Looking at a corner record filed with the State and County by a DOT employee who happens to be licensed as an LS.?ÿ The specific corner is in an intersection with stop lights in all directions, multiple lanes and concrete pavement.?ÿ I have used this corner when it was a much less important spot for traffic and the pavement was chip and seal.?ÿ Different monuments have existed over time starting with a stone in the 1800's that somehow became a railroad spike in a gravel road then became an iron bar in chip and seal, then a concrete nail in temporary conditions and finally a 1/2 inch iron bar in the latest reconstruction with the concrete surfacing.?ÿ The current corner record provides distances from the bar to the near face of the four signal light posts.?ÿ These are tapered aluminum posts atop a concrete base roughly one foot above road grade.?ÿ No information is provided as to where on the post the measurement was taken.?ÿ Assuming the post base would seem to be the most logical. You can forget that idea.
Tape from the bar found to each post at the base.?ÿ Numbers are sort of similar to record but somewhat consistently off.?ÿ Set on the bar with total station and shoot all four posts at the base.?ÿ Again, the numbers are sort of similar to record but somewhat consistently off.?ÿ Set up the GPS gear.?ÿ Go to each post, set the pole on the concrete base and lean the receiver against the near face of the post, knowing you are getting a distance that is not the distance to the face of the post.?ÿ Bammmm.?ÿ Near perfect agreement with the record.
Add roughly three-tenths to allow for the radius of the receiver and you have a?ÿ horizontal distance from the bar to the near face of the post at a spot somewhere around eight feet above ground level, but nowhere else along that tapered post.
First noticed erroneous distances years ago when total stations were dominant.?ÿ Placing the back side of the prism against an object does not provide the true distance to that object.?ÿ It is similar to what another surveyor would get using the same method with the same style of prism but not necessarily the same number.?ÿ It is not the true distance.?ÿ Introducing the difference between the edge of a receiver and the location of the shot recorded adds far more sloppiness into the record.?ÿ Reporting a slope distance to the base of the post on the near face is far more accurate for repeatability.?ÿ Takes a second worker, though, to pull the tape taut and accurately find the near face.?ÿ A far superior location for any method should have been selected away from the tapered posts.
Some guys consider the purpose of references to merely be an aid to finding the monuments. Others as a means of restoring the monument to its exact position once destroyed. I'm with the latter camp. But I'm not aware of any express statement of which is appropriate in OK statute. Corner Records are the express arena of the County Surveyor in Oregon, and very rarely used in my area of Washington.?ÿ
The need to indicate whether horizontal or slope measurements are provided suggests actual distances reported can be duplicated by using one of the two means depending on which is reported.?ÿ Screwing things up by roughly three-tenths of a foot to a somewhat randomly selected point is not helpful.
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PERPETUATION
1. Ties to government corners must be filed for record as provided by KSA 1987 Supp.
58-2011 and shall indicate whether the tie measurements are horizontal or slope.
I see no problem, get a shot at the base of each pole facing the opposite pole, then shoot again at 4' or 5' up. Proportion each cross pair of distances and see how close that agrees with the actual cross distances at some height on all poles.
Paul in PA
Accessories are part of the monument. If you cant get within three tenths on your ties you really shouldn't be surveying. Measurements arent the end all but it's just not that hard to do it right.
This is especially troubling, as in this case, when you are seeking a specific iron bar in a concrete reinforced area such as road bed or bridge that has been overlain with a couple inches of asphalt.?ÿ Just how much asphalt are you willing to chip away to hopefully be able to see the tip of the bar??ÿ In this case it would be an area roughly 15" by 15" thanks to the sloppiness of the reported ties.
