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pgrig

Scaled Marks: Why Do We Bother With Them?

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As I start out on my 2nd year of the GBQ (Great Benchmarking Quest), I was planning a few Scaled marks for an early trip when this question hit me: "Why do we bother with these suckers at all?"

 

Here on GC.com we engage in lengthy discussions (which have helped me a lot!) on whether to accept this or that Adjusted mark as Found or Not Found, based on complicated assumptions concerning their precise history, placement, and stability, or lack of same--usually accompanied by arguments that the slightest displacement (or mis-location) of these marks over time renders them useless for practical purposes.

 

But the NGS database contains (and we hunt) Scaled marks that have no practical location whatsoever, often turning up many hundreds of feet distant from their (admittedly imprecise) officially designated positions.

 

I suddenly realized that I don't understand why Scaled marks are even carried in the NGS database at all, or have any practical utility. Are they in fact marks that were initially set with precise locations but for which precise location data were lost in the mists of time? [i believe that I know that Scaled marks are useful primarily for their elevations, but how useful can this be if we don't know precisely where they are on the ground?]

 

Would one of you Great Ones please enlighten me? :-)

 

Many thanks,

-Paul

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Marks in the data base serve two purposes: marking an elevation and marking a horizontal position (lat-lon). If it is SCALED for one or the other, that value is only useful for finding its general location.

 

But nearly all entries in the data base have either an ADJUSTED elevation or an ADJUSTED horizontal position or GPS OBS value. Many (especially newer ones) have both. I don't recall seeing any that had neither.

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pgrig -

 

We, as hunters, think of the marks as scaled because it has implications about searching with a GPS. However, to the people who wanted these marks established, they are thought of as vertical control. Vertical control is used in construction of roads, railroads, buildings, dams, water and sewer systems, etc. Railroads, for example, need to assure that they have (and maintain) minimal loss of energy.

 

The NGS has some articles on this.

 

Here are their introductory articles on leveling.

 

This one speaks of the HtMod project - using GPS to increase height accuracy.

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Scaled horizonal marks were set by the USGS in their work doing the great Topo maps that we use to find those scaled marks. Ever notice how many marks are shown on the Topo maps that are not in the NGS database? Someone had to know where they were located in order to put the "X" on the map showing where they are.

 

Local surveyors use them to insure that water and sewage flow the correct direction and distance (it flows down hill!).

 

Beside, it adds to the enjoyment of the hunt when you don't have adjusted coordinates.

 

John

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Leveling runs establish precise elevations, but the process very rarely includes precise horizontal location. The surveyors used maps to locate the marks after they were set. All that's necessary for an elevation mark is a pretty good idea about how to find it. When it is used as the basis for elevations on a project, the project itself will be horizontally located by other means, when necessary. All this, though, suggests that it really can be helpful for us to submit handheld coordinates for scaled marks.

 

As to the usefulness of marks in poor condition: a horizontal control mark may have some usefulness left in it if the center of the stem can be located. But if you come on a broken stem of an elevation mark, there is no way to usefully estimate the distance from the present stub to the top of the absent disk. Establishing elevations from existing marks involves use of more than one bench mark as a check, and as material for adjustment, so the slightest discrepancy in a vertical mark can cause trouble.

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Beside, it adds to the enjoyment of the hunt when you don't have adjusted coordinates.

 

John

 

LOL. Now who's going to wipe the wine off my keyboard?!?

 

I usually check the topo maps to look for the little Xs showing where the scaled marks are. Then I get the coords from the topo map. Oddly, last week I found two (in the same series) where the Xs were over a hundred feet off. That surprised me!

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Simple answer:

 

The "Scaled Marks" you are talking about are very, very accurate in elevation, but not in position.

 

The "Adjusted Marks" you are talking about are very, very accurate in position, but not in elevation.

 

Very rarely you will find marks that are accurate in both elevation & position. These are becoming more common with the advent of GPS.

 

P.S. It took me a while (some years ago) to wrap my head around the differences. Don't feel alone.

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And I have a little 'attitude' issue. In reality a benchmark is a vertical control point. All those evil 'scaled' points are the REAL benchmarks.

