roger_LS, post: 415901, member: 11550 wrote: Ok. So what I'm hearing is that the only time you'd be using it to determine final boundary coordinates might be when you had a monument, then a bunch of missing courses then another monument and could then force record onto these two monuments either by holding record angular relationships or by letting both angle and distance float. But this could also be used to solve for just one corner. Maybe this is what I'm seeing on these maps, but they forgot to include a note and left it unintelligible.
I wouldn't say that. Take the problem of reconstructing the Engineer's Centerline on a typical State highway. There are lots of markers indicating approximately by ties from them where the centerline was run, even though nearly all are inconsistent with markers opposite them on the other side of the right-of-way. In other words there is a surplus of evidence, none of which is conclusive in and of itself. That is a problem that least squares can generally solve well if you set it up correctly.
That is one example of retracement, i.e. using lots of slightly erroneous data to reconstruct the more exact underlying pattern.
A familiar problem may be trying to reconstruct a boundary from markers that have been shifting from soil movements as is typical when highly expansive clay soils go though a few wet and dry cycles. After a few years, some of the markers set on slopes will probably have migrated down the slope with the top 48 inches of soil. Marker movements in flatter areas may show a random walk pattern. When the problem is to reconstruct where the markers were originally, before they were shifted out of place, the exercise is finding a way to model the theoretical shape and location of the original boundary in a way that deals with the obvious movements of the markers from their original positions.
Kent McMillan, post: 415910, member: 3 wrote: I wouldn't say that. Take the problem of reconstructing the Engineer's Centerline on a typical State highway. There are lots of markers indicating approximately by ties from them where the centerline was run, even though nearly all are inconsistent with markers opposite them on the other side of the right-of-way. In other words there is a surplus of evidence, none of which is conclusive in and of itself. That is a problem that least squares can generally solve well if you set it up correctly.
That is one example of retracement, i.e. using lots of slightly erroneous data to reconstruct the more exact underlying pattern.
A familiar problem may be trying to reconstruct a boundary from markers that have been shifting from soil movements as is typical when highly expansive clay soils go though a few wet and dry cycles. After a few years, some of the markers set on slopes will probably have migrated down the slope with the top 48 inches of soil. Marker movements in flatter areas may show a random walk pattern. When the problem is to reconstruct where the markers were originally, before they were shifted out of place, the exercise is finding a way to model the theoretical shape and location of the original boundary in a way that deals with the obvious movements of the markers from their original positions.
Got it, that's complex. So this "best fit method" takes a bunch of monuments then weights them with some mathematical formula in some way then constructs a best fit that somehow adjusts record by the monuments without actually honoring the position of any of them. So I take it this is an extreme last resort, like proration gone wild.
roger_LS, post: 415911, member: 11550 wrote: Got it, that's complex. So this "best fit method" takes a bunch of monuments then weights them with some mathematical formula in some way then constructs a best fit that somehow adjusts record by the monuments without actually honoring the position of any of them.
In the case of the right-of-way of the typical Texas rural highway constructed before maybe 1990 (my guess as to date of changeover in TxDOT procedures) there are no original monuments, only the precast concrete posts that the road contractor installed without any amazing diligence in the effort. However, there is reason to think that they were installed in positions that were nominally at plan distances from the Engineer's Centerline, which was originally marked upon the ground and perpetuated during construction. If you consider, as I do, the Engineer's Centerline to be the controlling location line for a strip of land that was described entirely in relation to it, then the retracement task is one of finding the location for the Engineer's Centerline that agrees as well as possible with the evidence, which on many highways is mostly just the haphazard precast posts in various states of disarray. Some will be intact and plumb, most will be obviously out of whack: either leaning well off plumb, broken, pushed by machinery, or simply removed by farmers or utility construction. So any method of reconstruction will have to take that into account.
Kent McMillan, post: 415908, member: 3 wrote: In PLSSIa, I do imagine that there is the luxury of being able to even think about dealing with just a line at a time, but in typical retracement problems in Texas that would not be a successful plan for a resurvey.
