m&h
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Posts posted by m&h
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We would add to Bill93's excellent note that the adjustment itself is usually a much later process than the one he describes so well.
Having obtained coordinates by those classical methods, and having a certain number of calculations for the same point, all of them different by tiny distances (usually!), a mathematical procedure called a least squares adjustment can be run on the set, and the result will be the most likely set of coordinates, carried out to five decimal places. Least squares procedures come out of statistics and probability. They work best when the set of quantities to be adjusted is fairly sizeable.
Datasheets bearing adjusted coordinates usually have a line saying when the adjustment was made--early 1990s in many cases. But usually the sets of coordinates for the point were gathered long before--often decades back.
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Could be tough, could be very worthwhile.
The buried mark is the permanent mark, and should not be disturbed by any person not employed or assigned to the task by NGS. The surface mark is directly above the buried mark, and except in extraordinary circumstances, the surface mark is the one everybody uses. A witness post is a visible marker, made these days of fiberglass but in those days of steel fence-post stock, slender and three or four feet high, bearing a small sign announcing the presence of a survey marker. In the relentless disintegration process, the witness post is usually the first thing to go.
Triangulation stations are among those marks that are equipped with reference marks; that's probably what you have here. The purpose of the reference marks is to provide a means of replacing the primary mark, if it is lost and the reference marks remain.
We haven't got quite enough information to be more precise here, but we would suggest narrowing down the GPS reading as much as you can, perhaps by setting it on a tripod and turning on the AVG function for twenty or thirty minutes, and then going to work with a sharp eye or a metal detector or both.
Good hunting!
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The oldest station we can claim is Sankaty Head Lighthouse, UT0553, first observed 1867. There's a drill hole (PE0892) in Camden, Maine that we are fond of thinking might be older, but its monumentation is UNK and it was finally first described in 1962.
Not quite as old, but more fun for us, were a couple on Nantucket that hadn't been reported to NGS since their monumentation. LW4252 was set in 1887, and soon thereafter, we would guess, broken off just below ground level. Its companion marks, LW4184 and LW4151, were reported to NGS in 1909 and 1955 respectively, and it was known that there were three of them. So the south stone's near-destruction must have been pretty early.
LW4246 is a much sounder stone that was set in 1887.
One that has often been logged here but rarely at NGS is SY2718, in Tacoma. At NGS, set in 1892, found good in 1905 and 2006.
Cheers,
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The benchmark database at Geocaching.com cannot be edited or added to. If you find a mark that isn't in the database, you can't log it there.
We maintain our own (admittedly rather small) database of marks, and we have a category for those that are not in either the NGS or the Geocaching databases. These include PLSS marks, some county marks that we found interesting, etc.
Thed mark you found might be in the Washington Department of Transportation monument database, but they don't run an ongoing logging program. They do accept e-mails about errors or missing marks. The URL is
www.wsdot.wa.gov/monument.
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Our experience is somewhat limited--we've been doing this for about a year and don't find them in large numbers--but in that experience we have often found azimuth marks to be structures that can be sighted on from the primary mark. Here, though, it would seem that the azimuth mark would have to be occupied with a leveling rod or the like. If it were anything other than a disk, we suppose it would have a name other than "Home AZ Mark." We haven't yet encountered this situation.
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If a tower is replaced, it is very nearly impossible to make the replacement exactly the same height at exactly the same position as the older tower. We are talking centimeters here. So you are correct: the new tower would no longer qualify as the mark.
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Every so often we read here of a destroyed mark that hunters keep logging as found. It happens most often with towers and the like, because they get replaced, and so in the eyes of many observers are still there. A good example is FG1872, CLARKSVILLE ST POLICE RAD MAST, in Arkansas--a 300-foot tower that was replaced some years ago by a 100-foot tower. It’s been reported as destroyed a couple of times on this site, but folks continue to see the present tower and log a find. We ourselves feel a little like wet blankets when we post a destroyed report here, however useful such news may be to NGS.
This week we posted a destroyed report that will hardly be believed. Part of the problem is that the datasheet here contains no descriptive text, while that at NGS is pretty detailed. (To read it now, you have to check the “Include Destroyed Marks” box.)