 

What this forum and it's users do is recover and help more precisely locate those things which are used to determine the elevation of things that have a major impact on a lot of infrastructure and things like gettin water to run downhill in a pipe that is uphill because someone didn't check into one of these stupid obsolete markers. Finding these things is a service to NGS and society in general. So don't worry about them?

 

To me given a station with an adjusted coordinate, what is the dadgum challenge. That is like shooting ducks in a bathtub. We already know where they are precisely. And much more precisely than YOU can provide any update to. Now it is useful for NGS to know if these still EXIST or if there is a chance they have been disturbed or destroyed. But that info is not as useful as knowing the same about a 'benchmark', and knowing also where it is more precisely which is a function that the people here can provide.

 

So go ahead and shoot all the ducks in your bathtub, but don't try to claim you are a great hunter at the same time.

 

No one discusses this here much but a benchmark is a vertical control point, most often not having a precise horizontal position. The horizontal marks that are "adjusted" are part of the horizontal control network and are not technically benchmarks. You guys have munged the two together, but every once in a while maybe you need to be reminded about the correct definitions.

 

Just because the 'station' is in the benchmarking database does not actually mean it is a benchmark by the traditional surveyor's definition.

 

This would not be an issue with me if someone didn't come up with an attitude about why bother recovering these unadjusted points!! Well sorry they are the actual true benchmarks and the adjusted ones are not. And while it does take some skill and effort to recover 'adjusted marks', they are not benchmarks. Sorry!

 

- jlw

Edited by jwahl

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pgrig - About a year ago I was wondering if we could use a strategy of recovering stations that had the highest “value” in the database, rather than whatever we felt like recovering, so I contacted our NGS Geodetic Advisor to Arizona and asked if he had an opinion which Stations have the highest priority for recoveries in our area. He said: “…I have no priority areas to recommend. However, with the advent of GPS horizontal control stations are not nearly as "valuable" as they used to be. On the other hand, vertical control marks (i.e. benchmarks) are more valuable than they used to be since we pretty much stopped leveling in the mid-80s. So, if all other things are even I'd suggest you look for benchmarks rather than triangulation stations. But if you like to climb you'll find the tri stations are on top of hills/mountains and the view is probably better…”

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Vernacular is a problem. A while ago, I believe it was ArtMan who suggested using two terms: "benchmark" and "bench mark". The first one, one word, refers to the things we look for here in the Benchmark Hunting section of the Geocaching site. The terms are defined here in the Benchmark Hunting FAQ page.

 

Perhaps it's a bad convention, but at least it follows the generalized concept of "Benchmark Hunting". Certainly what is written on the disks is "Bench Mark", a more specific term for vertical control points. Perhaps a different convention would be "Station"s and "Bench Mark"s. But then, there's no word for both, except "control points", and then the FAQ would need to say something like "In the Benchmark Hunting section, we look for Control Points." That might begin to frustrate people even more. We also look for azimuth marks, reference marks, and witness marks. Those aren't even control points, unless I'm mistaken. What to call them all? Benchmarks? Marks? Markers? Stuff in the NGS database? PIDs?

 

Certainly if a better convention could be devised, the FAQ could be fixed in a subsequent edit by volunteers. There would still need to be some kind of verbal bridge to define the term "Benchmark Hunting" that the Site uses. We (the volunteers of the time) settled on the "benchmark" vs. "bench mark" convention last time.

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BDT is right, we are a little stuck with what we have. As he said, there were some long threads several years ago, discussing pros & cons in painful detail. In trying to walk a middle line & simplify (especially for relative new comers), I sometime use "mark" as a generic term (see my post above). Could be a Bench Mark, or could be a Station Mark. Or, even reference Mark or Azimuth Mark. Works, doesn't it?

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I'm not sure why this thread reminded me but ... my first trip out to hunt marks for the contest, I chose a route to a part of the county I hadn't been to in a while and happened to have a lot of benchmarks along the way. I had all the PID's listed and didn't realize it till I got back to log them that many of them were part of a series, the last three digits of the station name/designation were the same and the the first digits were letters in a sequence. I thought that was pretty cool - traveling the same route the survey team did. I looked and there are a few others of the series close by but some letters are missing and i was surprised to find a couple far away - say 50-100 miles.

