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Bill93

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Everything posted by Bill93

  1. Stupid question time. I realized that I haven't been paying enough attention as I find elevation benchmark disks (as opposed to reference marks, etc). In the future, I'll try to remember to check their rotational (azimuth) orientation. Meanwhile, any knowledge from the group would be welcomed. They have a long horizontal line (as the lettering reads) and a short cross vertical. I would expect that when placed vertically the long line would be level, but haven't actually seen any of those yet. When placed horizontally, are they oriented in azimuth by any rule and if so how consistent are they? I don't think they all are aligned with the lettering to read while you face north. What have you seen?
  2. I'm not surprised this is not in the NGS or Groundspeak data base. I have found 3 similar ones down here a couple counties away that were not listed. Like yours, they are "US Coast & Geodetic Survey and State Survey" with the county number stamped near the outer edge of the clear space and a serial number in the middle. The digit 7 off to the left would be Black Hawk county, which it is within. The serial number is either 76 or 761 with a very slanted 1 This series must have never been worked up with the computations to put them in the data base. The station BLACK you were originally seeking is set up like a triangulation station, although it is just listed as "survey disk". Tri stations typically have 2 reference marks nearby, and an azimuth/reference mark perhaps a quarter mile away (this one uses a landmark instead of an azimuth disk). The reference marks are most often along a road right of way and can often be found without too much trouble. BLACK is a newer style mark, on a deep rod, and is buried. The "surface mark" for the older (1930's) tri stations around here is usually buried 12 to 20 inches in a cultivated field. The REAL mark, which even the NGS doesn't look at except for the most serious work, is about 4 feet deeper, with the surface mark carefully aligned over it. To claim a find on a station, you need to find the surface mark, not just the reference marks, and I haven't been digging them up due to the bother of finding the right person to ask permission from. It is quite useful, however, to report on the condition and coordinates of the reference marks, and the sky visibility of the probable station location. I read some of your other logs and see that Black Hawk county has quite a few more recently placed stations that aren't buried, although they do have reference marks. All the tri stations I've looked for are the older buried style. I expect the first one I'll actually see is MG0879 AVIATION RESET down by Iowa City as it isn't covered up by anything but a pool of muddy water.
  3. Early in this thread, there was mention of the large discrepancies seen in scaled coordinates. Scaled means somebody plotted it by description on a map and then used a scale to read the Lat Long values. I plot the difference between the listed and my measured coordinates for the marks of a given era I find in a given county, and find the average offset. Then when looking for another mark of that type, I apply that offset to the listed coordinates so I start closer to the right place. It can mean the difference in picking the right culvert or unnamed cross street. Locally the 1930's marks tend to be found 150 feet NW of the published values. Despite the 6 second tolerance quoted, I have found the majority of the marks to be within a little more than plus or minus one second, after adjusting with this offset. The offset changes significantly around the state, and then occasionally you get the zinger that is off the full 6 seconds. Pay close attention to the date of the mark and whether it is scaled or adjusted. Triangulation and intersection stations are adjusted, and will almost always be within handheld GPS accuracy. Newer marks will often be scaled from a more accurate map than the old ones.
  4. I found MG0512, designation '8', as described in good condition, but its record at NGS is marked destroyed. I am waiting to finish a roll of pictures, and will then try to explain this to Deb. Will NGS restore it to the active list? I was lucky enough to guess its PID "in the cracks" between other PIDs in the area to find its record. If anybody knows a better way to find the record of a destroyed mark, please post it because I have more to look up that I haven't been able to guess. This BM is interesting to me because another mark designated '8 RESET' about 50 miles away is mistakenly listed with the same Lat Long and I'd like to get that straightened out. Actually there are 3 pairs with the Lat Long problem. But one thing at a time. A 1975 log by NGS shows MG0512 marked destroyed, but the wording seems wrong. I think it was posted to the wrong PID because it says 'Surface mark reported destroyed' which sounds like a triangulation station. This is is a bolt embedded in the concrete of a bridge railing so the words make no sense here. There is a recovery log in poor condition by USPSQD in 1995. I suspect that the reason they called it 'poor' is that a bolt looks a little (not a lot) like the stem a BM disk would be attached to. It looks to me like it is in as good condition as the day the concrete set. But why did NGS post their 'Recovered' on the record of a 'Destroyed' mark? Any advice on this mess from you more experienced folk? BH
  5. I would also suggest reporting the sky visibility for satellite measurements, relative to the NGS standard which I think is "clear from 15 degrees above the horizon in all directions, except for a few isolated small obstructions". To report to the NGS using the on-line form, you have to check "Yes" or "No" about this so it is a good idea to have the info in the Groundspeak entry also. I tend to err on the "favorable" side when selecting Yes/No but may mention "marginal visibility to the south" in the comments if I'm unsure. Better to have the pros drive by and say "I don't like that site" than to make a possible candidate fall off their list.
  6. I presume that these records were kept in file cabinets or boxes of file cards for decades, and new information was added occasionally on the same piece of paper. Then somebody got funding to keypunch data from those papers into computer format. So the record for the 1935 disk had a note added to it about the 1942 disk and when the data was keypunched they put it all under the original date instead of making a separate record. The 1942 note says the land was acquired by the US. What was this area used for during the war? There might be a clue there as to why a new disk. Probably they were placing a series of disks for some wartime purpose and wanted all the disks in the project to have identifiers in the same series. They also probably reasoned that they could re-use data from the old disk interchangeably with the new to sufficient accuracy and less work. That's my speculation on it. BH
  7. I've got one (LE0255) that has been painted with aluminum paint and you can't read any stamping. I plan to take some organic solvent type paint remover (laquer thinner, and maybe carburator cleaner) next time I go there and try to soften it up enough to wipe off with a towel. Any advice? BH
  8. I would agree that the mark is not under the paving that is referred to. But it very well could be underground or under newer paving. It might even have been intentionally buried. This is a horizontal control station. In my area nearly all of the horizontal stations (triangulation stations) set in the 1930's to 1950's are buried. They have a "surface mark" typically 18 inches down in soil (not too many rocks available here) and the true mark about 4 feet lower. They are a disk in a concrete post sitting on top of another disk in a post with careful alignment to keep one precisely over the other. When you look for them, you only find the reference marks. If you can't see the (buried) surface mark you can't log a find on GC.com. Bill93
  9. Are there other on-line data bases besides the NGS one that we can check for descriptions of these marks? I have found (in a month) in Iowa 2 "US Coast & Geodetic Survey and State Survey" markers and one "US Dept of Interior Geological Survey" disk that aren't in the NGS data base. The latter one is beside a surveyor's orange stake with an elevation to 0.001 foot written on it. The elevation is not stamped on the disk and nothing else around seems to have elevation numbers. Where did he get the data? It would seem to this newcomer that Groundspeak would be doing the world a favor if they provided a place for people to report these. They could use the same mechanism as for new geocaches, with a moderator approving the initial submittal as being a "reasonable" entry. If one of these marks were reported in good condition and with good satellite visibility, then maybe it would be more likely to get adopted into the NGS data base. I can see that they can't put the effort into checking thousands of other agency benchmarks to find a few good ones but with pre-screening like that maybe some could get used. BH
  10. Repro benchmarks/reference marks?? That is like making repro coins. They should be required to plainly mark the image as a copy so nobody could mistake them for the real thing under any circumstances. I can imagine somebody out searching while wearing a belt buckle made from one and getting arrested. BH
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