The mark is SY2315, designated Tacoma Lincoln High School Flagpole. The mark was recovered in 1963 and in 1971, and clearly described as a flagpole on a high school at the corner of South G and South 37th Streets in Tacoma. It is still there, still in good condition. Not until the era of GPS receivers was it extremely easy to discover that this point is some 750 meters east-northeast of the ADJUSTED coordinates for the mark.
It turns out that the flagpole originally observed was at Whitman Elementary School, near the corner of South M and South 40th streets. The building was badly damaged by an earthquake in 1949, demolished in 1950, and replaced by the present Whitman Elementary School in 1952. The adjusted coordinates for the mark fall within the playground at Whitman, about 200 yards from the present building. When an NGS agent set out in 1963 to find it, he apparently settled for the high school without verifying the coordinates (that procedure was a late if not last resort in those days), and the present designation was assigned. Close readers of the 1963 recovery note may detect hints that a grade school was what had at first been sought.
So, though the point originally surveyed is lost, the flagpole atop Lincoln High School is still there, just as described in 1963. Though it is almost half a mile from its coordinates, a good many more people will probably see it and log it as found.
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The website www.surveyhistory.org has a list of the first serial number of each year for K&E transits; it indicates that yours was made some time in 1943.
Robert Parrish, of Weaverville, NC, runs a business and website devoted to the restoration, repair, and sale of these older instruments. The website is www.antiquesurveying.com. We have had dealings with him on a couple of occasions; in our opinion, he's an honest, engaging expert.
We're looking forward to going out in a few days with our 1935 K&E/Young & Sons instrument to see if we can turn an angle on a mark between an extant RM and one that hasn't been seen for a while. We'll let you know.
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Deb--
Thanks for letting us hear from you. We continue to send you every good wish, and thanks for the work you're doing. Blessings on you.
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Spoo--
In reference to point 2 in your first message, we also have found two datasheets whose coordinates appear to have been swapped, and they're adjusted coordinates. A couple of broadcasting masts. We haven't reported to NGS on these yet, because ownership of the masts has changed since the latest recovery reports, and we want to get to the courthouse to make sure we're talking about the right properties. We're pretty busy with other things right now, so it could be a while. But we wanted you to know that we don't think you're crazy.
One of us used to live in Brunswick, and enjoys hearing your reports from those parts.
Cheers,
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We attempted to thank Holograph and everybody else who runs up great totals. The reply went awry, thanked somebody called Hologram, and went somewhere. Thanks again, Holograph!
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Many thanks from us, too. We can't compete in terms of volume, but we have a high regard for those who can. And for Hologram's terrific lists.
Cheers!
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There is also a weird little biography of Ferdinand Rudolph Hassler, the "first US Geodesist". We're sorry not to have the exact particulars right now; we're still not moved in to the place we're renovating, and the books are all packed up. Something like The Tumultuous Life of Ferdinand Rudoph Hassler. It's rare, but has been reprinted. We might have found it on Amazon, or maybe abebooks.
Mighty informative, on rereading . . . .
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Many thanks, folks!
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We found a fairly unusual item the other day (see SY0758), and thought of looking it up on the marker-type list which we thought we'd seen posted in connection with one or another of the contests. Couldn't find it. Can someone send us there?
We're online rather infrequently these days, but will check back here when we can. Many thanks.
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For Cyclometh's benefit, we'd like to reiterate our apology for singling out one example, and our ending note that most of us have had to correct ourselves occasionally. We second the responses of those who urge Cyclometh to keep reporting.
Cheers,
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This is a pitch for special care in submitting handheld coordinates to NGS, with apologies for singling out one example. As we know, handheld coordinates can be useful when the datasheets give scaled coordinates. But if handheld coordinates are surprisingly far from the scaled ones, we might take the time to plot them on a map before submitting them.
The one example is SY0690, designated M 10, in Olympia, Washington. The scaled coordinates on the data sheet are 47 02 33 (N) 122 54 02 (W). These plot to within 60-80 meters of the described intersection of Legion Way and Washington Street. Not too bad for scaled coordinates; at this latitude the six-second margin of error measures roughly between 125 meters (east-west) and 190 meters (north-south).
