 1951 and now. What has changed is that I have the ability to measure the actual distance with high accuracy using technologies that didn't exist in 1914 or in 1951."
And, of course, what I meant to type was:
"A resurvey in 1951 found the distance between what were judged to be the rock mounds marking the corners of the XYZ Survey that Lee reported as being 498 varas apart was 492.50 varas and my modern resurvey measurements between the same two corners that the 1951 surveyor found in place show the distance to actually be 491.090 varas."
This post actually brings up a question I've mulled around in my mind from time to time. And my inquiry is serious.
Are we to believe we are at a point in time that our measurements are at the pinnacle of accuracy? It does seem as though in the science of physical land measurements "we have arrived". I mean I conduct my surveys as if they are free of the cumulative blunderings of 1914 or even 1951. But didn't the surveyor in 1951 feel the same about his work and resurvey of the 1914 reports?
I know it's "splitting hairs"...but it makes me wonder sometimes. 😉
paden cash, post: 432825, member: 20 wrote: This post actually brings up a question I've mulled around in my mind from time to time. And my inquiry is serious.
Are we to believe we are at a point in time that our measurements are at the pinnacle of accuracy? It does seem as though in the science of physical land measurements "we have arrived". I mean I conduct my surveys as if they are free of the cumulative blunderings of 1914 or even 1951. But didn't the surveyor in 1951 feel the same about his work and resurvey of the 1914 reports?
I know it's "splitting hairs"...but it makes me wonder sometimes. 😉
Yes, I consider the surveys I do to be in "Final answer, Alex" territory as far as measurements go. It isn't just an opinion, but one based upon the deep technology that was behind how they were made. This is unlike the 1914 and 1951 iterations that were made by methods that were known at the time to be somewhat inferior.
However, on your main point : If I were relying entirely on RTK, I would have to agree with you that the future may just have a number of numerical surprises in store as other, more diligent, surveyors arrive.
The main thing that I see in play in the future is that an entire generation of surveyors will arrive to continue the work who are so preoccupied by running whatever the latest flavor of technology is that the real object of the exercise, i.e. to actually find the locations of lines and corners run on the ground in the remote past will become a matter of secondary or lesser importance.
Kent I'll weigh in from down under as you've touched on or described our situation to the mm.
Monuments are irrefutable if they are original and all the measurements under the sun doesn't alter the true boundary corner.
I tend to agree with Paden's comments and yet as you say Kent, future generations are at risk of measurement over monument.
I imagine, thinking as a current, contemporary surveyor, I'd still not just say "that's it, there's your corner" if I couldn't find the mark just because it appeared to not exist where it's supposed to, based on original surveys (measurements) of some long distant era.
That's where the "real" Surveyor's skills come to the fore.
What seems to be the problem though is the then disagreement between fellow surveyors over trifling different measurements, and voila, a "pincushion" spanning perhaps 50 to 100 mm over boundary lengths of 100's of feet, chains, metres etc.
I realise it's an area for much disagreement, and also one "where Angels fear to tread", but as a professional, surely we owe the profession and the clients/ landowners a professional outcome.
Are we "upholders of the cadastre" or upholders of our clients interest? To me there's a subtle difference.
I believe I'm charged with upholding the cadastre.
Caveat. That's a Tasmanian surveyors comment.
Edit: there's also Adverse Possession, but that's an entirely different argument and then that is "your clients interest".
Kent McMillan, post: 432829, member: 3 wrote: The main thing that I see in play in the future is that an entire generation of surveyors will arrive to continue the work who are so preoccupied by running whatever the latest flavor of technology is that the real object of the exercise, i.e. to actually find the locations of lines and corners run on the ground in the remote past will become a matter of secondary or lesser importance.
Kent, you and I may disagree on some subjects, but on this one I agree 100%. All the measurements shown on a plat or map are to get one to the corner. To paraphrase, "It is far better to have an incorrect measurement to the corner than an accurate measurement to where the corner was never intended to be".
Andy
paden cash, post: 432825, member: 20 wrote: This post actually brings up a question I've mulled around in my mind from time to time. And my inquiry is serious.
Are we to believe we are at a point in time that our measurements are at the pinnacle of accuracy? It does seem as though in the science of physical land measurements "we have arrived". I mean I conduct my surveys as if they are free of the cumulative blunderings of 1914 or even 1951. But didn't the surveyor in 1951 feel the same about his work and resurvey of the 1914 reports?
I know it's "splitting hairs"...but it makes me wonder sometimes. 😉
Nope, not there for sure, there are some even relying on ephemeral SPC, it's been amazing watching how quickly that system degrades, it's never been more important to have good monuments.