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In my own logs and forum posts I avoid the generic word "benchmark" altogether, I call them survey markers.

 

If there is occasion to be more particular, I'll call them "Triangulation Stations", "Reference Marks", "Bench Marks", "Traverse Stations", "Magnetic Station", etc.

 

I assume no one notices the distinctions I make, since ordinarily I wouldn't draw attention to them, but I do it for myself.

 

Two side issues that make life a little more interesting:

 

1) The USGS has for years used the same kind of disks for both vertical and horizontal control stations. Like the one pictured above, these disks have a triangle in the middle (Triangulation Station?) and the word "Bench Mark" at the bottom (Bench Mark?) . Which is it? Could be either. read the data sheet. I guess they wanted to save money on disk manufacture. The USC&GS, OTOH, made a gazillion kinds of disks with a great variety of stampings.

 

2) Not just us folks, but hikers and mountain climbers typically call the disk found on many mountain tops "The Bench Mark" when these are almost always triangulation stations. I guess some of them are USGS disks, so who can blame them. They also often assume these disks mark the high point of a mountain, when often times they don't.

 

BTW: is "data sheet" one or two words? Datasheet? :laughing:

Edited by Papa-Bear-NYC

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Why SCALED marks? Because marks with ADJUSTED horizontal coordinates are too easy. Finding a mark with SCALED coordinates is just over three times more satisfying than finding one with ADJUSTED horizontal coordinates.

 

"Datasheet" is, when used in the context of hunting for (attempting to "recover") a monumented (set in place and documented for inclusion in a database) benchmark (be it a bench mark, triangulation station, tidal station, or whatever name you wish to give), a term of art rendered as a single word (like they do on the NGS web site). Or is it "website"?

 

Will

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I use the same procedure as PapaBear - I don't use the word "benchmark" in my postings. When I'm referring to a point with an accurate elevation I use "vertical control point". For a generic term I use "survey mark"

 

VERTCON is a program (software) that converts NGVD 29 elevations into NAVD 88 elevations, see: http://www.ngs.noaa.gov/TOOLS/Vertcon/vertcon.html

 

Regarding the challenge of finding marks, I would propose that mark hunters try finding even adjusted horizontal marks without using their GPSr. That's the way all surveyors did it until a very few years ago. Reading the description (and all the recovery notes) is very important and is often the difference between finding a mark and not finding it.

 

As far as value of recovery, the AZ NGS Advisor, Dave Minkel, is correct, vertical control points are more valuable today.

 

GeorgeL

NGS

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As to whether to say "datasheet" or "data sheet," notice that the NGS retrieval page and most of not all of its sub-pages use the one-word form. When you complete a retrieval, it is headed thus:

 

The NGS Data Sheet

 

See file dsdata.txt for more information about the datasheet.

 

So we remain uncommitted.

 

Cheers,

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Finding a mark with SCALED coordinates is just over three times more satisfying than finding one with ADJUSTED horizontal coordinates will.

 

Finding all parts of a tri station makes it interesting. 50 or 75 year old azimuth marks can be dauntingin some cases.

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t8r

 

You are correct, sir. Finding all the parts of a tri-station is very satisfying, and the AZ part is especially so. Few AZ's have their own PIDs, and those without PIDs are (usually) less well-described than marks with their own datasheets. They are, for most intents and benchmark hunting purposes, just like marks with SCALED coordinates.

 

The tri-station, itself, is fairly easy to find if you have a clear sky. The RMs are not much more difficult because you can (well, I often do) use FORWARD to calculate a position that is alomost as good as ADJUSTED. But the AZ is is as good as a bench mark disk.

 

Will

Edited by seventhings

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VERTCON is a program (software) that converts NGVD 29 elevations into NAVD 88 elevations

George, are you saying that the term used on datasheets is named after a software program? Such as on the datasheet for the mark that John and Shirley showed in their posting, HN0794?