The recovery note for 2005 gives handheld coordinates as 47 02 35.04 (W) 122 50 59.46 (N). The reversal of the latitude and longitude designations is a typo whose obviousness varies with the observer, but most of us will catch it. The 50 minutes in the (assumed) longitude reading is a less obvious error that puts the coordinates almost four kilometers west of the station, not far from Exit 107 off Interstate 5 in Olympia. A correction to 53 minutes brings the longitude well within the six-second margin of error for scaled coordinates, but who knows what the GPSr actually said?
Up toward the middle of the data sheet, we find that on the date of this recovery, the site was reported as not suitable for satellite observations. The 50 minute reading may not be a typo. In any case, it might have been better not to trust it.
We have ourselves learned this lesson from experience; it is not at all difficult to press the wrong key, or to put too much trust in a GPS receiver. As Paul says on the thread he started, several of us know how it feels to submit corrections to our own reports.
Cheers,
m&h
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I mean they are not accurate for NGS to list on the datasheet using that program. I thought that was one of the questions that was asked.
We see why you thought that! Our question about the accuracy of the procedure wasn't to imply that the coordinates thus computed might meet the NGS datasheet standards. As we understand it, you can’t pass the same order of accuracy from one single mark to another. Moreover, adjusted coordinates are adjusted from a number of coordinate pairs. You can’t do a least squares adjustment on one pair of coordinates.
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Scaled coordinates can be off by hundreds of feet, even if your GPSr is set to the same datum as that used by NGS. As we understand them (not without dimness), the differences between the two datum systems you mention are small, and are rarely likely to cause much trouble during a search. However, if you submit handheld coordinates as part of a log, they should be NAD83 coordinates, as that is the datum used at NGS.
Our experience has been that the To Reach descriptions at the end of the data sheet are more useful than the GPSr in maybe 90% of our searches, but we sometimes use the GPSr to refine scaled coordinates and submit handhelds as part of the log.
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Well, on December 23, we heard from Burt Smith at NGS that he will be adding a note to these marks saying that their elevations have changed and that they should be used with caution. We guess that's reasonable enough, since the marks are not of a high order of accuracy to start with. It seems reasonable also to place such a cautionary statement in any recovery note where such elevation can be documented.
Happy new year to all.
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We were playing around with the data on a recent find. It is CITY (EP0236) in Vaughn, New Mexico. It's a triangulation station, so it is equipped with two reference marks. All three disks are in excellent condition. As sometimes happens, each reference mark has its own PID (EP0238 for RM 1, and EP0237 for RM 2 -- odd reversed numbering, but there it is) and data sheet. A fat find for the score-minded, we'd guess. For us it was just one of those heart-leaps-up moments, on a low ridge above a seemingly dying town, in bright sun and strong cold wind. There they were, where they said they'd be. Anyway . . . .
The coordinates on the primary mark are adjusted. Those for the reference marks are scaled. But the "box score" on the primary mark gives azimuth and distance to each of them, so why not use the program FORWARD.EXE (from the NGS toolkit) to refine the coordinates? One reason in this instance, we suppose, is that the azimuths are given only to the nearest minute. But what about this? Is FORWARD.EXE sound enough for that sort of job?
Thanks for your thoughts.
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Well, we went back to Maryland, packed up for a move west, and hit the road again, all the while (or much of it anyway) turning over in our minds the matter of the tightly-packed clay in the casing of the rod at Okemah (FJ0761). Then one day in an antique mall in Adamstown, PA, for about a dozen bucks, there it was--a hand auger about an inch and a half in diameter and about two feet long with a sturdy wood T-handle. There's a picture of it in the log.
So today we arrived again at exit 221 on I 40, turned off, parked, and got to work. The end of the rod is about eight and a half inches below the level of the access cover--not that deep, as it turns out, but a mere trowel and the density of the clay had made it seem deeper. And we did locate the stamping on the lip, though it was worn and faint and tough to photograph.
A few hours later we were entering 74 south from Britton Road in Oklahoma City, and saw off to the right of the on-ramp a regular gaggle of witness posts--four of them, with an access cover in the center of the square they form. So we nabbed it, and pulled the datasheet later (FJ1359).
