Measurement issues in providing reference measurements to locate existing monuments

Two stone examples:

I went through most of a township. 

The first example is a found marked firmly set stone, 140 years in place so I left it without setting a monument.

I located what I felt was the centerline of the top, it is more plumb than you might gleen from the picture. Three years later after a bunch of activity and utility layout and surveys from others I return to locate it again and there is a shiny new cap next to it about .8' north, I locate the center of the stone again and I'm less than a tenth. What to do about the cap, nothing for me. Most stones in the area are in poor condition and I set a monument and bury the stone alongside, trying to centerpunch the hole made by the stone's removal, it's a total eyeball thing. 

The next stone:

The notes said something like 6x5x1 and you had to read it carefully to notice it was 6x5x1 feet, not inches like 83 of the other 85 township corners. 

I estimated as best I could where the center of the stone would be if plumbed, it is leaning to the east, and set a cap there, that hard to see shiny silver cap is a 3" cap, gives a bit of an idea how big the monument is. So for one I decided to not set anything for the other I did set one and I left both stones in place. Almost every other found stone got a new cap and a buried original stone. 

I did find in the next township a BLM brass cap with a nice set stone about 20 feet dist from it.

Posted by: @holy-cow

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One example is locating the corner of a building.

I like one method that I've seen on these forums involving shooting reflectorless twice on each building face and calculating the intersection point, which would be the building corner. One could argue that aberrations of the building wall surface might influence the accuracy of such measurements.

Posted by: @holy-cow

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When using a prism and prism pole to get that measurement, do you report whatever the gun tells you or do you add a half inch or whatever is the difference between the "point" created by the prism and the similar point on the rear of the prism assembly?

If memory serves, the offset distant is set in the gun. You record the distance the gun tells you.

Posted by: @holy-cow

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If the future surveyor measuring that reference distance uses an identical prism he will get a number that is different from the measurement found by using a steel tape for that short-direct reading.

I was taught that EDM distances less than 100' are not as accurate as a steel tape. If you agree with that, then the measurements should be different.

When I started as a chainman on a Nebraska Dept. of Roads survey crew, our field equipment consisted of a K&E 30" Paragon transit, a 100-foot cut chain, plumb bobs and a hand level; no prisms or EDMs. I am solo now with a Leica GS18i GNSS receiver and a Leica MS60. My GS18i has tilt compensation. When I shoot buildings, I collect two sets of observations. I orient the rover's tilt to be in line with one wall then the other wall. The error is usually +/- 1 cm for position and 1 cm for the tilt. The GS18i also has a terrestrial camera that takes a photo every 1/2 second. I use it for instances where the obstruction of the building creates inferior positions when the rover is next to the building.

If I determine I need better accuracy than what my GNSS receiver can provide, I get out the MS60 and AP20 pole (it also has tilt compensation). I follow the same procedures as for the GNSS rover regarding orienting the tilt to be in line with building walls. The Leica AP20 pole can have the prism at the top of the pole or mounted at the bottom of the pole (the prism is 1 foot above the pole's pointy end). The MS60 has an EDM error of 1 mm +/- 1.5 ppm. With this configuration, the combined error of the tilt and distance is normally +/- 0.02 feet (2 mm for the distance and 3 mm for the tilt error).

Regarding HC's second question of original stones decorated by an adjacent modern monument, I usually sigh when I see this. One example is a 1930 GLO dependent resurvey of a corner on the Ninth Guide Meridian West of the 6th P.M. The GLO surveyors set an iron post with brass cap snuggled up to the west face of the original stone. I have heard that some of my peers will set a modern monument next to the original stone to let everyone know they found the stone. One reason that I can abide with is that they set the rebar and cap so that they can find it with a metal locator during the snowy part of the year.

Being a geologist, I always carry my Brunton International compass that I purchased 44 years ago when I was in geology school. If the original stone is leaning, I take the equivalent of a strike and dip of the stone. In other words, I measure the direction that the stone is leaning and the angle of the stone's lean. I write in my field book where on the top of the stone the measurement was made (e.g. the center, high point, chiseled "x", etc.) and any chisel marks I was able to read. If the marks are difficult to read I use the mirror on my Brunton to reflect sunlight onto the face from different angles. Sometimes the changing shadows on the marks "illuminates" the chiseling. Sometimes, I will revisit the stone early in the morning or late afternoon. When back in the office, I can virtually rotate the stone to an upright position.