 

Patty

Edited by Wintertime

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Hi Patty:

I believe that is correct. Read down about 8 more lines:

 

HN0794.The NAVD 88 height was computed by applying the VERTCON shift value to
HN0794.the NGVD 29 height (displayed under SUPERSEDED SURVEY CONTROL.)

 

So, I believe the VERTCON software was used to convert the mark elevation from the older NGVD29 vertical datum to the newer NAVD88 vertical datum.

 

That has been my interpretation of this datasheet entry previously. But if I'm not right, someone else will jump in here, I'm sure.

 

Klem

Edited by Klemmer & TeddyBearMama

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Leveling runs establish precise elevations, but the process very rarely includes precise horizontal location. The surveyors used maps to locate the marks after they were set. All that's necessary for an elevation mark is a pretty good idea about how to find it. When it is used as the basis for elevations on a project, the project itself will be horizontally located by other means, when necessary. All this, though, suggests that it really can be helpful for us to submit handheld coordinates for scaled marks.

 

 

__________________

 

I find this thread very interesting!

 

The quote above by m&h actually hits the crux of my initial question, which, boiled down, asked, "How can a mark be useful if we don't know where (horizontally) it is? And my concerns were heightened (good pun, huh?) by the fact that most of the scaled marks I have hunted have had really sloppy directions, so sloppy as to render many of them virtually unrecoverable.

 

It often takes me hours for one of these, or a hunt equivalent to finding (and documenting) a tri-station with three "copper pin in lead" RMs which have neither direction nor distance described on the Datasheet (from the website :D . By the way, is this phenomenon, the reporting of "cloaked" reference marks, characteristic of Mass., or do others of you get to experience the joy of hunting these down? [see, for example, MY2758.]

 

I was not trying to somehow demean the scaled mark, or to give it some sort of second class citizenship, and it's interesting to see that many folks consider recoveries of these to be more valuable than recoveries of tri-stations. And I only resort to "shooting a few ducks in the bathtub" (which to me means going after roadside stations set by the Mass. Geodetic Survey in the 1970s) when I've emptied both barrels at a particularly stubborn scaled mark with no success. :D

 

By the way, is it proper to call a scaled bench mark a "station"?

 

Thanks for all the interesting comments!

-Paul

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Paul, Vertical Control Points (VCP) are extremely useful. I agree that their descriptions are often poor and their horizontal positions are often poor (scaled from a map). The level crews often leveled along a railroad line and just kept rough track of how many miles they had progressed along the rail line. They didn’t travel to each VCP point using the nearest road so they didn’t have the opportunity to draft the normal “To Reach” that we are so familiar with for Horizontal Control Points (HCP). The horizontal positions of VCP are poor because the level crews had no means to get accurate horizontal positions.

 

In this day and age of survey grade GPS, it is quite easy to obtain a very accurate horizontal position, but GPS still does not yield the same quality of vertical accuracy as old-fashioned spirit leveling. So, the VCP points are useful because they provide accurate elevations, assuming of course that they haven’t moved since originally surveyed. (Notice I didn’t use the term “bench mark” anywhere above.)

 

In answer to your question, -is it proper to call a VCP a ‘station’-, see the definition below.

 

From NGS’ GEODETIC GLOSSARY (which is not on-line):

 

station - (1) A physical location or site at which, from which, or to which observations have been made.(2) A point representing the physical location or site at which, from which, or to which observations have been made. The principal kinds of station, named for the kind of observations made there, are: air station, gravity station, magnetic station, survey station (including bench marks and triangulation stations), and tide gauge or tidal station. Stations are also classified according to their order of importance: base station, principal station, supplementary station, etc.

 

But, in common usage that I have heard, the word “station” is most often used when referring to a horizontal control point.

*****

Patty – yes, the VERTCON software was used to convert from NGVD 29 to NAVD 88. It is not as accurate as new, adjusted leveling data, but good to about 2 cm.

 

GeorgeL

NGS

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"By the way, is this phenomenon, the reporting of "cloaked" reference marks, characteristic of Mass., or do others of you get to experience the joy of hunting these down? [see, for example, MY2758.]"

