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Typical Survey Control Monument Network Design


gurubob

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once new and existing monument locations are finalized, existing NGS HARN stations and bench marks are selected as project control. Control is selected in a configuration optimized for both horizontal and vertical support of the GPS network(s) and in accordance with the FGCC guidlines with sufficient redundancy to allow for quality control evaluation and blunder detection.

at least one GPS session baseline should be directly observed between each station azimuth pair. this results in uniform coordinate quality on all survey stations, an overall stronger GPS network and fewer total GPS observations. when existing NGS bench marks can not be directly occupied, a temporary eccentric point should be set at a nearby inhabitable location. conventional differential leveling techniques can be used to transfer an elevation from the bench mark to the eccentric point.

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Bob

Having seen that this message has gotten no responses, I would offer this advice. While your statements are true, its fairly difficult for most people here, myself included, to see how they relate to geocaching. I have found that most folks here are not really too excited about all the technical aspects of geodetic surveying, but rather are in this for personal fun and adventure, so using too much technical jargon is probably a non-starter. Its also likely that a number of people were alienated by the strident tone of your first message and thus have decided to ignore your input, which is a shame, since you obviously have a lot of knowledge to share. There are only a handful of surveyors, who have identified themselves as such, that contribute here on even an occasional basis, and I have been hoping more, like yourself, would step up and be heard, so this is disappointing to me, and the reason for my response. So lets try to give the public a positive impression of our profession, by demonstrating that we appreciate their interest in surveying, providing helpful advice and answers to questions when we can, and gradually enlightening them in the process, rather than reinforcing the currently prevalent public image of surveyors as technical mavens, engrossed in mathematics and technology and out of touch with reality.

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Lest the silence be misinterpreted, I was happy to see you post again, Gurubob. We've learned a lot from survey tech, and I expect we can learn a lot from you, too (also you might take some of the load off survey tech that we put upon him and the other pros!).

 

So my silence wasn't a cold shoulder (I can't speak for everyone, but I think most of us can relate to your concern for the integrety of the BM system, and I hope our misunderstanding of where each other was coming from is behind us). But your post did go pretty well over my head. I was waiting to see if anyone else responded to clarify.

 

Sooo...would you care to translate that into layman's terms? Enquiring minds want to know! icon_confused.gificon_smile.gif

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quote:
Originally posted by gurubob:

once new and existing monument locations are finalized, existing NGS HARN stations and bench marks are selected as project control. Control is selected in a configuration optimized for both horizontal and vertical support of the GPS network(s) and in accordance with the FGCC guidlines with sufficient redundancy to allow for quality control evaluation and blunder detection.

at least one GPS session baseline should be directly observed between each station azimuth pair. this results in uniform coordinate quality on all survey stations, an overall stronger GPS network and fewer total GPS observations. when existing NGS bench marks can not be directly occupied, a temporary eccentric point should be set at a nearby inhabitable location. conventional differential leveling techniques can be used to transfer an elevation from the bench mark to the eccentric point.


 

This is just a stab at interpeting the above. As I am not a profesional surveyor by trade, I hope that I will learn something from this as well.

 

Surveying projects require a set of points to provide accurate results of that project. The set of points selected are considered the project control points. Only new or existing monument locations are acceptable as control points. Additionally it is preferable that thes points have clear visibility into the gps network. (From doing ngs submissions my understanding is that this means clear sight to the sky in all directions 15 degrees above the horizon, and that the point be available to a surveyor to emplace the gps equipment to make such a reading. Flagpolls, spires and most watertowers are considered unsuitable.)

 

It is also preferable that these points be reasonably close to the project work area, to reduce the number of gps reading required to complete the project.

 

If for some reason a NGS benchmark is not available to the surveyor that is suitable for the project, a temporary reference point may be created close project area. To make this temporary reference point a surveyor will first calibrate the gps unit by going to one of the NGS marks and then go to the temporary reference point to take a comparison reading and based upon the difference between those two readings provide a differential reading for the temporary reference point.

 

My presumption is that this temporary mark must be established before or at the begining of whatever project is being undertaken.

 

Ok professionals, how did I do?

 

-Rusty

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quote:

Closer to the edge posted November 03, 2002 09:25 PM

--------------------------------------------------------------------------------

Glad you're here, Gurubob

 

Lest the silence be misinterpreted, I was happy to see you post again, Gurubob. We've learned a lot from survey tech, and I expect we can learn a lot from you, too (also you might take some of the load off survey tech that we put upon him and the other pros!).

 

So my silence wasn't a cold shoulder (I can't speak for everyone, but I think most of us can relate to your concern for the integrety of the BM system, and I hope our misunderstanding of where each other was coming from is behind us). But your post did go pretty well over my head. I was waiting to see if anyone else responded to clarify.

 

Sooo...would you care to translate that into layman's terms? Enquiring minds want to know!


 

Well said!

Gurubob, I'm sorry if my prior response to your 1st post seemed hostile to you. I was not venting at YOU. Its just that you addressed a point which has been bothering me, and I threw my response out to see how the professionals, as well as other "hunters" felt about coming across so many destroyed marks that were obviously removed by, and not reported by, professionals.