For example, there is a series of surveys made along the Rio Grande for the Texas & Pacific Railroad Company running upstream from Presidio where extensive obliteration of the orignal marks has been commonplace. The surveys were located from traverses run along the river, marking corners at 950 vara intervals along the river front which were mostly either washed away or farmed out. Patents issued on surveys made in 1887 or so that are mostly phantoms as a result of the obliteration of evidence. While the grants ran back from the river for two miles, they terminated in the desert a corners "marked" by completely fictitious monuments, none of which were set.
The best physical evidence that remains of the original surveys are just a bare few rock mounds that happened to have survived and miles of nothing in between. The best record that perpetuates the original surveys is itself nearly a phantom, a traverse run a century ago when some of the marks and their bearing trees could be identified but which itself was only tied to a bare few things that still exist.
Trying to reconstruct each line of each survey in sequence would be an exercise in complete futility since part of the exercise dealt with the fact that the original suveyor was using a wildly incorrect variation in his compass and part of the exercise is to arrive at the most reliable measures of the actual direction of his "North" at various points along the phantom of his survey.
In other words, the only way to solve the problem is to deal with very many lines run by at least a couple of surveyors in a comprehensive way which includes bootstrapping the effort by deriving his "North" from his calls for bearings to topo features like peaks from the positions of long-vanished markers, a "North that is used to compute those positions.
So many interconnected, dependent parts related by a survey means there is no option not to deal with the whole pattern.
What you are describing sounds much closer to PLSS surveying than you may realise.
aliquot, post: 415915, member: 2486 wrote: What you are describing sounds much closer to PLSS surveying than you may realise.
Except in PLSSia, isn't every marker ever set in some location that wasn't marked by the actual government survey an "original" monument? :>
Kent McMillan, post: 415916, member: 3 wrote: Except in PLSSia, isn't every marker ever set in some location that wasn't marked by the actual government survey an "original" monument? :>
No. The unmarked corners were fixed in place by the original survey( or official resurvey ). These locations can be subject to "movement" due to bona fide rights tied to a subsequently set marker, but bona fide rights are can only be applied in limited circumstances, not including a survey that utilized innapropriate methods for the time.
aliquot, post: 415920, member: 2486 wrote: No.
I'm pretty sure that I've been reading just that for years now. When did Jeff Lucas decide to hoe a different row?
Kent McMillan, post: 415922, member: 3 wrote: I'm pretty sure that I've been reading just that for years now. When did Jeff Lucas decide to hoe a different row?
I don't think he has. He is often wrong.
Kent in the plss....
Thats vara bad medicine.
roger_LS, post: 415848, member: 11550 wrote: I am curious how least squares is being used amongst surveyors out there. I've always thought of it as a tool to adjust systematic errors out of ones survey, but am wondering to what extent it may be being used to determine final boundary placement. From time to time I've picked up maps and been perplexed about how a specific corner was reestablished; record bearings weren't held, neither were record distances, proration not used. There seems to be no rationale behind anything. So I'm wondering, are there folks out there using least squares to actually create final boundary positions?
www.primacode.com
Transform
The help file for Primacode Transform answers many of the questions in this thread:
http://www.primacode.com/downloads/TransformHelp.pdf
I generally use Star*Net to calculate from the written record for "recon" -- i.e. what do we expect to find out there? Also to find typos in the record.
Then use Star*Net in its more intended capacity to reduce the field measurements. I don't mix the field with the record, or if I do I "free" all the record stuff so it is only in the file as a comparison to the field measurements.
Then use Primacode to compare the record with the field data and decide what to accept as undisturbed or an accurate perpetuation.
Especially useful in a large old simultaneously conveyed plat.
Primacode is also very useful for the forensic-type stuff, knowing that a plat was laid out using a short chain, etc. It even becomes possible to see when a surveyor has included measurements from record on a map, because they don't scale the same as a fieldwork.
