Jump to content

No Benchmark Disk, Found A Stem


bicknell
Followers 0

Recommended Posts

I double checked the FAQ and even did some quick searches, but I can't find a solid answer. So, I want to post a make sure this is clear, and request this go in the FAQ.

 

I found two marks today where the disk was gone, but the setting and stem were intact and the outline of the disk was still visable. It's my understanding that if the mark is a triangulation station (or other horizontal mark) that this would be POOR/DISTURBED, as the horizontal position is still good, and that if the mark is a benchmark (or other verticle mark) this would be NOT FOUND, as it can't be destroyed without the disk, and it's useless for height since with the disk missing the height has changed.

 

Please confirm I'm correct, or, well, correct me. :angry:

Link to comment

fyi

 

Q: I am submitting a recovery report and I want to know what is the official, exactly, legal, 100% accurate definitions of “good”, “poor”, “not found” and “destroyed”?

 

A: There are no official definitions. I am sorry, but you will have to actually use your own judgment here. Destroyed marks are handled separately and should not be submitted through the mark recovery page. Destroyed marks are handled by emailing Deb.brown@noaa.gov

 

Here are some guidelines used by NGS employees to describe the condition of a mark:

 

GOOD -- Recovered as described on the datasheet; looks healthy and happy.

 

POOR -- Recovered, but shows some alarming evidence of damage or movement. Often the marks can get run over, or frost heaved, or the ground is just too soft to support it. If the mark is scarred and leaning (i.e. the victim of a tractor-lawnmower), thrust up from the ground like a mushroom and/or surrounded by tractor ruts, it's poor. If the disk is gone but some evidence (stem) remains, then it could still be useful; that's a POOR too. Please describe the problem you see in the notes section of the report.

 

NOT FOUND -- I can't find it. Describe how hard you looked or confused you were, e.g., "not found after 10 minute search; unable to recover because all witnesses are destroyed" or "not found; existence doubtful, entire area is now a new shopping mall."

 

DESTROYED -- We prefer the more optimistic "NOT FOUND" unless you have direct first-hand evidence that the mark is completely obliterated. Getting a mark listed as destroyed requires submission of evidence (like a photo) and an e-mail.

 

 

it's useless for height since with the disk missing the height has changed.
Even if the disk is gone, the height may still have some use as not all survey work often requies a precise elevation. I can think of several projects in which we wished we had a rough elevation to come from to check drainage or some other feature. Edited by Z15
Link to comment

bicknell -

 

I would have agreed, but it seems that Deb is (sometimes?) recommending POOR even for benchmarks with missing disks. Here is a report of a find of a horizontally SCALED mark, JE0768, and a quote by Deb saying

"Let's play this one safe and log it POOR with text that explains that the setting is intact but raised and the disk is missing."

 

I'm beginning to feel that Deb would actually like to be emailed on all of these severely damaged marks to assist in the determination of report classification instead of a rule or set of rules being used by us. I don't know. It seems like a lot of email work, but perhaps to the NGS it's worth it to get the best possible decision on mark grading.

Link to comment

Ok, to add some detail, here's the marks in question. So far only in geocaching.com, as that's easier to change.

 

JW0193

 

JW0197

 

It does seem POOR might be better for both of these. With the rest of the setting intact, it seems safe to assume the normal disk thickness (1-2cm?) is what is missing, and these are clearly the points (stem, disk outline).

 

I'll wait for a few more posts, and if necessary send e-mail to Deb tomorrow.

Edited by bicknell
Link to comment

Agreed; POOR for both.

 

If you email Deb, you might consider asking her something like:

 

For all such findings where the disk is gone but the shank and disk-scar remains do you prefer that we (at GEOCAC) label them all POOR whether or not they are horizontally SCALED or ADJUSTED, or would you prefer that we emailed you with a picture about each one to make the decision about the grading on a case-by-case basis?