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About 15 years ago some brilliant surveyor from a great distance off came to the rescue.?ÿ He discovered by using excellently maintained ties that a certain center corner was marked with a MAG nail and washer instead of a minimum of a 1/2" iron bar two feet in length.?ÿ So he removed the inferior monument, drilled a hole and placed the preferred bar.?ÿ Sounds good, right??ÿ Wrong.?ÿ The corner fell in the middle of Main Street directly over the center of a concrete reinforced box culvert that had been there since the 1920's.?ÿ The first six inches of the bar was in concrete but the other 18 inches was hanging in open air waiting to serve as an obstruction to catch trash from the flowing water gushing through the culvert.?ÿ The tip of the bar was far more difficult to see than the pre-existing MAG nail and washer.?ÿ His attempt to install a plastic cap was a major fail that had disappeared within a few months.?ÿ That problem no longer exists.?ÿ The old culvert has been replaced and I was called upon to preserve and then reset a monument.?ÿ Trust me, it is not a bar dangling into the culvert's water flow area.
That is a good solution to the problem, but I wouldn't say there is no problem.
Which is why I am a proponent of not reporting dinstamce to the 0.01' when allowable by regulations.
That bar is not in the center of the intersection by roughly 12 feet. A line between say the NE and SW posts would be nowhere near the bar's location.
I'm not sure that I understand the problem.?ÿ Why do you need to rely on arbitrary corner ties to find the paved over point? Are section corners not required to be tied to the state grid system?
Absolutely not and I may retire the day it becomes a requirement.?ÿ Coordinates are a joke.?ÿ Those with weak minds will never actually see a monument ever again.
From your post and comments, I have the impression that PLSS corner reference ties are more of a joke.
I used to share your opinion concerning Grid tie requirements. At least in NC, where our licensing board is comparatively active, Grid ties and the resulting coordinate labels have improved to the point of being extremely beneficial.
Like many, my favorite part of the job is the search for old corners. Grid ties have taken this aspect of surveying away from me. Most surveys begin with a couple of Grid coordinates that put me right on a corner or two. From there I can either run with it if it's within a couple of tenths or translate and rotate if it is an older datum. Either way, it's a lot faster than it used to be.
That day may be closer than anyone realizes.
I was going to remain quiet on this subject..but here goes. I have (and will always be) been a proponent of favoring the monument. As the years have rolled past I can see a 'shift' in the sentiment of my fellow practicing surveyors toward the use of a "derived" location for controlling monuments. That reduces a corner to a "calculated location" and in my mind places it lower on the dignity of calls list.
Not that there isn't a place for such things. I know of several section corners that are almost inaccessible due to traffic. While it is much easier to locate all the x's on the T/C and use the corner reference material to calc a spot, it is not without compounded error depending on which of the references you use. In this case the error is small and manageable, but error nonetheless.
I foresee litigation where a corner's recorded (published and utilized) coordinates are in conflict with a physical monument whose pedigree can be substantiated. I probably won't like the outcome. Thank God my tenure is drawing to a close.. 😉
Historically, SPC, UTM, or other such coordinates were not reproduceable at a practical precision for most property corners. I read in McEntyre's book 38 years ago an example of getting SPC for a land corner, miles from C&GS tri stations, and thought it could never catch on because of the accumulated error.
Now careful work with GNSS can pretty reliably repeat a point with good enough accuracy to reset a missing PLSS corner, IF both the original and the retracement take good data and match datum realizations, etc.
Coordinates can and will eventually move up in the list of evidence.?ÿ It will take many years of recording coordinates with proper metadata before a retracing surveyor frequently has good historical coordinates to check in retracement.
I don't think a lot of field crews are careful and trained enough at this point for it yet. A quick RTK?ÿ shot under canopy won't cut it. Too many today will misinterpret datum realizations.
When I think I think about the education level of field crews I remember the guy doing street topo near my home, who I asked if the elevation numbers on a stake his company had set were NGVD29 or NAVD88. He told me they used NAD83. I wouldn't trust him to set out horizontal coordinates recorded in an old datum realization.
We are already beginning to see those mythical corners being used. A statement of "not recovered this survey" admits this lack of diligence.
I do not trust coordinates. Period. I also do not trust all corner records. Most will seek out the last record on file and believe it to be correct. Some dumb bass who wouldn't be smart enough to poor pi** out of a boot stuck one 80 feet from the true corner monument that really does exist then filed a report. Fellow dumb basses will accept that as gospel and roll on. Our profession is becoming nothing more than a minor trade when this is labeled as acceptable behavior.
