Jump to content


  • Posts

  • Joined

  • Last visited

Everything posted by Bill93

  1. In the national triangulation they used a carefully measured baseline about every so many tens? of miles to avoid a buildup of small errors in the triangulation. As mentioned above they were VERY careful in the measurement of the line. It was laid out with a theodolite and marked with temporary monuments at intervals. I think most baselines were on the order of 10 km in length, but haven't researched that. Besides all the other precautions, they did a level run so they could correct the surface length of each segment to a horizontal length. Temperature and tension corrected taping was only part of the care used. Each tape length was probably scribed on a piece of metal on top of a stake or more permanent monument, working under magnification. Here's a discussion of a base line in Nebraska. https://rplstoday.com/community/surveying-geomatics/geodetic-base-line-sign-dedication/ and one in California https://rplstoday.com/community/gnss-geodesy/yolo-base-line-1881/ There are some good links in those posts, as well.
  2. I don't know an exact answer, but in general pipe caps seem to have been popular in the later 1800's and first part of the 1900's, but much less common after 1930, at least around here. YMMV. There's a lot of information in this history, in which I didn't quickly find a succinct answer to your query. https://www.ngs.noaa.gov/web/about_ngs/history/Survey_Mark_Art.pdf
  3. I hadn't looked at the web form for a while, since I have been using DSWORLD. I noticed that the reporting email address has been changed. I suppose the Deb Brown address may have gone away. Now it is mailto:ngs.mark.updates@noaa.gov
  4. Many of us have used that designation for recovery reports for a long time. You can see it on many data sheets. When submitting to NGS keep it very businesslike-just the facts a surveyor would want to use to find it or to understand how carefully you looked before reporting NF. The old style was to be concise, but the current occupant of the "Deb Brown" chair will edit your report to complete sentences, spell out abbreviations, and insert metric conversions. So make sure your report can't be misinterpreted by someone who doesn't have field experience. If you use the form do your own metric conversions. DSWORLD is a better way to go than the web form because it has a Fornat button that does much of that editing, and you can check the results before submitting. I often re-edit its metric conversions to more appropriate significant figures, as I don't want my estimate of about 100 ft given to sub-meter precision. You can also put your handheld GPS coordinates into it directly (xx.x on seconds) instead of just in the text. When I started doing GPSonBM submissions GEOCAC wasn't an option (they don't expect geocachers to have precision GPS) so I started using Independent and Individual, which are the closest match on the two lists.
  5. Oops - sorry, yes it's Utah. I confused myself by having too many tabs open at once. You click the button for Designation and enter F 139 with the space. Right below that you can optionally specify the 2-letter state abbreviation.
  6. I used the advanced search https://www.geocaching.com/mark/nearest.aspx There are too many in the country for an easy search by designation to easily search without knowing the state. Seeing that most of your geocache finds were in Texas and California, I specified each of those and the designation F 139 (with space). The results were not disks set in 1962. However, trying some other Southwest states finds this likely candidate in Arizona that has many logs https://www.geocaching.com/mark/details.aspx?PID=HN0527
  7. The one marked BM 733 is likely a US Geological Survey disk, that may or may not still be there. I would guess it was never in the C&GS now NGS data base, because it is just a mile+ off of the D 17, E 17, F 17 line that goes north-south. USGS put in a lot of marks to help with the mapping work but most of them aren't in the NGS data base. It could also be some other semi-permanent feature instead of a disk, such as a chiseled mark on a culvert.
  8. MD0158 has a 2006 GC log saying the milepost is there but they couldn't find the disk. Could be the metal detector is needed, if the weeds and brush aren't too thick to swing it. It's a little unusual that his coordinates are east of the data sheet values. When using the data sheet SCALED coordinates remember that when they took them off the map they TRUNCATED so if the mark on the map was perfect the location is within about 100 ft north and west of those coordinates. But if the mark was made by measuring miles from a station, it could have been somewhat less than perfect itself, as noted for one of the other mileposts along here. MD0159 has HH2 coordinates taken from a GC log in 2006. GE doesn't show any obvious changes between the road and RR, so I'd say the finding chances are good. MD0160 was reported on GC in 2006 as probably destroyed, as they found what looked like part of the post and no disk. Note that they mentioned the milepost, so that is encouraging for the others.