 

It's interesting that one of the marks was graded POOR by the NGS. I wonder if it had no cap back then. One would think that saying that the cap was gone would be critical (required) information to report. I have wondered in the past about recommending to the NGS that they include a radio button on thier recovery page for "cap pried off".

Link to comment

To use a Bench Mark for vertical control, I must rest a level rod or Prism pole upon the top of the disc to measure the elevation. That very point is the elevation on the datasheet. If the disc itself is gone, or altered somehow, the elevation it was said to have is gone. The rule is I cannot use it to tie in if the numbers do not concur.

 

I consider the the elevation gone, Not found. I submit them as such and it is my call. This is what my training and experience tells me. I found the station monument, or what is left, Sure, but the station's data quality is gone, and that is what i need. I cannot destroy it, so this is my way of saying there is nothing here that can be used to the next guy, and I note why. This only holds true for vertical control.

 

If it is triangulation, It is a different deal. I do not have to physically touch the Disc for my measurements, though I can. I am merely aiming for the center. I can use it's center if the disc is missing, so I consider it Poor, but certainly still usable.

 

Feel free to ask Deb if you like, But I work the field and that is how I call them. I am also Basing this from what is required of me given the engineering spec I am following at the time. Most often than not, I can't use data which I cannot derive, and compare.

 

Rob

Link to comment
To use a Bench Mark for vertical control, I must rest a level rod or Prism pole upon the top of the disc to measure the elevation. That very point is the elevation on the datasheet. If the disc itself is gone, or altered somehow, the elevation it was said to have is gone. The rule is I cannot use it to tie in if the numbers do not concur.

 

If it is triangulation, It is a different deal. I do not have to physically touch the Disc for my measurements, though I can. I am merely aiming for the center. I can use it's center if the disc is missing, so I consider it Poor, but certainly still usable. [snipped slightly for brevity.]

 

There is nothing better than getting educated by the end users--the guys and gals who actually use these disks! Thanks, Rob! This is a helpful perspective for those of us who are "monument dusters".

 

-Paul-

 

They say that experience is the best teacher. But they're wrong. It's too expensive. Someone ELSE'S experience is the best teacher!

Link to comment

It did seem a bit odd to me that a benchmark (the real definition; vertical control) would be labeled as condition POOR even though it would seem logically unusable when the disk part of the monument is gone. However, we must all remember that it is the NGS's database and Deb is their spokesperson for it.

 

I'm thinking that the problem is that there needs to be 1 or 2 more labels somewhere between POOR, NOT-FOUND, and DESTROYED (via NGS deciding it's DESTROYED). We're non-survey-professionals (most of us) and perhaps the NGS is leary of a lot of DESTROYED PIDs resulting from our investigations, even if the NGS is the one making the final decision on each one based on our evidence. With only those 3 choices available for significantly damaged marks, a label of POOR at least gives the clear idea that something's out there still, and a verbal recovery note saying that the disk is gone should be enough for surveyors to evaluate whether or not it is within their specs to use it even if the liklihood of that is essentially zero. Therefore the verbal part of the recovery note fills in the labels-gap of what the exact condition is.

 

Hopefully Deb will clear this up further for us somehow. Perhaps her answer is to work it through her on a case-by-case basis during the recovery submission process rather than for us to try to use a set of rules.

Link to comment
It did seem a bit odd to me that a benchmark (the real definition; vertical control) would be labeled as condition POOR even though it would seem logically unusable when the disk part of the monument is gone. However, we must all remember that it is the NGS's database and Deb is their spokesperson for it.

http://gpsinformation.net/main/ngs-accuracy.html

 

Both of the marks in question are Second Order Class 0 per the data sheet. Based on the link above, which doesn't have that particular description, I think that would make them between +-10cm, and +-20cm accuracy. I figure the disk is 2cm thick, at best.

 

So, it seems to me if a surveyor goes to the mark to check some other point, and gets +4 cm from what he was expecting to the stem, adds 2cm for the missing disk, +6cm, and considers a 2cm margin of error cuz the disk is missing (so +4, to +8cm), he's still within the 10cm accuracy.

