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Hello everyone! 

I'm a land surveying student from Denmark and I'm currently writing my thesis to conclude my education this summer. 

My thesis is about open/blind polygons while surveying through a closed off area and how to ensure the quality of the points through those methods. I think it might be what is referred to as an "open traverse control network" but I'm not that good with the technical terms in English so I could be wrong. Let me know if it makes sense or not. 

So I made a little questionnaire that I'd very much like some answers to that I hope you guys can provide. 

I am of course contacting people in the firms around my country but perhaps nothing will come of those inquiries and I want to make sure I have enough information to go forward. The thing is that I also have to make an practical experiment in surveying for my thesis. I will try out a few of the methods that I hear about and use the data in the thesis. 

Long story short; I need to know what kind of methods people use ensure the quality of their points while surveying in a tunnel or basement. 

The thesis' question is as follows; "Which methods are used in land surveying to avoid situations with a blind polygon?"

1.: Describe the method which is the most commonly used when surveying in a somewhat linear route in your company. (for example; in a basement or a tunnel) (feel free to use illustrations/links if they help the explanation)

2.: Are you using said method because of the quality of the surveying or because it is more time efficient? 

3.: Which issues the the most typical issues when surveying within a blind polygon and how do you solve these issues? 

4.: How do you ensure the quality of the surveying in the field with your most commonly used method? 

5.: Do you use different instruments, prisms, tripods etc. than you normally would when doing land surveying? 

6.: Which programs do you use to calculate the network, do you do something in different from normal surveying to make it work better? 

Again, I'm not sure if I'm using the correct terminology so if something doesn't make sense, feel free to ask. 

I really would appreciate the help from you guys. Thank you :)

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  • Hi ,
    Please you find herein attached a document which give you an idea about the technique

    Good luck

    • Thank you buddy. That is exactly the kind of stuff I was looking for! :)

  • Forward and backward courses work well, and make sure to double your angles. Multiple shots in direct/reverse will aid in maintaining proper alignment. Efficiency will come with learning the technique. These methods balance out the inherent inaccuracies of a blind polygon/open traverse.
  • Best to run the same linear line of control points back to the beginning storing new coordinates for them as if they were different points in a traverse loop. If you can get two points on either end to tie into with GPS for an additional check, that also helps to confirm accuracy. Least squares adjustments are available with several different kinds of software to assist with calculating corrections for errors in closure for your traverse loop.

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