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It's a goner...


Kewaneh & Shark
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see RY0075 for a very similar photo. i noticed that you logged this as "destroyed", as it clearly is. i've read in these forums that the only way to know if it is truly destroyed is to see the bronze mark out of place. the mark is now sitting on some chump's coffee table, and it's unlikely that i'll see it out of place. it's clear to me that GT1650 and RY0075 really are destroyed, and i would rather report mine that way, as it is more accurate. i have found several monuments broken in a similar fashion. should i change them from "Not Found" to "Destroyed"?

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Sixthings -

 

I wouldn't change any of the logs you've already made unless you know for sure that it is in fact destroyed. The rule of thumb that 'if you can't actually see it destroyed, don't log it a such' is a good rule to follow. If you're not certain, don't do it.

 

As you've read in the forums, the opinions about what constitutes destruction are quite diverse and discussions about the term 'destroyed' can get somewhat heated. The fact is that destruction means different things to different people. For most people it's a black/white issue with very little grey area. The logic goes like this: If they can see where it was, and it's not there, it must be destroyed.

 

Another fact however, that is not completely understood by many people outside the surveying and geodetic communities (there are quite a few people in these forums who do undertand it though,) is that the degree of destruction of a benchmark means different things to different benchmarks. It can be much more than just black/white and many times there is more grey area than not. Oftentimes, benchmarks have accessories to the monuments to help determine their locations. Those accessories, if intrepreted correctly, can re-establish the position of the benchmark, even if the brasscap (or whatever else was being used as the mark) is gone. Also, horizontal control points, have a higher chance at a possibility of being re-established from the accessories than a vertical control point would. (Many horizontal control stations, like triangulation stations, have reference monuments and underground monuments set with them to verify and/or re-establish their positions if necessary.)

 

My reasoning for logging GT1650 as destroyed was based on the facts that not only was the brasscap missing and concrete post shattered, but also that the concrete post had been displaced. It is described as being up 0.7' and set to the northeast of the 2"x6" witness post. I found it completely dug up and set to the west of the 2"x6" witness post. The other described witness post is also missing, but the underground cable warning sign remains, but it could have been moved. Also, on the original data sheet, the mark has a vertical classification of 'first order, class 2' (a high rating) and the elevation had been adjusted using the NGS's VERTCON system. This all told me that it was a mark used for vertical control, and the accessories were not of the type that could be used to re-establish this monument.

 

A good example of a damaged, but not destroyed horizontal control monument that you may find interesting is GU3441. I found it severely displaced, but logged it as a find anyway. There are accessory monuments described (that I was unable to search for) and there is a good chance that they still exist. If they do, the true location for the benchmark monument could be re-established from them.

 

Hope this helps.

 

Keep on Caching!

- Kewaneh

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quote:
Originally posted by Kewaneh & Shark:

I wouldn't change any of the logs you've already made unless you know for sure that it is in fact destroyed. The rule of thumb that 'if you can't actually see it destroyed, don't log it a such' is a good rule to follow. If you're not certain, don't do it.

- Kewaneh


Howdy, K&S! What would your opinion of this one be? It's obviously someone's souvenir now. And, the stability of the setting was questionable to begin with, as you can see in the photos. TIA.

 

Cheers ...

 

~Rich in NEPA~

 

1132_1200.jpg

 

--- A man with a GPS receiver knows where he is; a man with two GPS receivers is never sure. ---

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quote:
There are accessory monuments described (that I was unable to search for) and there is a good chance that they still exist. If they do, the true location for the benchmark monument could be re-established from them.


 

Kewanah --

 

So how 'valuable' are the old triangulation-station marks to the modern surveyor, anyway?

 

These days with GPS/WAAS survey instruments he'd just set a new one rather than re-establish a missing mark from the reference/azimuth/underground marks?

 

Here's the reason I ask:

I logged a 1940's tri-station on a local ridge. The owner said he will soon start construction of his new home on the site, but would try to work around the station mark if at all possible. (He didn't know he had one up there and was quite interested when we found it!)

 

It got me thinking about how valuable or useful

these tri-station marks are now that surveyors use GPS.