Some days you get the bear, some days the bear gets you, and some days you don't hunt.
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Back in June we wrote to an official of the FAA a couple of times to get information about whether and when certain radio towers had been dismantled or replaced. When she asked why we wanted the information, we explained what benchmarks and the database are, and added this:
The Survey makes grateful use of the findings of volunteer benchmark hunters, who go into the countryside trying to verify the information in the database, which is available to the public. In this way the Survey can be notified that a mark is still in good condition, or so worn that its stamping is illegible, or that it has been destroyed. Since many years can pass between “recoveries” of a mark, this work is essential, ongoing, and never-ending. Fortunately, there are numerous people like us, who enjoy looking for something that somebody else didn’t find, and being precise and cautious in the face of uncertain evidence.
BDT's wonderful paragraph says much more. We'd add that we like doing this together; our sometimes different approaches have a way of deepening the relationship as well as widening the scope of the search and the significance of the find.
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In a recent thread we characterized ourselves as fairly well informed and careful, among other things. We didn’t mean to sound boastful or smug, but the marker gods may have thought we did; they have brought us a lesson that seems worth sharing in some detail. If this gets too long-winded, we hope you’ll move on and forgive us.
For several weeks in August and October we were in the Coburg/Eugene area of Oregon, and found data sheets for survey markers in the curbing and road surfaces of several overpasses that cross Interstate 5. We got to three of them, found them, photographed them, and reported to NGS and to this site that we had found them in good condition. The fourth was not so straightforward.
The marks in question are PTS I5 15, (PID QE2191), in the Sprague Road overpass; PTS I5 17 (PID QE2154), in the Van Duyn Road overpass; PTS I5 18 (QE2155), in the Wilkins Road overpass; and, finally, PTS I5 19 (QE2156), in the Coleman Road overpass, which we reported not found as described, because the stamping on the disk we found was 1992, and the datasheet told us to look for a disk stamped 1969. Furthermore, while we found reference marks for the other disks, those for this last one appeared to have been covered by the installation of a metal guardrail and its anchor posts.
Lane County, Oregon has an unusually well-staffed and responsive surveyor’s office. We heard from Bob Thurman there that in 1992 this mark was included in a GPS Control project and assigned a NAD83/91 coordinate value, and restamped at that time. It was brought into the High Accuracy Reference Network in 1995. However, and it’s a big however, he adds:
"Sometime after that the Oregon Department of Transportation needed more clearance on their bridges and jacked up all the bridges along the I-5 corridor.
"This brings us up to today and the position on that monument is probably better than the original NAD27 position that was done in 1969 but is off from the last County adjustment in 1995."
Jacked up the bridges? Goodness gracious. So we asked the ODOT about all four of the overpasses mentioned above, and received this:
"The history of the overpasses over Interstate 5 is as follows:
Coleman Bridge # 081687 was raised 1' 8" in 1996
Wilkins Bridge # 08170 was raised 1' 7" in 1996
Van Duyn Bridge # 08172 was raised 1' 5" in 1996
Sprague Bridge # 08177 was raised 1' 7" in 1988 or 1989.
If we can be of further service please don't hesitate to call.
Jack Lee
District Manager
odot.state.or.us"
All four of these marks are survey disks of second-order horizontal accuracy; their vertical accuracy is not specified in the data sheets.
Although we reported the first three of these as good in August, we will be in touch with Burt Smith, who is taking Deb Brown’s mail while she’s away, to see what the NGS decides to do about these. It’s an interesting call, but elevating a disk a half-meter, more or less, has a somewhat destructive sound to us, no matter how easy it is to walk onto the overpasses, find the disks, and take photos of them. A steep spot on the learning curve.
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Marks Previously Not Found
in Benchmarking
Posted
The 1984 report in Paul's example reminds us that when "Not Found" reports are old enough, the searchers could not use GPS to counteract the loss of reference objects. In such cases, careful examination of the ground (did an Interstate come through here?
) and judicious used of the GPS can do what would have been much more difficult, even for NGS people equipped with theodolites and EDMIs, in 1984.