Primacode gives a confidence level for the scaling it finds when matching a coordinate system calculated from record to new measurements.
It makes for less pincushioning and a better narrative.
(edit for typo)
roger_LS, post: 415911, member: 11550 wrote: Got it, that's complex. So this "best fit method" takes a bunch of monuments then weights them with some mathematical formula in some way then constructs a best fit that somehow adjusts record by the monuments without actually honoring the position of any of them. So I take it this is an extreme last resort, like proration gone wild.
Backwards, kinda. It takes a bunch of field observations (as coordinates) and finds the best fit of the record to those monuments. It does not adjust the record, it helps decide which found monuments fit the intent of the record and how closely.
Kent McMillan, post: 415908, member: 3 wrote: In PLSSIa, I do imagine that there is the luxury of being able to even think about dealing with just a line at a time, but in typical retracement problems in Texas that would not be a successful plan for a resurvey.
For example, there is a series of surveys made along the Rio Grande for the Texas & Pacific Railroad Company running upstream from Presidio where extensive obliteration of the orignal marks has been commonplace. The surveys were located from traverses run along the river, marking corners at 950 vara intervals along the river front which were mostly either washed away or farmed out. Patents issued on surveys made in 1887 or so that are mostly phantoms as a result of the obliteration of evidence. While the grants ran back from the river for two miles, they terminated in the desert a corners "marked" by completely fictitious monuments, none of which were set.
The best physical evidence that remains of the original surveys are just a bare few rock mounds that happened to have survived and miles of nothing in between. The best record that perpetuates the original surveys is itself nearly a phantom, a traverse run a century ago when some of the marks and their bearing trees could be identified but which itself was only tied to a bare few things that still exist.
Trying to reconstruct each line of each survey in sequence would be an exercise in complete futility since part of the exercise dealt with the fact that the original suveyor was using a wildly incorrect variation in his compass and part of the exercise is to arrive at the most reliable measures of the actual direction of his "North" at various points along the phantom of his survey.
In other words, the only way to solve the problem is to deal with very many lines run by at least a couple of surveyors in a comprehensive way which includes bootstrapping the effort by deriving his "North" from his calls for bearings to topo features like peaks from the positions of long-vanished markers, a "North that is used to compute those positions.
So many interconnected, dependent parts related by a survey means there is no option not to deal with the whole pattern.
Which is not the same as tossing a geometric figure into LS as your sole evidence. If you didn't bother looking for any corners or long standing possession, you didn't survey it. If you did, then you didn't use LS as your only evidence. I suspect you knew that, you just wanted another dig at a system you don't understand.
thebionicman, post: 415949, member: 8136 wrote: Which is not the same as tossing a geometric figure into LS as your sole evidence. If you didn't bother looking for any corners or long standing possession, you didn't survey it. If you did, then you didn't use LS as your only evidence. I suspect you knew that, you just wanted another dig at a system you don't understand.
Actually, in the example along the Rio Grande that I mentioned, there is no remaining evidence of the original survey on a series of surveys. The survey measurements along the lines run by both the original surveyor and subsequent surveys are the best evidene of where the surveys were originally located. So the surveying work focuses correctly upon how to best use those measurements to reconstruct the surveys. It turns out that least squares is the superior method for that. It is not a one line at a time exercise.
Kent McMillan, post: 415954, member: 3 wrote: Actually, in the example along the Rio Grande that I mentioned, there is no remaining evidence of the original survey on a series of surveys. The survey measurements along the lines run by both the original surveyor and subsequent surveys are the best evidene of where the surveys were originally located. So the surveying work focuses correctly upon how to best use those measurements to reconstruct the surveys. It turns out that least squares is the superior method for that. It is not a one line at a time exercise.
So you restored the lines without looking for any physical evidence on the ground, then set monuments without checking at your calculated points?