I rehabilitate leaning stones by getting out my G-pick and removing the wedge of soil on the uphill side of the stone. Usually, there is a collar of stones around the corner stone so I rotate the stone to fit the uphill side of the stone collar. If, in my opinion the stone is no longer durable (CO standard regarding whether to replace the original) I will replace the stone with a modern monument. However I do not bury the stone. A now retired mineral surveyor told me many moons ago that he used to bury the original stone as a memorial, but stopped that practice because the modern monument would be disturbed if a future surveyor for some reason decides to dig up the original stone. Also, here in Colorado I have noticed that BLM dependent resurveys of mineral surveys no longer bury the original monument. The field notes state that the stone or wood post was placed in the rebuilt stone mound. I appreciate it when a previous surveyor does not bury the original monument so I can look at the original monument. Below are a couple of examples illustrating my point

Here is a photo of a leaning stone before being rehabilitated

And here is a mineral survey bearing rock. The first photo was taken at noon and the second 5 hours later the same day. What a difference the direction of the light source makes.

Posted by: @field-dog

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I was taught that EDM distances less than 100' are not as accurate as a steel tape.

When I was using a Topcon GTS-302 with a CST round prism, I'd agree with that for very short (under 10') distances.  But since I began using a Leica TCRA1102plus and a GeoMax Zoom80 with a Leica GMP-101 prism, I find that the reverse is true.

A prism is mounted on a prism pole and the bubble is centered.  The back of the prism assembly is barely touching something vertical, say a wall or a power pole or a sign post.  Assume the TS is set up such that it is a level shot to the prism.  The measurement obtained is to the center of the prism assembly where the threads secure the pole, thus the measurement of a common shot.  The wall, pole or sign is at a longer measurement based on the geometry of the prism/prism pole assembly.

Posted by: @holy-cow

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The wall, pole or sign is at a longer measurement based on the geometry of the prism/prism pole assembly.

That's the reason data collector software includes offset measurement functions.  The calculated position of the desired object is calculated from the total station measurement combined with the measured offset (in/out and/or left/right).

When I started out in the late 80', my first chief would have us chain anything critical within 25 to 50 feet of the instrument.  I'm not sure I could pull a chain 50 feet and be as precise as a modern EDM.  Okay, it can be done but would take a calibrated chain, tensioners and a second person let alone the time on my knees.

As for prism shots to building corners, before the AP20, I would lean the prism up against the corner and apply a horizontal offset.  Back in the day, I would place the prism against the corner and the gunner would shoot for distance then turn to the corner and record.  That is still how I take reflectorless shots.

@gene-kooper Gene, love the photo of the leaning stone in a meadow with the mountains in the background. Sigh, those were the good old days.

So Gene, when you rotate those stones back in to make them upright, don't you change the orientation of the chiseled lines indicating the direction and distance of other corners? 🙂

Also, GNSS'ing building corners is not anywhere near accurate. Gigantic obstruction and possible multipath.

Finally, and this is not for Gene, what was the accuracy of those stones in the first place? Talking about a tenth or even a half foot would make a BLM surveyor smile. Consider how they set those stones.

Just my two cents--oops, nickels since we no longer have cents....

At the time those stones were set, no one was worried about the length of a flea's penis.  The entirety of the stone was the monument.  Being able to find the stone was what mattered.  Modern technology and weak minds insist we must define which atom within the stone is the TRUE AND ONLY CORRECT CORNER.

Surveyors, engineers and scientists need to get over themselves and black box displays of 18 significant digits to the right of the decimal point.  We are not calculating trajectories for interplanetary space travel where a positional error during a period of velocity approaching the speed of light might doom the entire mission.  We are looking at a large misshapen object and are thrilled that it has been found.  Finding it is the entire goal.

The stone may have been moved by natural forces between the time it was set in place and its discovery by a modern surveyor.  But, other stones nearby, by which it's relative position is to be compared, may or may not have been impacted identically.  Does that automatically make any of them wrong?

@bruce-small I'm not sure I'd call that particular spot a "meadow." The stone is on the east side of Mt. Bross and the NAVD88 elevation of the top of the rehabilitated stone is 13,163.5 ft.

The mountain in the background is Mt. Silverheels, which was named after a young dance hall girl in the Buckskin Joe mining camp northwest of Alma, Colorado. The miners established the first mining district laws and regulations for the Kansas Territory in September 1859. Since you are an avid reader, see Nolie Mumey’s 1961 book, "Early Mining Laws of Buckskin Joe: 1859."

@holy-cow You are incorrect in saying the stone may have moved. The survey was started on November 20, 1891 and completed on January 19, 1892! The stone is leaning downhill due to geologic mass wasting processes, particularly frost heave and soil creep. These geologic processes are supported by my photo. The stone mound is an original accessory and I properly rehabilitated the stone to an upright position within the mound.

If you want to argue against my position, then I suggest that your follow-up response begin by answering why U.S. Deputy Mineral Surveyor, W.H. Powless would purposely set it leaning down the fall line of the slope!