Measurements over monuments is nothing new, I have notes on one from 1880 and an early 20th century case repeats expert testimony about the City Engineer resurveying the entire City of Sacramento and setting stones at the new and improved locations of the street P.I.s in the 1870s.
I think Cooley's speech came about because the practice was widespread even then.
I can see some day in the future when the say the measurements we take today aren't very accurate and they can measure to an accuracy of better than 0.01'
Richard, post: 432834, member: 833 wrote: I tend to agree with Paden's comments and yet as you say Kent, future generations are at risk of measurement over monument..
I'll observe that part of my confidence in the small uncertainties in my work comes from returning to surveys that i made more than twenty years ago without GPS and finding the small errors in the work to be within what error analysis predicted at the time (i.e. Star*Net). Is the survey that I described to my client numerically perfect? No, obviously not. I estimate that the distance between the axles in the rock mounds that I determined to be 491.090 varas has an uncertainty of 0.014 vara (0.04 ft.) at 68% confidence), so it's entirely possible that some future surveyor will find a distance that differs by some value in the range of 0.00 to 0.04 ft. from what I'll report. Likewise, since the bearing I've determined has an uncertainty of 0?ø00'06" (also at 68% confidence). There will be differences.
However, unless humans shrink to the size of mice, uncertainties of 0.04 ft. are unlikely to have any greater significance 100 years from now than they do today for suburban land use. If I'm wrong about that, fortunately I won't be around to care.
Kent McMillan, post: 432876, member: 3 wrote: I'll observe that part of my confidence in the small uncertainties in my work comes from returning to surveys that i made more than twenty years ago without GPS and finding the small errors in the work to be within what error analysis predicted at the time (i.e. Star*Net). Is the survey that I described to my client numerically perfect? No, obviously not. I estimate that the distance between the axles in the rock mounds that I determined to be 491.090 varas has an uncertainty of 0.014 vara (0.04 ft.) at 68% confidence), so it's entirely possible that some future surveyor will find a distance that differs by some value in the range of 0.00 to 0.04 ft. from what I'll report. Likewise, since the bearing I've determined has an uncertainty of 0?ø00'06" (also at 68% confidence). There will be differences.
However, unless humans shrink to the size of mice, uncertainties of 0.04 ft. are unlikely to have any greater significance 100 years from now than they do today. If I'm wrong about that, fortunately I won't be around to care.
Unless you anchor your monument to bedrock 20' down there will be movement and even then there will be some movement.
I agree, I follow Jim Conkright (1970s and 1980s) and never miss by much unless he blundered (I've found a few set out calculation blunders because we have his files). I measured a mile he did with transit and tape in 1971 and hit flat but I disagreed with his measurement to the quarter corner in the middle by a whopping 0.05 feet!
Then I've followed surveyors with total stations that the work is less than at an ideal accuracy. So it varies.
Measurement accuracy capabilities in the field will probably continue to improve. But as has been suggested in some of the earlier posts, we have reached a point where careful measurements can produce all the accuracy that is useful for land surveying.
It makes a visible difference to a land owner if a section miscloses by a chain, which was one of the earlier standards. It makes a difference to an urban lot owner if his wall is a few tenths off. It makes a difference in downtown Big City if the skyscraper can be another tenth wider. But will it ever matter to a land owner if his line is 0.01 off? Will the ground be stable enough to hold 0.01?
Right now the state of the art is probably what you read about being used for aligning high energy nuclear colliders, where they record measurements to 0.1 millimeter or better. They are nearly up against monument surface irregularity and geological stability limits.
In the Austin area, there are basically two soil conditions. West of the Balcones Fault, on the Edwards Plateau, the ground is limestone of some variety, either massive or weathered. Markers set in that area will be highly stable as long as they are initially stable, and not just driven to rejection in shallow soil, leaving half the marker in the air.
On the other hand, East of the Edwards plateau, the soils are commonly highly expansive clayey varieties in which it is a challenge to set anything that won't either random walk or migrate over wet-and-dry cycles, migration being expected on slopes. That is a situation where measurements can be much more reliable than markers as indicators of where corners were originally marked when boundaries were created.
Kent McMillan, post: 432884, member: 3 wrote: In the Austin area, there are basically two soil conditions. West of the Balcones Fault, on the Edwards Plateau, the ground is limestone of some variety, either massive or weathered. Markers set in that area will be highly stable as long as they are initially stable, and not just driven to rejection in shallow soil, leaving half the marker in the air.
On the other hand, East of the Edwards plateau, the soils are commonly highly expansive clayey varieties in which it is a challenge to set anything that won't either random walk or migrate over wet-and-dry cycles, migration being expected on slopes. That is a situation where measurements can be much more reliable than markers as indicators of where corners were originally marked when boundaries were created.
