jwahl
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Posts posted by jwahl
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GLO/BLM benchmarks are rare because the primary mission was boundary identification. I had a lot of them in Yuma area where the caps were used by Reclamation and others as BM's and stamped by them, but there were undoubtedly some sitiations where elevations were important to BLM. I did a lot of control surveys for photogrammetery throughout the west with levelling, but none of my monuments were published, but other situations could occur.
As to the idea of calling it destroyed, I am probably not up on the latest nuances in this forum for what 'destroyed' means, but finding a brass cap, does not mean that the monument itself is lost. As a benchmark (precisely leveled elevation mark) it could probably be assummed to be destroyed, but as a PLSS corner or GLO corner or a horizontal mark the pipe may still exist.
We found some brass caps that had fallen off corroded, graded, or eroded iron posts (which was the standard GLO monument after 1910 or so with lost caps. Corrosive soils could erode the pipe away to ground level. Actually the soils around Yuma would erode 1910 era GLO type monuments into flakes of rust, but they still had a magnetic signature with the metal locators until they were dug up.
Thus the position would not be lost just because the cap was found, but obviously the vertical integrity would have been almost totally compromised.
- jlw
A friend that works in the area brought me a GLO brass cap the other day (that he found in a gravel road) as he has heard me talking about BM hunting. At first i thought it was a weird cadastral marker. After closer examination, i realized that i have an actual GLO benchmark from 1911. Examination of the topo in the find area reveals many such markers. The one i have is marked for elevation 5601; the map BM at the found location indicates 5600 feet, i suppose an adjustment was made to GLO or BLM data here.
Coordinates as determined from google earth are N41° 50' 23.94" by W116° 14' 04.36".
I wonder if anyone knows of any info on these BMs.
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Well this post was a while ago, and our previous encounter was also. Nevertheless I am still ready to help, but I am not sure if you are still in the area. (MD/DC/VA). I could go other places but would need more information.
- jerry
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Since this is actually a GLO corner, you can probably find the GLO/BLM notes for it and get the actual true bearing (to about the nearest minute to the RM's.
- jerry
On the benchmark data sheets, seldom see anyone using magnetic bearings? ---
Off the road and back in the Yuma AZ area for a few days before starting my northward migration. Got a bunch of photos
to upload and NGS recoveries to submit; but do have an immediate question that kind of fits this old thread.
I run across several marks that used 'magnetic' in the description. I'm wondering if the headings were changed
when the Data Sheet format was instituted but leaving the word 'magnetic' in?
CZ2260'REFERENCE MARK NO. 1, A BRASS CAP SET IN CONCRETE BLOCK 7 BY
CZ2260'12 BY 30 INCHES SET 26 INCHES IN GROUND, IS 146.975 METERS
CZ2260'(482.20 FEET) EAST (MAGNETIC).
This RM 1 was found (POOR condition) at the given distance but due east of the GLO. The NOAA calculator gives a 14 degree variation for that
location in 1936. Since I found this one right on the true bearing I did not bother to calculate a correction for any others.
Am I trying to make too much out of this? kayakbird
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About the time that pgrig posted his original inquiry I did work with him via email and came up with a pretty good best fit conversion spread sheet. I used some simplistic math to do it.
A few months later he found documentation for the actual map projection used, but I suspect that due to errors in the survey I am probably getting about as good and possibly even better results than if I were to program the projection because I did a least squares fit to a reasonably large set of coordinate pairs and optimized my transformation over the area.
I have written to pgrig several times over the past year to ask how it is going, with no results.
I did find an article where he mentions it.
Wikipedia Article with mention.
as well as mention on his website:
and here
I would have to look back at our email dialog, but I think I had the conversion working at less than a foot at the 95% confidence level, but I don't really remember.
- jerry
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I'm still here. First thing to worry about on a used survey grade GPS is what is included and what is not.
1) How is it powered. Batteries, usually special types. You need to know if they are included, what they cost to replace, and how they are recharged and what the charger would cost. Don't forget to see if there is a power cable.
Someimes old units have batteries that have leaked and damaging the unit. Also there are sometimes internal backup batteries that start to fail after 8-12 years.