@gene-kooper   Gene, you are amazing.  You clearly have a great set of lungs and general stamina.  Most 40 year-old men could not keep up with you on a typical day of mineral surveying.  Most of those who could, would not be comfortable indoors digging through the historical record searches you must make to understand where and how to make your search for THE stone amongst thousands of other stones.

I recall you once had Dave Karoly (another great participant here) spend some time with you.  Even though he was accustomed to the rough terrain from his experience following forest fires in California, he couldn't keep up with you.

Posted by: @mountainhermit

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So Gene, when you rotate those stones back in to make them upright, don't you change the orientation of the chiseled lines indicating the direction and distance of other corners? 🙂

I'm sorry, but I have no idea of what you are asking. See also my post to HC above. In my professional opinion the stone was originally established in an upright position, period. I merely rehabilitated it to its original position. I would think with your nom de plume that you would have noticed this in your work. I can see why a surveyor from southeast Kansas might not have experience with stones leaning significantly down the fall line of a mountain slope.

As for your assertion that GNSS instruments cannot accurately locate building corners, my experience (esp. in Central City) shows otherwise. Your position was correct for GPS and early GPS + GLONASS instruments. I do monitor the number of satellites from the four constellations, take multiple observations at different times and compare them to the results of the terrestrial photogrammetry and the MS60 + AP20 pole. 

I think the better question that everyone has avoided until now is why would a surveyor use a building corner tie when accuracy is warranted. If the surveyor is concerned with accuracy then set one or more reference monuments. I have been reestablishing the 1880 Central City Triangulation Survey, which has 80 triangulation stations. Twenty-six of those are building corners. Below are photos of Tri-Station No. 8, which is described as the "southwest corner of a brick powder house." So where exactly is the building corner? I just completed a least squares adjustment of the triangulation survey and I did not include one tri-station building corner in the analysis. I reserved the building corner tri-stations to act as checks to the adjustment. The residual for Tri-Station No. 8 is 0.2 feet. Not bad for an 1880 survey!

@holy-cow HeHe. Being a septuagenarian, I'm not so frisky these days. My work day has been reduced to 3-4 hours, which is usually followed by a day of rest for my arthritic knees. That is why I invested in my Leica instruments. Coupled with my research, I try not to revisit corners other than when I decide I need multiple occupations at different times so I sleep better at night.

@gene-kooper    Based on a photo taken by my cousin in recent days of about 30 elk parading through her yard about 20 miles west of Woodland Park, there has been plenty of snow on site to make rock hunting a challenge.  Roughly how close to your initial search area are you able to get before setting out on foot?  Both vertically and horizontally.

@holy-cow Borrowing one of Loyal's favorite phrases....it depends.

After conducting the basic research, I begin by preparing drawings of each mineral survey that is part of the project. I plot up everything including streams, roads, ridge lines, and mining improvements. I then do a preliminary fit of the claims using the connections in the field notes. After that I download aerial photography for the area, usually multiple years of the Dept. of Agriculture's NAIP (National Agriculture Imagery Program) imagery. The main reason I use NAIP imagery is that it is free. 

If the imagery is above timberline, I do a best fit of the mining improvements listed in the official field notes to the mining scars on the aerial. For projects below timberline, the mining scars are not as visible and/or obscured by tree shadows. In those cases, I try to fit the drawings to any geographic features shown on the plat(s). For projects above timberline I can usually register the drawing to the aerial within 25 feet.

I then take the print and the field notes to the field and look for rocks that stick out of the ground similar to what a stone monument might look like. I follow Steve Parrish's advice and walk a spiral out from the positions plotted on the aerial. I also look for the mining improvements. When I run into problems, I ask my wife to join me. She is very good at finding the cherished stones amongst all the rocks.

This is of course an iterative process. If I find any corners, I go back to the office and adjust the drawing to fit with the found corners and go back out. As for which corners I search for first, I begin by looking for corners with original accessories, such as bearing rocks and bearing trees. Original accessories are important because they validate that the corner stone has not been moved by others. That is something that Paul Reid was very insistent about, "because corners can be moved!" He was also fond of telling others to get their butts back in the field when they failed to find it the first, or second, or third time!

An aside. If I find original accessories (that includes stone collars) and the stone has been disturbed, I reestablish the stone based solely upon the accessories. I do not utilize ties to other mineral survey corners because recovering the original accessories means that the corner is extant. The use of other mineral survey corners to reestablish a corner is for situations where the corner is lost or destroyed. 

@gene-kooper   You have invoked both Loyal Olson and Pablo in a short message.  They both have been great contributors to earlier versions of this site.