Of course, that begs the question as to how to deal with original corner monuments that appear to have migrated over time. Did the fence migrate the same amount in the same direction as the monument? Does a surveyor care enough to worry about that migration if the land owners seem satisfied with their corner locations? (I mean do they even know about it or have a need to know about it). (I think I have my own answers, but it's never black-and-white).
David Livingstone, post: 432871, member: 431 wrote: I can see some day in the future when the say the measurements we take today aren't very accurate and they can measure to an accuracy of better than 0.01'
Does this mean our "pincushion circles" will get smaller?
Tom Adams, post: 432887, member: 7285 wrote: Of course, that begs the question as to how to deal with original corner monuments that appear to have migrated over time. Did the fence migrate the same amount in the same direction as the monument? Does a surveyor care enough to worry about that migration if the land owners seem satisfied with their corner locations? (I mean do they even know about it or have a need to know about it). (I think I have my own answers, but it's never black-and-white).
In the typical situation, what migrates is the top 48 inches or so of the soil as deep cracks form in the dry season forming isolated pillars of clay soil. After a good rain, the moisture content of the soil at the base of the pillar increases first, losing compressive strength and causing the pillar to settle by gravity in the downhill direction, the cracks generally being approximately normal to the sloping surface of the ground, not plumb.
As the pillars of soil settle, they rotate in the downhill direction so that a survey marker or fence post that had been originally set exactly plumb will rotate downhil with the soil it is in. Fast forward many wet-and-dry cycles and the fences are obvious out of whack. Posts aren't close to plumb and that 30-inch pipe or rebar is also well out of plumb.
In other words, that marker leans so much that it looks disturbed and the fences obvlously appear to have suffered some force acting on them. It's not as if there are no clues.
paden cash, post: 432825, member: 20 wrote: This post actually brings up a question I've mulled around in my mind from time to time. And my inquiry is serious.
Are we to believe we are at a point in time that our measurements are at the pinnacle of accuracy? It does seem as though in the science of physical land measurements "we have arrived". I mean I conduct my surveys as if they are free of the cumulative blunderings of 1914 or even 1951. But didn't the surveyor in 1951 feel the same about his work and resurvey of the 1914 reports?
I know it's "splitting hairs"...but it makes me wonder sometimes.
As an addendum, I'll mention what I should have earlier. We've reached the point that a succession of technologies all give essentially the identical answer, but with a level of effort that gets progressively less with each generation of the technology.
For example, I believe that I could go out on the ground with 1970-vintage technology in the form of a theodolite, traverse set, and calibrated tape and measure the distance and bearing between the centers of the two axles that were subject of my original post and get an answer with the identical or better undertainty as the course between them calculated from GPS vectors to each axle does. It would not be quick or easy, though. It would take probably a couple of days with a chainsaw and loppers to prepare the line, at least a day to run the traverse between the points with one or two assistants, paraphenalia such at thermometers and tension handle, and two astronomical observations for azimuth at the ends of the traverse.
Fast forward to total station with EDM with 6mm standard deviation and there are still a couple of days of brush cutting over rough terrain, but it could all be done in a day with one assistant or alone. The astro observations at both ends of the traverse would still take the same amount of time.
So theodolite and tape and total station/EDM technologies give the same answer within the limits of the respective uncertainties.
Fast forward to about 2000 and use L1 GPS to tie between the same points instead of positioning them via vectors from a control point with a well-determined NAD83 position. That's a morning's work for one person.
At every point along the way, the three different technologies could produce the same answer (within the limits of the uncertainties). The main difference was operational. It took fewer people and less time to accomplish the task, but there was no major improvement in results. This is how one knows that the "Final answer, Alex" moment has arrived. It's now about simply about squeezing a few more minutes out of the process while maintaining the quality that was possible forty or fifty years ago by other methods.
Kent,
Wow - I was with you every step of the way through that progression. Well written, indeed. The ramifications of the increase in productivity become evident, vis-a-vis business models, both provider and regulatory agencies.
Warren Smith, post: 432982, member: 9900 wrote: The ramifications of the increase in productivity become evident, vis-a-vis business models, both provider and regulatory agencies.
In my view, as the minutes get squeezed out of the effort, the most important thing is to monitor the quality of what is actually getting done. I think that it is very fair, for example, to compare the flavor-of-the-day technology to what was possible more than thirty years ago by other methods. The obvious way to do that is via some sort of survey adjustment software (such as, say, Star*Net) that implements uncertainty analysis as well as facilitating the improvements in the rough spots by the simple expedient of just adding more observations.
Where things go to Hell is when the technology drives the view of what is possible. In other words, if one starts out with a certain plan to position whatever by some whatever method, then he or she may well conclude that whatever they end up with is as good as it gets without considering what could be done to improve it to what was possible forty years ago.