2) What about the antenna. Some units have built in antennas but the norm, especially for L1/L2 units is an external antenna. These can be very expensive if you had to buy one by itself. Also the proper cable to the antenna. The cable alone can be well over $100. Dual frequency survey grade antennas are typically $500-$800 used.
3) Software to communicate with the thing even if you don't have processing software. There are several versions of L1 only software available free on the internet, but L1/L2 usually costs quite a bit. Of course with dual frequency you can process it with OPUS or OPUS-RS for a single station. You have to have some kind of software to even generate rinex files usually.
4) There are two basic types of Survey Grade GPS receivers.
L1 or single frequency units. These are often much less expensive and are usually used for static observations requiring 20 minutes to a number of hours set up on a station. They can be found on ebay for from $400 on up. A new one would probably be about $2500 and up.
L1/L2 or dual frequency units. These can be found on ebay for typically $1500 and up and new would probably be 3 times that. Almost always require a special antenna.
Generally dual frequency units can be configured to do RTK or real time kinematic observations, but that may depend on the specific internals of the receiver. Also it requires another set of interfaces, for a radio link to a base and thus running two receivers. So that is one thing that runs the price up for a complete setup to in the $25K to $30K area. There are new ways of doing RTK these days that use networks of base stations accessible via the internet, but that is another story.
All survey grade GPS units are capable of obtaining positions to less than a cm, RTK not quite as good, but static sessions down to mm's relative to whatever network you tie into horizontal. Vertical is generally about half as accurate.
Static survey grade GPS must be post processed with some kind of software that sorts out all the data and computes a 'vector' from one station to another. This can be two of your own or one and a CORS station. RTK computes this in the receiver and also requires some kind of controller or data collector, another part of the expense.
There are resource grade receivers such as the Trimble Geo-XT type units that collect data that can be downloaded and post processed to the sub meter or cm level depending on the unit.
There are also receivers that are so old they won't work anymore due to Y2K type issues.
Leaves off here in Maryland, about time to think about Maryland Heights stations again?!
- jerry
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I haven't taken the time it deserves to examine your documents, but I notice that many of the observations were with a sextant. While they seem to be reported with a relatively high degree of precision, I am not sure if that is warranted. Perhpas there is more info in the documentation to explain this.
The other big thing that I notice (and others have mentioned) is what is the time reference? I do see observations for time which would mean astronomic time based on local solar noon meridian perhaps? Observations for many state boundary surveys in that era do have to be related to whereever they got the time. That involves transfer of the chronometer over distance and time with some drift. Then it might have been set by telegraphic time based on what.
One only has to look at other boundaries established with such means up until the 1910 era to realize there is considerable error there.
Now latitude should be darn close to true astronomic latitude, so that can be converted to a more modern geodetic value if you really know what ellipsoid was in use. I would expect latitude to be obtainable within a few seconds, however the sextant is of some concern.
- jlw
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Even bottle caps can be historic artifacts. I came across a large pile of them about 10 feet in diameter and 6 feet high in the California desert. It was in the vicinity of a major old WWII training camp, General Patton used for tank training. While there is very little else remaining at the site, it tells you something about there having once been a lot of significant activity in the area. The camp was probably most tents, but I have not studied it. My Dad was stationed there briefly in the runup to war. Tank training in the desert was in anticipation of action in North Africa. Then he got shipped out to Okinawa!
- jerry
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Sound to me like you found a newly set station named "AVEL" that was set this year 2010 with a witness post. It would not be QO2222, which is clearly described differently, set in a different year etc. even if it is in the same vicinity.
Anything set in 2010 will not be in the benchmarking database.
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Are there any agency designations on the witness post or cap?
- jerry
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Another thing to point out is that there is a hierarchy or chronology to how leveling was done and how it was/is used.
The primary lines of leveling were mostly done by C&GS now NGS to establish the higher orders of elevations across the country. In that exercise utility was not the primary concern, and so they follow easier and accessible routes to get from point A to point B generally following roads and railroads. Levelling cross country through the woods and over the hills and dales would be much more costly and prone to difficulty with increased error budget.
Later for mapping control USGS would run loops between those to wherever they needed elevations to control their mapping and generally to a lower quality since the use was less critical.
