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Newest Benchmark


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What was the newest benchmark you have ever found?


Did you ever help set one? An NGS crew was in town today and guess who got to help out :laughing::lol::D Being a Geomatics(Surveying) student has its bonus'. This was a very rare occurance as there is actually only one crew currently doing this work for the whole US due to budgetary reasons.


I am beside myself with joy :lol:







Edited by ralann
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That must have been a great thrill! It would be fun for me to just meet any of the other people who frequent this forum, to talk about this hobby, let alone meet the NGS crew.....


I was really excited when we got to talk to a couple of surveyors that had just placed their stand to occupy one mark that we pass by often. We had a 'Locationless Cache' that we wanted to do, it required you to find a surveyor's tripod over a mark, with who placed it. So, we had to stop and ask them some questions. That was a real interesting cache for us...it is archived now.


How did you know they were going to be there and setting a mark? Did you just drive by or did your school tell you?


But, of course they let you "dig that hole", right? :sad:


Just how deep is that hole and how do they place the rod into it? Tell us all of the details, please.



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How did you know they were going to be there and setting a mark? Did you just drive by or did your school tell you?

The buzz in our department was very high about the crew arriving. We had a couple months worth of notice.

But, of course they let you "dig that hole", right? :ph34r:

Actually the grounds crew used an auger to bore a 2ish foot deep outer hole and about anothen 2 foot of smaller hole in the middle.

Just how deep is that hole and how do they place the rod into it? Tell us all of the details, please.

The rod is threaded is 4foot sections and drive in using basicly a jackhammer device that instead of having a point has a slot/hole for the rod to slip into. We drove the rod 32feet in till it hit bedrock and refused to travel farther. When the rod was in they use a hydrolic cutter and a grinder to dress up the end. The process is fairly simple but if you have any specific Q's just ask and I'll try to answer them.

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No offense Stripemark, but I think it is a shame that the original cross was destroyed by the mounting of a disk in its place. I always feel somewhat cheated when I find a mark that was set a long time ago but had a disk set in its place. It is as if history has been stolen or changed. Yes, I know that a disk may be more accurate than the chisel mark, as well as easier to locate, but that doesn't change how I feel about it!

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I agree. Not only have I never seen a mark set, I have never even seen a mark being USED. And I have searched for 1,200 marks. The benchmark gods are against me in that respect.

I must be a favored mark hunter as I have seen several marks used.


What kind of mark hunter are you when you actually use them? :( This is GT2079 that I found (and used) on May 3rd, 2006.




Ralann - the jackhammer/grinder process you describe is how I occasionally have to set property corners and section corners in the valley hardpan. (Hardpan is like naturally occuring concrete.) Of course, I'm only setting them about 3'-5' down - much easier than 30+ feet. And, along with everyone else, I'll also have to admit a bit of envy at your opportunity to help the crew set the mark. It is a rare opportunity, to say the least, even for surveyors.


MLoser - next time I know I'll be using an established and published NGS mark, I'll let you know and you can tag along.


- Kewaneh

Edited by Kewaneh & Shark
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A week or so ago I spotted a tripod with a survey-grade GPS gear on it, cabled to what appeared to be a radio transmitter for off-site data collection. It was at Washington-Lee High School in Arlington, Virginia (alma mater of Sandra Bullock, Warren Beatty and Shirley MacLaine, for what that's worth), where they have just broken ground for construction of a new school building.


There was only a temporary point beneath the tripod — a spike, I think— not a disk. There are at least two county benchmarks within a couple of blocks' radium (horiz and vert control, I think). I can't imagine that they would be too far away to tie into for the project. So if my assumption is correct (that a temporary point was being established), why was it being done with new GPS observations, rather than tieing into the existing network. Is it cheaper that way? Or would an addition, closer fix be qualitatively better?



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My first thought is that the point was established as an eccetric to an existing mark that could not be easily used for GPS. There are some permanant marks set up that were used that way, like AB6472 or AB6504.

Hmmm. Maybe. Here's a map of the area. Local benchmarks indicated in green; location of high school in blue; position of GPS unit seen by me in red.



Some, and possibly all, of the nearby local marks may be unsuitable for GPS observations. But they appear to be located to a high degree of accuracy (or, at least, precision). BN009, for example, is given to SIX decimal places of seconds.



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A week or so ago I spotted a tripod with a survey-grade GPS gear on it, cabled to what appeared to be a radio transmitter for off-site data collection.


That sounds like a RTK (real time kinematic) setup. That is thier base station broadcasting position corrections to other units (called rovers). With that method, the rovers are getting CM level accuracy. You can have as many rovers as you want. We at times ran with 4 rovers and 2 base stations going. Collect data from one base, switch channels and shoot point from 2nd base and the receiver would compare the rover positions to what ever accuracy you preset and average (mean) the point position. i.e. Real time solution to the new point, no more comps to do provided the base stations were on the final datum you needed for your project, weather it be state plane, local grid, project datum or assumed.


Anytime you see an antenna that is RTK. You can also use cell phones, its more costly but your range is farther than with radio. The radios don't cost you for air time but depending on terrain limited to only a mile or so. Laws limits radio power allowable.


RTK is a process where GPS signal corrections are transmitted in real time from a reference receiver at a known location to one or more remote rover receivers. The use of an RTK capable GPS system can compensate for atmospheric delay, orbital errors and other variables in GPS geometry, increasing positioning accuracy up to within a centimeter. Used by engineers, topographers, surveyors and other professionals, RTK is a technique employed in applications where precision is paramount. RTK is used, not only as a precision positioning instrument, but also as a core for navigation systems or automatic machine guidance, in applications such as civil engineering and dredging. It provides advantages over other traditional positioning and tracking methods, increasing productivity and accuracy.


Using the code phase of GPS signals, as well as the carrier phase, which delivers the most accurate GPS information, RTK provides differential corrections to produce the most precise GPS positioning.


The RTK process begins with a preliminary ambiguity resolution. This is a crucial aspect of any kinematic system, particularly in real-time where the velocity of a rover receiver should not degrade either the achievable performance or the system's overall reliability.

Edited by Z15
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