NGS Surveyor

An NGS field crew just sent in a photo of a standing Bilby Tower. This may be the last standing Bilby! The photo was taken in April 2009, see: http://www.flickr.com/photos/12262796@N06/3533218157/ . This 64 foot tower is in pretty good condition considering its age. Note at the very top on the left, a round pole has been added. This may have held some sort of antenna . The very top of the tower is the “triangle head” which connects the three legs and holds the “lightplate” (nicknamed the meet-plate). One of the three floor boards (plywood) is missing. The steel parts, even though galvanized, have quite a bit of rust. The tower also has several guy wires. These were normally not used because they caused the tower to vibrate if there was any wind. For a diagram of the parts of a Bilby Tower see: http://docs.lib.noaa.gov/rescue/cgs_specpu...5U352no62-3.PDF , page 70. For a photo of the triangle head and lightplate, see page 75. The center hole in the lightplate was plumbed over the center of the mark and then one or more lights were bolted on and aimed at adjacent stations. The theodolite (instrument to measure angles) was affixed to the plate mounted on top of the inner tower. The inner tower plate is also still in place, although it is hard to see in the photo. For a paper I wrote on Bilby Towers, with lots of photos, see: http://celebrating200years.noaa.gov/magazi...come.html#intro . This Bilby Tower is built over Triangulation Station COUBA in Louisiana. The mark was set in 1972 by the National Geodetic Survey. The mark can only be reached by boat. The PID is AU2876. If anyone knows of any other standing Bilby Towers please sent photos and locations. I have heard that there is one at Cape Canaveral and many years ago there was one at station MINN PT SOUTH BASE (PID = RN1508) on Minnesota Point, an island which forms the harbor for Duluth, MN and Superior, WI. The top of the tower had been removed due to the nearby airport. Thanks, GeorgeL NGS

Yesterday, one of the "rest of the forum readers" requested a copy of the "Marks" paper and I emailed it to him. He agreed to review it and send comments. Yes, I could have emailed the request, rather than posting, but I don't have a list of those that have the paper. And, I don''t have the time to look through many months of emails trying to figure out who I sent it to. GeorgeL NGS

I have sent several GC members a copy of my draft paper on USC&GS, National Ocean Service, and National Geodetic Survey marks. I'm about to update the paper and hopefully get it posted on the NGS www site. So, I request any and all comments from those who have copies. Please submit by the end of May. I'm looking for typos, unclear information, and, of course, errors and omissions. Thanks, GeorgeL NGS

m&h, Wow, you found a mark reported as destroyed in 1922! Your photos came through fine, thanks. This is one of the 4 variations of the old “cup” style disks. (#1 – Two slashes completely across inner circle (yours), #2 – Two shorter slashes that do not go completely across the inner circle, #3 – A triangle in the center with no slashes, and #4 Nothing in the center (perhaps a punch hole)). From your description of the present situation and the statement in the old descriptions, it sounds like the boulder was moved, probably during road improvements (and this could have happened between 1913 and 1922). Klemmer & TeddyBearMama (and TheBeanTeam), Thanks for the photo of the old MAGNETIC STATION flat disk. I’m always interested in any of the rare, old, flat USC&GS disks (I’ve never even seen one in person.). These flat magnetic station disks were used from c1912 to c1921 and curved top MAGNETIC STATION disks were used c1921 to c1970. GeorgeL NGS