Other individuals or agencies such as transporation departments, water departments, reclamation departments, state, muncipalites, counties would do the same thing. Starting and ending their level lines or loops on NGS points and to various orders. Some of that may be high order and blue booked and monumented and some of it not.
Anyone needing elevations for a project, such as civil engineering for drainage of a subdivision, water project, etc. would essentially use whatever existing control was in the area and extend it to their project by work of their own. NGS's primary networks were not intended to provide elevations for specific projects, but to get elevations out into the general area for others to use or 'densify'.
Then there were various eras or campaigns of improvements or releveling by NGS to suit particular needs.
This is analagous to the horizontal network, where C&GS provided the first control, often only on mountain tops, USGS densified for mapping purposes. Other agencies bring control into thier areas of interest and projects and do the same everyday. Much of it not monumented but some of it is. This followed by some improvement and intermediate densification by NGS.
And the cycle continues again.
- jlw
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Using previous clues, I think they are called "post indicator" valves (PIV). The little window is to allow quick indication of whether the thing is open or closed.
There are still many models made
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I already admitted that the datasheet coordinate diff and HH1/HH2 designations are probably not due to any datum transformation.
But as a side topic. WAAS corrections while not a datum are with reference to base stations that were positioned to (WBS84 now ITRF00) coordinates, thus the value you get on your receiver will be corrected based on that and be OFF of NAD83 by a small amount. Once you are getting WAAS corrections and if you are set to NAD83 you are actually getting ITRF00 positions.
You can verify this by doing a very long average on a NAD83 point if you have a way of reading the coordinate out of your unit to sufficient precision.
Again now probably a side issue since the most plausible explanation is someone else reported the station with a HH2 capable device.
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Looks like a question for NGS.
Are you the source of the KMB description?
My mistake was interpreting the input coordinate as 45 16 30.3 instead of 30.5 in the HTDP transformation.
-jlw
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They may have transformed the WAAS values to NAD83. As I recall WAAS corrections yield ITRF00 values which differ by a meter or so from NAD83.
Not sure what epoch to use... My try below doesn't match for longitude very well, but suffice to say, the two values are shown with differing datums or epochs at least.
-jlw
HTDP (version 3.0) OUTPUT
TRANSFORMING POSITIONS FROM ITRF2000 (EPOCH = 05-01-2010)
TO NAD_83(CORS96) (EPOCH = 05-01-2010)
INPUT COORDINATES OUTPUT COORDINATES INPUT VELOCITY
test
LATITUDE 45 16 30.50000 N 45 16 30.48682 N 0.00 mm/yr north
LONGITUDE 123 00 44.30000 W 123 00 44.23858 W 0.00 mm/yr east
ELLIP. HT. 55.000 55.367 m 0.00 mm/yr up
X -2449483.046 -2449482.222 m 0.00 mm/yr
Y -3770100.191 -3770101.379 m 0.00 mm/yr
Z 4508956.985 4508956.959 m 0.00 mm/yr
-- or trying again using 1986 works a little better
HTDP (version 3.0) OUTPUT
TRANSFORMING POSITIONS FROM ITRF2000 (EPOCH = 05-01-1986)
TO NAD_83(CORS96) (EPOCH = 05-01-1986)
INPUT COORDINATES OUTPUT COORDINATES INPUT VELOCITY
test2
LATITUDE 45 16 30.50000 N 45 16 30.47544 N 0.00 mm/yr north
LONGITUDE 123 00 44.30000 W 123 00 44.25529 W 0.00 mm/yr east
ELLIP. HT. 0.000 0.382 m 0.00 mm/yr up
X -2449461.960 -2449461.583 m 0.00 mm/yr
Y -3770067.736 -3770068.944 m 0.00 mm/yr
Z 4508917.908 4508917.646 m 0.00 mm/yr
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Here are some of the things I am curious about:
RD1645 RTE WILSON R STA 1843+19.6 381.146 METERS 24836
...ON SLOPE BETWEEN WILSON RIVER HIGHWAY AND CONSOLIDATED
'TIMBER COMPANY LOGGING RAILROAD..