Least Squares Schmeast Squares is for wussies...
You make a giant 1:1 map of the Plat or Township you are surveying out of fairly rigid steel wire. Then you heat the wire to red hot temperature. Next you bring in your fleet of helicopters which picks up the grid, you will need a battalion of the highest most highly skilled chopper pilots, the ones who flew in Nam but were all busted down to private because they spent their whole time over there breaking all the rules and annoying rigid by the book Generals...your helicopters pick up the red hot wire "Plat" and fly it to the scene using the RTK gps in their choppers and drop it down burning through the houses, fences, sheds, trees, shrubs, and everything in the way down to the ground. Now you know where the boundaries are located.
half bubble, post: 415941, member: 175 wrote: The help file for Primacode Transform answers many of the questions in this thread:
http://www.primacode.com/downloads/TransformHelp.pdf
I generally use Star*Net to calculate from the written record for "recon" -- i.e. what do we expect to find out there? Also to find typos in the record.
Then use Star*Net in its more intended capacity to reduce the field measurements. I don't mix the field with the record, or if I do I "free" all the record stuff so it is only in the file as a comparison to the field measurements.
Then use Primacode to compare the record with the field data and decide what to accept as undisturbed or an accurate perpetuation.
Especially useful in a large old simultaneously conveyed plat.
Primacode is also very useful for the forensic-type stuff, knowing that a plat was laid out using a short chain, etc. It even becomes possible to see when a surveyor has included measurements from record on a map, because they don't scale the same as a fieldwork.
Primacode gives a confidence level for the scaling it finds when matching a coordinate system calculated from record to new measurements.It makes for less pincushioning and a better narrative.
(edit for typo)
Ok. So it can be valuable as an analysis tool, similar to the traditional model of taking a bunch of inverses between found monuments and comparing to record to look for patterns.
half bubble, post: 415943, member: 175 wrote: Backwards, kinda. It takes a bunch of field observations (as coordinates) and finds the best fit of the record to those monuments. It does not adjust the record, it helps decide which found monuments fit the intent of the record and how closely.
Alright, so this is when you've got a bunch of monuments but they are all garbage and you really don't want to hold anything but are under contract to do a survey. So you can keep a record configuration and approximate an estimated position on the ground.
thebionicman, post: 415955, member: 8136 wrote: So you restored the lines without looking for any physical evidence on the ground, then set monuments without checking at your calculated points?
No, the reconstruction generated search coordinates, but there was no remaining physical evidence. In some cases, it was obvious that the river had washed the corners out and no search was necessary. The bearing trees from the original survey in 1887 were mostly cottonwoods which had grown along the banks of the Rio Grande before the Elephant Butte Dam in New Mexico completely changed the flow regime in the river. There were no traces of most of those bearing trees reported even back in 1910, probably partly because they were either used to make low dams in the river to divert water into irrigation channels or were cut for timber.
Since then, the fringes of the river that in the late 19th century had been farmed as low irrigated fields without regard to the boundaries of the original suveys had grown up in tamarix. In the 1950s a fairly good surveyor had attempted to locate the original suvey lines and had failed not only to find any original mark, but had failed spectacularly to even get close to the pattern of the original surveys. What is there is a great bulldozed floodplain that is now grown up in tamarix. It is a situation where the obliteration has been so complete that the best evidence is the records of the original surveys and an extremely sparse record of recoveries made more than 100 years ago. Star*Net was a very good solution for recontructing what had become phantoms.
Another case where Star*Net is a truly brilliant solution is in downtown districts where the obliteration of evidence of the surveys made in the streets by the City Engineer has been nearly complete. In Austin, the City Engineer's work with transit and tape was excellent during the period from about 1913 through 1950 or so. There are, as a result very good records of networks that were surveyed across some districts that tied centerline monuments together that have since disappeared. If one can find and position a sufficient number of marks that remain, the adjustment of the transit and tape network via Star*Net is probably the best reconstruction possible.