This is an NGS disk but it was used as a “tidal” bench mark, probably by a survey crew from NOAA’s CO-OPS office (maybe they were out of “NATIONAL OCEAN SERVICE” disks). Some tidal bench marks are in the NGS database but most are in the CO-OPS database. Here is the link to the CO-OPS database for bench marks in California: http://tidesandcurrents.noaa.gov/station_r...;id9=&id10= . CO-OPS is the NOAA office that handles tide and water level measurements and computations. Note, in the above paragraph when I used the term “bench mark” I mean vertical control points only. NGS stopped stamping elevations on disks many years ago (because the elevations change after newer survey work and/or newer adjustments), and NGS also has the policy of not stamping on disks of other agencies. There are some USC&GS and NGS disks that have never made it into the NGS database. Some of these were surveyed with third-order procedures and since NGS stopped accepting third-order work many years ago, these were not added to the database. Some marks were set near the end of a field crew’s season with the intention of surveying them later that season. Then, perhaps, bad weather or some other reason kept them from being surveyed. Also some set near the end of a season were not surveyed the following year because the field crew was sent to another location. GeorgeL NGS

Whether it be paper or digital, the point here is to take a copy of the datasheet with you when searching for survey marks. Almost every day I see here people lamenting that the mark is not where there GPSr takes them - but the description on the datasheet would have taken them to the mark. GeorgeL NGS

PapaBear, Yes, there was a change in the output. Those results were formerly displayed to only the nearest second but are now displayed to 5 places. This was done to improve the plotting of points on an interactive map. GeorgeL NGS

I used power drills to set disks in the late 1970’s (Wacker and Cobra models). I also checked USC&GS Special Publication No. 247 which was originally written in 1950 and updated in 1959. I did a digital search and the 1959 version does not mention power drills at all. My next step was to email a retired USC&GS employee who hired-on in the 1950’s. I asked him when the first power drills were used by the USC&GS and his answer is “1959-60, the Cobra Copco, in Plainfield, NJ, Party 607 (later G-19), Chief of party LT V.B. Miller. They also came with a space bit which made them useful in hard digging for anchor holes” (for Bilby Towers). As a side note, I was chief of Party G-19 from 1978 to 1980. GeorgeL NGS

Here's a photo of a 500# stone being lowered into place: http://usasearch.gov/search?v%3aproject=fi...amp;rpaid=& . Note the name of the guy on the right, J. Bilby, the inventor of the Bilby Tower. I have never seen a circle cut in stone like that. As far as I know, star drills were used. But this was a USGS disk, not a USC&GS disk. GeorgeL NGS

Sam, Please define what types of survey marks you are including in the term "bench marks". Different people use different definitions. Thanks, GeorgeL NGS

I look through the Gallery regularly, especially looking at the close-ups. I have found quite a few unusual marks this way, just last week I found a City of Los Angeles disk with the factory stamping "Bench Mark U.S.C & G.S. Datum". Most of the photos in the Gallery are excellent but there are still some with debris on the mark, shadows across the mark, and/or fuzzy focus. GeorgeL NGS

JBAnderson, Thanks for submitting the photos. I have heard that this type of mark was used as an intermediate vertical control point, but in this case it is a second-order horizontal point. The last line of the description states "The center of the mark was intersected.". This makes it sound like the mark was positioned by the intersection method (sighted upon from three known points), but in that case it would most likely be third-order rather than the second-order stated. If you would like to see what one of these looks like in new, unused condition, see: http://www.flickr.com/photos/12262796@N06/3459011317/ GeorgeL NGS

Regarding the flatness or curvature of USC&GS and NGS disks, the very old USC&GS flat disks were dead flat from edge to edge. The curved disks have a uniform curve from edge to edge. For photos of the old flat disks, see my photo gallery on FLICKR, and I just uploaded a JPEG drawing of a 1985 disk order showing that the spherical radius was 5 inches. See: http://www.flickr.com/photos/12262796@N06/3449543899/ for the disk drawing and browse through the images for the flat disks. GeorgeL NGS