 

Paul, we posted an inquiry about this problem a day or two ago, and have not had a reply yet. The case of MY2758 is not as blank as some. The recovery paragraphs give that vague description of the RMs being about fifty feet from the mark and about 120 degrees apart. The "box score" higher up in the datasheet gives the directions to the three marks. It's imprecise, but better than nothing. The "box score" usually also gives the metric distances, but not here. Challenging, eh?

 

Cheers,

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m&h--

 

In the last couple of trips, I've had several of these SOTR (Somewhere Over the Rainbow) reference mark sets, and I'm developing the knack of finding them, as with this site, which I'll log soon.

 

By the way, are you local to me?

-Paul

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Paul--

 

We started mark hunting in Maine and Nantucket, but we've lived in Washington state for the past several years. We've enjoyed your sagas.

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Here is an adjusted one that will be hard to match for accuracy with HH2, or survey grade GPS, for that matter. How did those guys do that? MEL

 

PX0470 DESIGNATION - PILOT PEAK

PX0470 PID - PX0470

PX0470 STATE/COUNTY- WY/PARK

PX0470 USGS QUAD - PILOT PEAK (1991)

PX0470

PX0470 *CURRENT SURVEY CONTROL

PX0470 ___________________________________________________________________

PX0470* NAD 83(1993)- 44 58 34.34358(N) 109 52 53.14214(W) ADJUSTED

PX0470* NAVD 88 - **(meters) **(feet)

PX0470 ___________________________________________________________________

PX0470 LAPLACE CORR- -7.40 (seconds) DEFLEC99

PX0470 GEOID HEIGHT- -7.51 (meters) GEOID03

PX0470 HORZ ORDER - THIRD

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Here is an adjusted one that will be hard to match for accuracy with HH2, or survey grade GPS, for that matter. How did those guys do that? MEL

 

PX0470 DESIGNATION - PILOT PEAK

PX0470 PID - PX0470

PX0470 STATE/COUNTY- WY/PARK

PX0470 USGS QUAD - PILOT PEAK (1991)

PX0470

PX0470 *CURRENT SURVEY CONTROL

PX0470 ___________________________________________________________________

PX0470* NAD 83(1993)- 44 58 34.34358(N) 109 52 53.14214(W) ADJUSTED

PX0470* NAVD 88 - **(meters) **(feet)

PX0470 ___________________________________________________________________

PX0470 LAPLACE CORR- -7.40 (seconds) DEFLEC99

PX0470 GEOID HEIGHT- -7.51 (meters) GEOID03

PX0470 HORZ ORDER - THIRD

 

Pilot Peak is an intersection station which can be seen (and triangulated to) from many tri-stations in the area including Trout Peak. I took this picture in 1983 while surveying for seismic oil exploration.

 

c5dc1c3d-a04f-4b23-b55b-13ec36a14618.jpg

 

Pilot Peak can just barely be seen on the far horizon.

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This may be obvious to all you seasoned geocachers, but I've read somewhere that SCALED benchmarks are so off because their calculated by someone in an office with rulers, pencil, and a map. I believe this is actually on geocaching.com. But just wanted to through that out there.

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True, well the database was compiled from paper records someone had to determine many of the points from reading the description and plotting it on a USGS quad map. Most of the field operations produced maps with the mark sketched on them but searching thru all those records was time consuming.

 

Searching and updating those mark with GPS coords is part of the challenge.

Edited by Z15

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And because in many cases the conversion from map to coordinates was done many years after the descriptions were written, there are occasional gross errors. I know of two cases where a highway route number was moved to different roads a few miles away and the coordinates are on the NEW road instead of where the route was in 1934.

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This may be obvious to all you seasoned geocachers, but I've read somewhere that SCALED benchmarks are so off because their calculated by someone in an office with rulers, pencil, and a map. I believe this is actually on geocaching.com. But just wanted to through that out there.

 

Basically correct, but as most of us know, the scaling was done by NGS employees many years (most of the marks anyway) before Geocaching.com or even GPS were ever though of.

 

As an aside, I find I can often predict the accuracy of the scaling based on the era of monumentation.

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