.. WALK E ALONG TRACK ABOUT 0.5 MILE TO NE END OF LONG TRESTLE, THEN GO NORTHWARD ABOUT 600 FEET TO STATION.
Also the topo shown by holograph isn't matching the road unless the road is half in the shadow. Shifting it to match the road looks to me like it puts it about on the HH2 coordinate plotted.
- jlw
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I commented briefly on this before. If the published coordinates are in some impossible location, then perhaps they ARE in error.
However that monument didn't look 'right' to me, as if it could have been disturbed. As I recall there are some other ties that it might be possible to check, otherwise the best check is a good position on it somehow.
And as mentioned, your handheld GPS can get off, particularly in marginal environment with any degree of trees and vegetation and perhaps a poor constellation at that moment in time.
Hard to tell.
- jlw
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I hesitate to ask, but given your coordinate problem, is there anything to indicate that there has been something like logging in the area that could have destrutively moved things around? Since the datasheet mentions a logging railroad, perhaps it is a possibility?
From the pictures it doesn't look like it but then things can overgrow a lot in 20 years or more, and it would be hard to tell from here anyway.
Given that the coordinates seem to fall in a worse or more unlikely spot, perhaps there is something else going on.
Also since it is third order maybe something really went wrong with the USFS data or survey.
A mystery remains.
- jerry
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Many of the states in that Area, MI, WI and MN have extensive programs to authenticate and remonument Public Land Survey corners. Usually a private surveyor is tasked with finding analyzing and putting GPS coordinates on existing evidence or prior monuments.
I think it is usually the county that pays for this. In some states the counties have peer review panels that then look at what the surveyor came up with. The idea is to stabilize boundaries of land which are based on the PLSS both with good evidence, reasonably good monumentation, described in a public record and then with a good GPS coordinate on it.
We might be able to devine what it was if we had a coordinate, or we can scope out the vicinity of your Post 54. As has been suggested it could be a point that just happens to be close to the line, or it could be a closing corner on the line, as two examples.
- jlw
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PS: My references to SugarLoaf relate to posts from a few years back where I thought there was some ambiguity about an old station versus a new station.
It was an example of where if you inversed coordinates in the NGS database you would get conflicting information about where they were from a few other clues.
I have not revisited that situation recently but remember it being an intrigue.
So I may be out of date on that situation.
But it was in a sense a classic investigative case.
Seems like I remember a debate that touched on similar issues up in the NY area where there were two stations allegedly 10 feet away from each other by datasheets. But where are they really?
- jlw
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I think there are these situations where maybe it goes beyond 'normal' benchmarking' etiquette, but where surveying may be applied. And the altruistic goal in the end is to find and document historic, if not otherwise important, points. Surveyors also have a natural historical bone or two in their make up and even historians and archeologists can claim some rights to the use of technology to 'find things'.
So here are some of the skills I can offer for some of these important missions 'insert mission impossible theme'...
I have transits, compass' and at least one theodolite and know how to use them. I can (if the skies are willing) obtain astronomic azimuth by solar or polaris observations that might help mapping some of these mystery areas. That is obtaining geodetically relatable direction that can be used to tie together objects in close proximaty. When woods are involved as they often are in the east, this usually means some traversing.
In addition I have tools to measure distance, but nothing that special, i.e. the EDM's I have date back 25 years and weigh a bit, but I also have a number of survey tapes. Taping requires some skill and more than one person usually.
And lastly I have some single frequency GPS equipment that can be used to get cm level positions with some patience and post processing but can be almost a one man operation if you can pack up the equipment which is mostly a tripod or two.
Also computational tools to work geodetically.
What I don't seem to have lately is much flexibility in time and to some degree much personal leeway to get away and do these things.
Helping others on a contributing basis is about the best scenario for my situation.
Finding an old mark is the stuff dreams are made of for surveyors. In my case, a retired one.
- jerry
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I have to think that there is a considerable possibility that the hole you show is it. Remember that it was probably drilled by hand and may have suffered a bit of erosion over the years.
In New England you see drill holes as monuments a lot, but they are more machine drilled.