DaveD and I just talked about station RANDELL. The “2” mark was probably established by the NGS Mark Maintenance person for Arizona (in 1980), L.W. LW’s boss was CLN, the initials on the Datasheet. Both DaveD and I know these two individuals, both of whom are now retired. The other clue is that RANDELL 2 has a third-order position. If an NGS field crew had set RANDELL 2 it would most likely have been second- or first-order. So, what happened to the directions and distances to the RMs? Well there are several possibilities: (1) someone forgot to include them when the information was keyed in, (2) since it was third-order, the data might have been purposely left out, or (3), there was no known initial azimuth so that the azimuths to RM 3 and RM 4 could not be computed. Our database person looked and the data is not in the NGS database, he said he will look in the old paper records. Just before I was ready to post this, our database person showed up at my desk WITH THE MISSING INFORMATION! The data was not in the database because of a problem with the initial direction (#3 above). But I think there is enough information to get what you need. So here is the info: Angle observed at RANDELL 2 Direction to RANDELL 65 deg 10min 24.5 sec Direction to RM 4 131 deg 30min 09.5sec Direction to RM 3 257deg 18min 50.1sec Distance from RANDELL 2 To RM 4 7.340M To RM 3 7.786M So, you have the positions of RANDELL and RANDELL 2 (from the Datasheet) and can do an INVERSE computation between them. That will give you the azimuth from RANDELL 2 to RANDELL. Then subtract the directions above to obtain the angles from RANDELL to each RM. Then add each of these angles to the azimuth found above and you’ll have the azimuth to each of the RMs. Clear? Good Luck! I will send the same guy the information for the other station and we’ll see if he can find anything. Regarding stamping on RMs, in 1968 a booklet of rules for stamping disks was written. The rule for this case required that the RMs be stamped with the date they were set. RM 3 and RM 4 were stamped in 1980 according to this rule. Of course, years earlier the rules may have been different or there may not have been any rules. This booklet is not presently on-line, but I hope to get it on the NGS www site this summer. GeorgeL NGS

Shorbird, Thanks for the info. I looked it up on GoogleEarth and its not too far from my cousin's place. The datasheet states it was set in 1963 so that agrees with the date you found on the cover. I recall that NGS did some work near Akron in the early 1970's, so it may have been a continuing cooperative project. NGS worked in GA for many years and also in CT for many years, both in cooperation with state survey agencies. Harry Dolphin, Interesting disk, but Difficult Run is correct, I'm looking for USC&GS and NGS disks, thanks. GeorgeL NGS

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

WOW Shorbird - that is the first CITY and USC&GS disk that I have ever seen!!! Definitely a nice find. Especially interesting because I still have some family living in Akron - I'm originally from Cleveland. Where in Akron is it? BillWallace - Hard to tell, but I think your photos show curved-top disks - I can see some light under the ends of your straight-edge. See: http://www.flickr.com/photos/12262796@N06/...in/photostream/ . The two disks in the photo are dead-flat. They do show that some flat disks had 3 rows of printing. Regarding "J 1", I'm not sure what happened but it does state that the building was moved. I have found a 1916 USC&GS specification stating that the name and date should be stamped on disks, and have seen early disks with no date stamped. So, my GUESS is that the disk was set in 1906 with no date stamped and that in 1924, after the move, the year "1924" was added. GeorgeL NGS

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

Thanks for the several recent photos. AstroD-Team – Your TRIANGULATION STATION disk, BANK 1921 is indeed unusual with that large triangle stamped in the center. The TRAVERSE STATION disks have a larger triangle than the standard TRIANGULATION STATION disk, but this looks like it could be even larger! Shorebird – In my comments several days ago I mentioned that the hole in the disk was an air hole, but I forgot to explain what the air hole was for. The theory was that the hole would allow air to escape from behind the disk as the disk was pushed into the wet cement, resulting in cement completely filling in the concave area behind the disk and making a stronger bond and hopefully a disk harder for a vandal (or nature) to dislodge. Harry Dolphin – The 1909 disk indeed looks flat. I’m waiting for someone to take a photograph of a flat disk with a ruler laid across it to prove that it is completely flat. Your photo of the USC&GS AND STATE SURVEY disk really caught my attention. The 1956 date seems completely out of place since I had only heard of this type of disk being set during the 1930’s. I looked at the description and it has 1956 all right, BUT, it has two entries with the 1956 date, one entry that the disk was set in 1956 and another that it was recovered in 1956. This is possible, but somewhat unlikely. I have often seen the datasheet for these …AND STATE SURVEY disks having UNK (unknown) as the setting date. So, this could have been an error made when the original record was typed into a computer record. A former NGS State Advisor to NJ presently works in NGS so I asked him if he knew when these …AND STATE SURVEY disks were set in NJ. He didn’t know, but he did have copies of some old station descriptions and he found the one for “801”, see: http://www.flickr.com/photos/12262796@N06/3405471774/. See the dates 1939 and 1941 in the upper right corner. My guess is that the disk may have been set in 1939 and surveyed in 1941. So, even if its 1939 you are still outside the original range of dates I gave for this type of disk of c1933 to c1935 – GOOD WORK! GeorgeL NGS