 

Anyway, I hope you continue to grace us with your insights and experience. I look forward to learning more about "the system" from you, as I have from surveytech's posts.

 

Art

 

www.yankeetoys.org

www.BudBuilt.com

http://www.ttora-ne.mainpage.net/

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In this thread of discussing relationships of survey points, I'd like to re-ask a question I've asked before but didn't 'get' the answer.

 

Why is an azimuth mark set? What use is made of it?

 

I can see that, between the main station and the aziumth station, there is established an accurate bearing that isn't dependent on magnetic readings. However, I'd like to know what the uses are of such a bearing.

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BDT

The main reason the concept of azimuth marks was developed is due to the fact that most triangulation stations are very far apart and they are usually not intervisible from the ground. So, in order to save local surveyors from having to go to all the trouble of using towers to see from station to station, an azimuth mark was set for each station, at a spot convenient for local visibility. The local surveyor can then set up a surveying instrument on the station and sight down to the azimuth mark and immediately orient his work to the network. You are right that the bearing system of directions, while mathematically identical to magnetic compass directions, is actually an entirely different system, free of magnetic fluctuation, based on astronomic north, as determined by astronomic observations on Polaris and/or the other observable stars. You may also notice that bearing/azimuth directions between points on the NGS datasheets are given in both absolute and grid form. Each portion of each state has its own grid system, based on either Lambert or Mercator projection, used to minimize the distortion introduced by the curvature of the earth. The difference between absolute azimuth and grid azimuth at any given point is known as Theta, which is a function of how far the point is from the center of the projection area. The significance of this, of course, is that surveyors typically work on a surface that is treated as a plane, rather than an arc, so the Theta angle is used to convert from absolute directions to grid directions. Pretty technical stuff, but you asked for it.

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Thanks, gurubob - that explains alot. I think your post, without some sort of context (your friends initial question) canme across as simply some factual data you were presenting to those who read this forum.

 

I'll look closer at the icons used by those posting messages, but I would also recommend folks making posts include contextual information to make their posts more clear to those reading them.

 

-

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quote:
Originally posted by gurubob:

I posted this POB article to answer a friends question. I thought the little picture of the printed paper with a thumb tack would make that clear. This is a description of a survey control network that would be suitable to establish NGS monumentation.


 

Actually you are right and wrong. But then we all are. This board is to discuss the experience of benchmarking and share knowledge. There are several recomended practices to take when posting material to this board.

 

Presuming that you are a professional surveyor, and from the three posts you have made, only one shows some indication of that, and it is denegrating as it is, you have called that into question even in this topic. As a professional you understand that there are people who will be currious about your profession who may have no interest in persuing it as a profession of their own.

 

There are three ways of talking to these people. One you can play the high and mighty. Two you can patronize. Three you can try to find a common ground that improves the view others have of your profession. One and two are not mutually exclusive, though three is completely separate from the others.

 

I am a professional in a completely different field from suveying. People in my profession call upon surveyors for several different projects. Why? Because for those projects we have legal obligations that require us to confirm prior to the start of those projects, during the project itself, and at the conclusion of our projects that what we are doing falls within the regulated boundries of that project.

 

Is it possible that I would be able to do that which we call upon suveyors to do? Sure. However it would not be legal, and I think that to do it right I would spend a long time in preparation.

 

That said. Your post at the begining of this thread could very easily have been written at a level where people who are currious about the subject could understand what was being said. Alternatively you could have provided pointers to resources providing substantially similar information as makaio has demonstrated.

 

My read of your original post in this thread is that you considered it to be beneath yourself to provide an explanation of how to extend a GPS network at a level that would make sense to the general public.

 

quote:
and in accordance with the FGCC guidlines with sufficient redundancy to allow for quality control

 

is effectively long hand for saying "we follow published standard rules that lay out how to provide reliable work"

 

I am reasonably sure that your buddy did not need the information you posted here in the form you presented. Either the information would have been better sent to him directly, or should have been re-written in a less technical form.

 

Even the form I attempted to re-write your posting in, is outside the scope of understanding of many casual readers here. I seriously suspect that if I were to copy and paste it into one of the other forums on this set of boards that it would be above the heads of a large percentage of the readers.

 

Again presuming that you are a professional surveyor, most of use here would appreciate finding out about your positive and negative experiences working with benchmarks while surveying. Especially when they are directly related to one of the topics under discussion.

 

Then again, I am long winded and I am sure that some will think I am going easy on reviewing your posts.

 

We are a community here. We welcome professionals, amatures and visitors. We are currious about many aspects of surveying, for many different reasons. I happen to be currious about how different experties work together to make the collection of activities that is going on around us function as a whole.

 

I won't speak specifically for anyone else here.

 

-Rusty

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quote:
Originally posted by gurubob:

I din't mean to insult anyone. I found a good answer to a hard question to answer.


 

I think the point was that this isn't Jeopardy. You spit out an answer and nobody here even knew what the question was. Usually a thread starts with a question and then gets answers. You started with the answer and we are guessing the question.

 

"We will add your biological and technological distinctiveness to our own. Your culture will adapt to service us. Resistance is futile. We are the Borg."

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