  9. Further advice on railroad directions: When the crew wrote the descriptions they usually assumed some overall direction for the railroad and did NOT use a compass. So for MD0156, the railroad is described as running west. Thus their south is perpendicular to the tracks and not actual south, etc. It looks on Google Earth like the crossing may still be in use, so you have pretty good places to measure for that one even if the milepost has changed. You might want to confirm the crossing location on historicaerials.com MD0157 has HH1 coordinates, which means somebody found it much more recently but did not submit a recovery to NGS. I checked the OPUS Share list and find that the Ohio DOT submitted GPS measurements on it. The cm-level GPS data automatically gets put on the data sheet as HH1 quality, since it isn't quite up to full standards for full 5-digit coordinates. This one should be a slam dunk to find. https://www.ngs.noaa.gov/OPUS/getDatasheet.jsp?PID=MD0157
  10. My experience is similar to mloser's. If a post was placed at a road/railroad crossing it is nearly always far enough from the rail that you won't get hit by a train, and occasionally posts were added near the fence where there wasn't a road. Around here we have such a rectangular grid of roads and enough bridges and culverts that it usually wasn't necessary to set a post between roads. But the majority along a rail line are at the bridges and culverts only a few feet from the rail. If it's windy and no reason for them to whistle nearby, you might not hear the train until it is right there. And even if quiet and the inspection truck sneaks up on you, it could mean trouble. If I can see those marks in a quick look they can get reported, but I won't be digging dirt and ballast at a bridge on an active line or doing a GPS session that close. I thought 39 ft was the most common length for jointed rail. You can't be certain the joints are where they were in 1935, but if it gives "rails from the crossing" or from a signal the distance can help. Most of the major lines have since gone to welded rail which provides you no measurement. When we rode the train from Chicago to Arizona I'd gotten used to the feel of the train with some sway but not a lot of clickity-clack and then we hit the middle of Kansas where apparently jointed rail remains. Quite a difference in ride and noise. Distance from the nearest rail or center of the rails is a good indication, usually within a foot or two unless the line was re-done to add a set of tracks. If using height relative to the track, remember that many rail lines have been built up by added ballast, sometimes a foot or two since the bench marks were put in. The most common distance measure in old descriptions along railroads is "poles" which was a count of telegraph poles. If you can find some evidence of poles remaining anywhere in the area you can estimate the spacing along that line. Many were 40 to the mile (132 ft) but maybe longer and certainly shorter (e.g., 44/mile) in some areas. But extra poles could have been added especially around signals, stations, or rivers. There is a recreation trail near here that still has many poles standing at 132 ft spacing. Sometimes distances are relative to the mile posts. If you are lucky they haven't moved significantly, but when mergers happen the mile numbering sometimes is re-done. If you can get acquainted with a railfan (otherwise known to the crews as a FRN) in your area they might be able to show you old collectable track charts with the mile numbering on culverts and bridges closer to the date of the bench marks, which is a great guide but not necessarily to high precision. HistoricAerials.com is another great resource for figuring out where road crossing and former track lines used to be. There is one mark I reported as NF because it wasn't visible and I wasn't going to dig that close to the tracks. But looking at the old aerials I now think it likely the scaled coordinates at an existing crossing were a half mile off and the named whistle stop and mark were at a former crossing that is no longer there. That would depend on someone misreading a handwritten 4.7 miles as 4.2 miles, which seems conceivable. So gather your data, history sources, and evaluate the situation.
  11. Wow, Dave came up with info I wouldn't have known to look for. But he didn't address the general question of old vs newer elevations. The vertical datum in use has changed over the century and I don't have a feel for how much in a given area. First there were regional datums. I don't recall when the first national adjustment occurred. The NGVD29 national adjustment was used for the modern topo maps. Nowadays most work is done with NAVD88, but continuing work may stay on NGVD29. Corps of Engineers projects and city sewer systems for example may not have converted. Next there will be the 2022 datum that relies on GPS instead of old disks. I'd suggest you try to find a mark on the old topo that is also either on the newer topo, or else has an NGS data sheet with a superseded NGVD29 elevation in order to estimate the datum shift for the area between maps. The shift is likely to be small enough to ignore for map reading, but I can't promise that.
  12. Metal detector comments apply to abandoned railroads that have been turned into trails, also.
  13. There are poured-in-place bench mark posts, which around here usually had the top formed to about a foot square, and mostly done in 1934. By 1935 many were precast and maybe 6 inches square at the top. Triangulation stations typically were poured, round, and at least a foot diameter. You may find exceptions, but a given level run probably had all its posts made the same way, so compare others in the same run. A treasure-finder type of metal detector is a valuable tool to tell you where to probe. Ferrous/non-ferrous discrimination is almost necessary around railroads due to the proliferation of discarded hardware and sometimes iron-bearing slag used for ballast.
