The Downside of Benchmark Hunting

I saw that a couple of days ago. It's very frustrating, and if you contact the seller they will must likely just get angry.

We've debated this here before and unfortunately I am waiting for someone to state once again that the old bench marks are no longer needed because of the use of GPS. Yes, someone here did argue that. Sad...

I'll bite

The use of old benchmarks is not as necessary with GPS. However, I do like to use the more recent and not as pretty brass rod in aluminum casing. You think we could sell one of those on eBay?

Sorry the future is coming fast and passive control is finding it's way into the history books.

My message to the seller:
"Found" probably translates as "pried out of a rock" where it was set by a US Govt agency. It is illegal to disturb these, and should and may be illegal to sell them. Please remove this listing so as to not encourage others to break the law.
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To eBay: "Report Item"
Prohibited and Restricted Items
Government and Police Related Items
Other Government and Police Items
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There may be other categories you could use to harass eBay into paying attention to these.

Save our Benchmarks!

GPS on Benchmarks is a vital part of developing the GEOID Model. If all the Benchmarks are pried out and sold on EBAY we can't develop an accurate GEOID Model.

It's very sad, GPS is very crude with respect to e. Only by trying to warping the crude GPS value to the sophisticated values represented by the bench system has GPS even been able to come close to a useful realization.

Of course, GPS is still not there when compared to the Bench System. Clearly we still need to have this resource, so much is built from it.

Over time CORS/Geoid/OPUS drifts and bounces along while the passive network particularly with respect to e offers a much more stable network. Losing it is not a good thing at all.:-(

Reply from seller:
You are wrong. Found means it was sitting on it s side on the ground in the desert sticking about half way out of the dirt many decades ago.

It would be nice if we could find Surveyor who used this point within the last few months and can say he found it attached to something not just found on its side.

I'll bite

How do you prove your GPS is set up correctly? Oh yea by using a published monument.

I am sure in the future we may not need gas stations, but that doesnt mean we should start to tear them all down today.

With the recent huge increase in membership of NSPS they may have some weight in this matter. Maybe someone can get them - and a lawyer or lobbyist to start working on EBay.

I doubt this particular mark was of any importance, perhaps never being used after the initial mapping data was taken. I searched a little (not exhaustively) and found several with this designation in the NGS data base, but not this particular disk. So many of the USGS disks were not measured to the standards needed for inclusion in the NGS list.

But I still don't like seeing them on ebay.

I'll bite

Benchmarks used to produce local information are a critical part of that legacy data. Your GPS can improve to trillionth of a foot accuracy and it will have zero value without that connection. Removal of benchmarks for profit should be a felony.

FWIW,

I recognize the appeal of those marks in the ground. They represent a tangible link to a height system. Unfortunately, their reliability is questionable. While we might assert that within the parts of the "stable" North American plate BMs are unaffected by tectonics, there are multiple sources of disturbance.

Having worked in 49 of the 50 states, I have seen the decimation of the vertical network. As I never had the luxury of basing my surveys on one benchmark, I frequently found discrepancies when attempting to verify the published heights. Without these checks how can one say that their favorite monument is correct?

Leveling to national standards is an expensive proposition. Releveling the national network is NEVER going to happen again. In fact, if you read about the NAVD88 project you will see that this last leveling was much limited in scope and some methods allowed due to budgetary considerations.

I cannot resist quoting from the Heiskanen and Mortiz text "Physical Geodesy" : "Leveling without gravity measurements, although applied in practice, is meaningless from a rigorous point of view..."

NAVD88 network has also been found to be deficient with improved knowledge of the gravity field which revealed a systematic tilt from the SE to NW. For an excellent discussion of the relevant issues see the NGS White Paper: http://www.ngs.noaa.gov/2010Summit/Improving_the_NSRS.pdf

The Canadians have already adopted a new height system based in GPS-derived ellipsoid heights plus a geoid model. The U.S. is following the same path.

Does this mean that the loss of monuments is without consequences? Of course not. At a minimum I would hope that he NGS, the lead agency on these issues, would provide a tool like VERTCON to allow the use of legacy height systems.

As we have all seen over the last decades, good quality ellipsoid heights can be obtained. We have also seen improvements in geoid models. Users should also know that the models with GEOID in their names are hybrid models. They are created after the gravimetric model, are based on it, and include a fitting procedure to account for measurements of ellipsoid heights on points with published NAVD88 heights.

BTW, I recollect folks at NGS HQ contacting eBay on this issue multiple times. Yet it continues. While there is the "$250 Fine" note on the disks, I doubt it has ever been collected. In addition to disks wrenched from monuments there are many defaced disks and disks showing evidence of unsuccessful attempts at removal.

In closing, my favorite anecdote on this matter was a discussion with an irate landowner who was disturbed that I chipped the disk out of a monument (benchmark) that had been pulled from the ground by a snow plow. He told me if he knew what I was going to do he would have out it back in its hole.

Cheers,

DMM

In a perfect world the email I sent to the the NOAA director would prompt them to fine both the seller and buyer.

I also reported it to EBay as noted above.

Maybe a couple hundred phone calls might do some good too.

>I am on leave today, May 22. If you need immediate assistance, please call >301-713-3222.

>Thank you,

>Juliana

>Juliana P. Blackwell
>Director
>NOAA, National Geodetic Survey
>1315 East West Highway, N/NGS
>Silver Spring, MD 20910
>www.geodesy.noaa.gov