 

Thanks,

W. Wind.

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The tri-stations represent the highest order of precision obtainable through conventional ground based geodetic survey methods. Its true that expert use of GPS can now produce stations of equal or potentially superior quality, but the capacity to do this on a large scale comparable to the nationwide triangulation network is only now coming into existence, so the existing tri-station network, which can be envisioned as a spider web covering the nation, remains the best tool available for all users of geodetic control, many of whom do not have high precision GPS yet, due primarily to the great investment of money and training time required to make full use of GPS technology. Furthermore, the cost of establishing new stations, equal in precision and value to the existing tri-stations, is very high, and is not born by surveyors, who are in business to make money of course, but passed on to their clients as a part of the cost of completing the particular project, of which setting the new stations is a part. In addition, any markers reset by private surveyors are generally considered by them to be for their use only, since the results of their labor are proprietary in nature, and thus the data pertaining to such reset markers would not typically be available to the public, or even to other surveyors, except through special request, rendering the value of the reset marker very limited. For a reset marker to be of full value to the public, it must be reset by a public agency certified to do such work properly, or a private surveyor working under contract for a government agency, and it must meet the very rigorous requirements set forth for such work by NGS, in which case, again, the high cost of the procedure is not born by the surveyor, but by the taxpaying citizens of the area involved. So in short, every existing tri-station has great value and every one lost is a small tragedy, both historically and economically.

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Rich

Judging from your pictures, I would agree with your conclusion that D 56 has been vandalized. You have positively identified the object setting, the bridge, and verified the exact spot on that object, using the directions and dimensions given in the description, so you have a conclusive result. The difference between yours and the one mentioned by K&S is that in your case the object setting remains intact, although it may have stability issues as you stated. Therefore, many and perhaps most surveyors would consider it damaged but not destroyed, and continue to use the spot, since it is positively identifiable. The NGS, however, which adheres to the strictest interpretation, would consider it destroyed due to the absence of the disk.

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I agree.

 

Although the disk is gone, you can still get a approx. elevation from the setting and most likely be within a CM + or -. While is may not be good enough for precise leveling work it still has value for some applications especially if not other bench mark is nearby.

 

I found one that was set in a RR culvert and the disk was missing, all that was left was a 1" hole in the concrete abutment and the outline of the disk like in the photo above. No other vertical control was close. Since we were doing a hydraulic survey and 1-2 CM accuracy was satisfactory to the hydraulic engineer, we used it (the headwall as the elevation) for the project. btw-Nothing was being built, just mapping all structures up stream/down stream of a new highway bridge.

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Rich -

 

I would agree with both Surveytech and ElCamino on your find for LY1342/D56. Your pictures leave little doubt that the brasscap is gone, however from a surveying standpoint, all may not be lost. If this was a horizontal mark, a surveyor would more than likely just use the drill hole to center on and call it good. Your find, being a vertical mark, is a bit different though. Vertical marks are classified with a vertical order - a rating system to identify the vertical precision of a mark - with First class being highest, and Third class being lowest. Your find was of a Second Class order, per the original data sheet. With this in mind, and the fact that a brasscap is about 1cm thick, a leveling shot on the structure with the drill hole may be accurate enough for many to most applications as ElCamino described.

 

As far as the stability of the setting goes, most man made structures get labeled as 'Mark of questionable or unknown stability'. The surveryors who set the marks were not in the habit of putting them in places that were easily moved and footings for railroad bridges and crossings were/are favorable places to set them. Railroad engineers (civil engineers, not the locomotive engineers) who designed the tracks and bridges overbuilt them to prevent any settling as the trains crossed them. If anything can move a bridge footing or deck, it's a fully loaded, mile long freight train, and they were designed to stay in place for a long time. They make perfect (albeit, sometimes dangerous) places for benchmarks.

 

If I was logging that mark I would not have called it destroyed. I would have posted a note, but that's just me. I wouldn't change your log.

 

WhistlingWind -

 

There is no way I explain the importance of the existing traingulation stations better than SurveyTech so I won't even try. From me, Ditto what he said.

 

GPS is an unbelievable tool for a surveyor, but, even though it's new and hi-tech, and can be accurate and/or precise (more or less), it does not and cannot take the place of proper surveying techniques. 'New tools, Old rules' is something I was taught when I first got into surveying. Much of the work surveyors do is retracing the work of other surveyors, and replacing a station would be doing just that. In order to do it right, it would have to be done in much the same way, even if newer techniques or equipment are employed. Also, even though more precise equipment may be used, the accuracy of the measurement cannot be any greater than that of the original data and/or the original equipment which was used. [For example: a mark that was set 100 years ago with equipment that only measured to the nearest 1/4 of a minute in lat/long cannot be set any better than that, even with modern equipment that can measure to the 1/1000 of a second of lat/long. Precision and accuracy have not increased, only the probability of error.]

 

With all that (long-winded stuff) being said, GPS does make it possible to measure to a known or relocated point much more accurately than ever before, and with much more precision than what has been attainable. ...and it is so much easier.

 

Keep on Caching!

- Kewaneh

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