 

I'm sure I've just oversimplified way too much.

 

It may also be the NGS would rather downgrade it to third order and continue to use the mark than make it completely worthless. *shrug* Not every mark is an A-Order triangulation station tied into 20 other marks and accurate to 0.5cm. I'm sure a surveyor would avoid a broken disk if given the choice, but if for some reason they didn't have a choice, or for instance if being within 10cm was good enough the broken disk may make a great spot.

 

That's just my random thinking though.

Link to comment

bicknell -

 

Interesting points!

 

By the way, here is the NGS tables of Vertical accuracy of the different levels of Orders and Classes (once again with no class zero, but presumably near to the other second order values). Down to Fifth Order, the standar error of measurement, even for marks within a KM of each other is up to 6cm. Possibly never used for anything, but it IS included in the table.

Link to comment
I'm thinking that the problem is that there needs to be 1 or 2 more labels somewhere between POOR, NOT-FOUND, and DESTROYED (via NGS deciding it's DESTROYED).

 

Occasionally, there is a notation: SEE DESCRIPTION.

 

Casey, is this something that went away?

I'd love to have a SEE NOTE option.

 

-Paul-

Link to comment

I am not sure I understand what you mean, but I'll try anyways.

 

You can always include notes in your recovery. When somebody puts these recoveries into the database they can put something on the datasheet that says "see recovery note" or whatever. But non NGS people don't have that option and I dont think they ever did.

 

-Casey-

Link to comment

Hi, Casey:

 

The times when I have seen this, it has been submitted by an agency such as NGS or NCGS. Once it was attached to a USPSQD report, but that might have been entered by NGS on their behalf.

 

I have not seen it on any recent reports. When I run across it again, I'll post some samples.

 

Regards,

-Paul-

Link to comment

Bicknell,

 

You said:

 

>It may also be the NGS would rather downgrade it to third order and continue to use the mark than make it completely worthless. *shrug* Not every mark is an A-Order triangulation station tied into 20 other marks and accurate to 0.5cm. I'm sure a surveyor would avoid a broken disk if given the choice, but if for some reason they didn't have a choice, or for instance if being within 10cm was good enough the broken disk may make a great spot.

 

The truth is, We have a choice. And we cannot use the altered station as a choice for Bench Mark tie ins. If these stations are found in the wild to be altered, especially for vertical work, it is considered good practice to pass on them. (we cannot build a drawbridge over a critical waterway as based on by guess and by golly.) They are not downgraded in accuracy. They have zero accuracy, because we have no idea what has happened... It is not something we attempt to surmize, second guess, call good enough for government work, or grade on a curve. We don't bump them up or down, they are predetermined to be surveyed in, to a given accuracy. It is something done as per plan. The plan is to follow the plan, If the Plan is not working, go find another station and follow the plan.

 

Accuracy is granted on the basis of a given number of observations and least squares adjustments. It is a methodology which is rigorous and adhered to. Once the station is altered from it's original accuracy, all this has to be re-accomplished, and the "order of accuracy" is now No accuracy at all. Accuracy is granted on the basis of how many concurring observations were made on the station, and in some cases such as a baseline the stations may be observed from more than one Path of leveling.

 

Because of the alteration they will not concur with the Datasheet, and we cannot legally use them as tie in's for certified survey work.

 

It happens, and this is why in some cases you see reset stations. That is a station to replace the damaged or missing station and it's data can be certified accurate. If we could use damaged or altered survey markers, there would never be a need to reset them.

 

HTH

 

Rob

Link to comment

Well, I got e-mail back from Deb. She said POOR/DISTURBED for both noting that the disk is missing and the stem is intact and can be found in the description. So, it appears POOR/DISTURBED is for benchmarks too when the stem is still there.

 

Well, at least it's two more finds for my count. :unsure:

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Followers 0
×
×
  • Create New...