  14. https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=DQ8778 This works for me. The h-N computation means that the orthometric height (what people usually think of as ~elevation above sea level) was computed by GPS and a geoid model, and no level run was made to the mark. Since this is in remote northern Alaska, I can see why.
  15. Google, specifying site:geocaching.com and I suppose LT0708, but today that doesn't work so I can't reconstruct a search that works now.
  16. https://forums.geocaching.com/GC/index.php?/topic/300379-which-one/
  17. One of the professionals posted this. It hasn't been completed, but apparently USGS is trying to get scans done for all their data. This could give us more fun things to look for when we run out of CGS/NGS marks. I see nothing that says they will be looking for recovery reports, though, so maybe Waymarking will be the only way to record finds. https://rplstoday.com/community/surveying-geomatics/usgs-horizontal-and-vertical-control/
  18. Well, they say everything is bigger in Texas, but I hadn't heard that it applied to months. The Marshall Island location is what comes up when I look up the PID at NGS. It appears that Geocaching didn't load the marks in the Pacific, as that one doesn't appear. I note that NGS must not trust their Pacific geoid model to be as good as most of the US, since the ortho elevation is rounded more than the numbers that go into it. I think Ellipsoid Ht minus geoid equals orthometric height if it is GPS derived (or very close to it if the mark has a leveled height and it was a constraint on the fitting of the geoid). AA4433* NAD 83(PA11) ELLIP HT- 30.111 (meters) (06/27/12) ADJUSTED AA4433* LMSL ORTHO HEIGHT - 3.0 (meters) 10. (feet) GPS OBS AA4433 ______________________________________________________________________ AA4433 LMSL orthometric height was determined with geoid model OSU 91A AA4433 GEOID HEIGHT - 26.51 (meters) OSU 91A
  19. First order Marks are expected to be more accurate relative to their neighbors than second order, etc. The standards for methods, redundancy of measurements, and agreement of checks are tighter. I can't quote from memory but you can search for standards. Having more observation points for redundancy helps achieve accuracy, but degree is not specifically noted.
  20. Much of the generally useful advice can be found in the pinned threads at the top of the forum page and the FAQ at https://www.geocaching.com/mark/ The To-Reach description on each data sheet is very important for those marks having scaled coordinates. The challenge is to translate what might have been written in 1935 into today's world, and the research is sometimes interesting. The listing on this site is a snapshot of the National Geodetic Survey database as of 2000 or 2001, and does not get updated, so some newer marks and all more recent recovery reports to that agency are missing from this site. To see the latest, go to www.ngs.noaa.gov and pick Bench Marks. There are additional tools discussed in other threads on this forum that you can use to see them mapped. If you gain enough experience that you feel you can contribute useful information in a straightforward and businesslike manner, then you can submit recovery reports to NGS and they will appear on the data sheets. The NGS list has the most important ones for geodetic control, but as others have noted, there are many times that many marks out there set by hundreds of other agencies and companies.
  21. Assuming you are in Pennsylvania (you really should have told us that), this is your triangulation station. The others with the arrows are reference marks to aid in finding the main station if it is buried, as many were intentionally or otherwise. It has been measured with GPS as well as the old triangulation sighting data. Your Department of Transportation submitted the most recent recovery report on this disk. https://www.geocaching.com/mark/details.aspx?PID=KW3011 https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=KW3011
  22. The Alaska one is this: https://www.geocaching.com/mark/details.aspx?PID=TT2259 https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=tt2259 Somebody needs to submit a POOR condition recovery report on this one to NGS. Whatever bent the disk may have also altered its elevation, unless the 20-ft rod had hit bedrock.
  23. The first one is a land survey corner. Some of those have also been measured for precise lat/lon and/or elevation, but that is a secondary usage and it isn't surprising if those don't show up at NGS. The second one I would expect to be listed since it is a CGS disk, the predecessor name of NGS. You gave the same cords for both.
  24. I have a couple reports where my text as entered got modified to something confusing or silly. In one case I submitted "building burned decades ago" and it came out "building burned decades above the ground." I sent an email months ago and nothing has happened. DSWORLD has an option under UPLOAD for TEXT PROBLEM. But when I bring up this option it isn't clear what is going on and the help doesn't seem to cover it. I see all the text from the recovery reports on the data sheet, and can't edit it. Now what do I do?
  25. Today's setup for GPSionBM. I spent much of the day in a town library 5 miles away, well entertained and out of the heat. I called it a long enough session just in time to pack up and start driving as the first raindrops hit. Encountered a briefly serious rain partway home.
  • Create New...