That being said, I would love to be able to help by getting survey grade position on it at some point. There are problems with that though:
1) The station is listed as second order which to my intuition in this situation and with the apparent longevity of the observations, means probably within a few feet. I need to look at a modern datasheet to see if it is quantified by NGS.
2) Reliable results with finite occupation times are working against rapidly increasing canopy (leaf out) of hardwoods. So for a GPS session worked against a nearby station an hour might do it. If you had to work against CORS stations perhaps 4 or more hours.
3) My situation in regards to family health issues does not provide me with much of a chance to get away from home.
A good mystery is fun to solve. Almost easier would be a traverse from a good station to this area. However given the weight and quantity of equipment for 1 or 2 people to handle GPS seems like a good thing to try.
There is still a mystery at sugarloaf to explore.
Not to mention a few other very old stations in the EOA that are very close to me, but under threat of eminent destruction.
Maybe some of you with more energy and time can help me with that in return for some help at Maryland Heights?
- jlw
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Fine, but all of us who have been involved in surveying all our lives say that the term NORMALLY applies to a leveling point. As I tried to say... context may change that.
So in this case a "turning point" may mean an object that the describer understood to be of a "type" that would 'normally be' a turning point" i.e. some kind of round topped object.
Or perhaps the describer has enacted some novel term about a station where angles were turned. But that would be a rare application. Virtually every horizontal station before 1990 or pre GPS would have been determined by angles "turned".
It seems like a unique reference that can at best be described as ambiguous because the TERM means one specific thing!!
Yes it is obvious that is probably what this station IS. But what was in the head of the man in the party that described it? And what was that person's experience?
I still say that the description MAY possibly be of the the 'point' monument 'type' as being similar to what would NORMALLY be a good turning point i.e. a bolt or object with a rounded top surface.
I just don't think the term was normally used to refer to any station where "angles" were turned. That would be on almost every horizontal point between 1760 and 1986" wouldn't it? And do you see that anywhere?
- jlw
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I also know the word to refer to a point or object used to set a rod on during a leveling run. Often something with a rounded top. In this case they may have used a physical object 'used' for turning points as a the referred to station object.
If the point is a horizontal mark on top of a grain elevator or such then in context I guess you could say it meant something else, but this description is a bit confusing. Center bolt of what? Occupiable? Anyway it may be moot if you can find this bolt.
Note the actual data sheet describes in more detail "
MARKER: B = BOLT
SETTING: 35 = SET IN A MAT FOUNDATION OR CONCRETE SLAB OTHER THAN
WITH SETTING: PAVEMENT
So I would guess a bolt set in the center of a concrete slab. What they meant by turning point may remain an ambiguous mystery.
- jlw
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I would concur, it may be a BM or control point, but most likely a property corner for a National Park, or monument or something of the sort.
- jlw
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I am in the general area and have the capability to get a 1 cm precision GPS position that could possibly be used to verify or qualify what you found.
It seems unusual to me that a rod or rebar type monument would be accepted by NGS, but you never know.
Email me if you are interested in positional verification. This would be on a hobby basis since I am not a licensed surveyor in MD.
51 feet would not necessarily be out of limits for error on a conventional recreation grade GPS unit, although with WAAS and the right datum and open sky one would expect it to be within 20 feet.
jwahl@qubicle.com
- jlw
Any idea what these mystery nails are?
in Benchmarking
Posted
I surveyed many years for BLM and one of my unusual jobs was doing control for photogrammetric surveys. We would often panel corners within the flight lines so that the maps could be registered to the PLSS easily. The photo panels I would set were 18" wide material in the shape of a cross or Y centered on the point each leg being 15 feet long. I often fastened these to the ground by driving in 60p nails sometimes with various things like milk bottle caps to keep them from tearing through the material. Mine were white plastic but some may have used fabric. After a while weeks they would be torn up by cattle and the wind and the only think left is the nails, probably lasting only a few weeks at best, but serving their purpose once the photo flight lines are done.
A 60p mail is about 6 ins. long. First thing I thought of with your post is something relating to photo panels. Photogrammetry has been used on all kinds of projects from locating roads and other improvements. Some of my jobs were in very isolated places. Private surveyors have been doing the same thing for years. I could probably find you a photo of one of my points by way of illustration.
- jlwahl