Shorbird, Which part of the stamping did you mean was unusual, the name SLEEP? This disk is a little unusual in that it has the air hole just above the "1" in 1958. This air hole was used in disks for several years in the 1950's until it was realized that some people were setting up their survey instrument over the hole instead of over the center of the triangle! GeorgeL NGS

Yes, your photo is of one of the cast iron disks from WWII. I read somewhere that the letters were larger because they couldn't cast small letters in the iron disks. GeorgeL NGS

Mega Scooter, Very nice find! Your disk appears to be flat-topped and is 4 years earlier than the start date I had given. I looked back at my spreadsheet of disk type history and the dates I gave earlier for the MAGNETIC STATION (MS) disks were for the curved top MS disks. The flat-topped disks were listed in my spreadsheet but I missed them in my quick review. The flat-topped MS disk first shows up in a USC&GS Special Publication in 1912 (S.P # 15, page 23), see: http://www.flickr.com/photos/12262796@N06/3351680168/. It appears in a photo again in S.P. #20 in 1914. A disk is mentioned with no photo in S.P. #51 in 1918. Then in 1921, a set of five curved top disks is first shown and includes a MS disk (S.P. #74). So, your disk is the earliest MS disk that I have seen a photo of, thanks! GeorgeL NGS

VagabondsWV, I did an “inverse” computation between your GPSr position and the published position for CHARLESTON MAGNETIC and got 5.6 meters. (Using the “inverse” computation on the NGS WWW page.). So, the mark you found is most likely the correct mark – I thought there could have been another nearby mark. I plan to stop by one of these on my next trip to Ohio. Regarding the MAGNETIC STATION disk, they came with the 6-pointed star in the center. They were used from c1921 to c1970. GeorgeL NGS

Very interesting that there are two of these old "cup" type disks. DaveD and I just talked about this and he looked up in several old reports trying to find mention of these points. We didn't find anything. So, there appears to be two possibilities: 1. These disks were set much earlier than 1944 as magnetic, vertical control, or some other type of usage and then reused in 1944 as magnetic stations and had reference marks and azimuth marks added in 1944, or 2. As I suggested earlier, perhaps the 1944 surveyor found a stock of these very old "cup" type disks and decided to use them. GeorgeL NGS

VagabondsWV – Your disk qualifies under “A” and is VERY rare. The only one I’ve ever seen is mounted on the wall in the NGS office in a display. However, I don’t understand the setting date of 1944 that the description states. To my knowledge, these old “cup” shaped disks were only used from c1900 to c1912. Do you have another photo without the shadow over the disk? Could you send me the latitude and longitude that your GPSr read? Did your GPSr position agree with the description’s position? Did you find the reference marks and azimuth mark? Did they agree with the description? What factory and user stamping is on those disks? Did you check the distances and directions from the main disk to the reference marks? Did they agree? If everything does agree with the description, then possibly some USC&GS surveyor found the old disk at the bottom of his box of disks and decided to “use it up”. Very interesting! GeorgeL NGS