Help Distributing Error In A Level Survey

[MatthewMansfield]

Hello all

I was wondering if there was anyone out there who could help explain how to distribute a misclosure error in a level survey.

I carried out a survey of a road. i used several TBMs and several change points. When i closed the survey i flew back using the same change points and ended back the survey on my original TBM.

My first TBM reduce level value was 10000, my second TBM reduce level value was 9378 and 3rd TBM was 8948.

When I fly back to close the survey I re-survey TBM3 and I got a reduce level of 8948, but when I re-survey TBM 2 I got a reduce level of 9379 (a difference of 1mm from the previous value) and my final TBM value I get a reduce level of 10005 a difference of 5.

How do you distribute the error, I simply do not understand the process of distributing the error. If someone could explain how you would distribute the error then that would help a great deal.

The issue i have is that i do not know over which change points i made the error (assuming that the error was as a result if misreading).

Thanks

Thanks in advance

 

[dicksewerrat]

Do it again using new points.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[miningman]

Many years ago when at university, we were given specific training in exactly this type of problem. I can just about remember how to close / distribute angular closing errors but this would be of zero use to you. Surely a good survey handbook or experienced land surveyor could provide the answers.

 

[MiketheEngineer]

You are off by 1 mm - 5 mm or about.040 to .200 inches???

Does anybody really care??

 

[Hoaokapohaku]

I'd answer Mike's question first. It probably doesn't matter. Although, if a contractor uses these points as references for a modern sub-millimeter GIS system for grade control on his equipment, elevation breaks between reference points can drive a guy nuts.

This is just a common sense approach, not "the method" for distributing leveling error, but the differences between TBM's 2 and 3 match going both ways within a millimeter. Assuming 1 millimeter is close enough, it's safe to say there there is no significant error in the difference between those two points. Therefore, all the significant the error is in the difference between TBM1 and TBM2. Given that the elevation of TBM1 is 10000 even, I'm taking that as an assumed elevation that cannot be in error since is your starting assumption. Therefore, the entire error must be in the elevation of TBM2. I would re-verify the elevation of TBM2, and adjust the elevation of TBM3 accordingly to maintain the elevation difference between TBMs 2 & 3 as established by the first survey.

 

[Hoaokapohaku]

I should have asked this first, but what kind of equipment are you using for this survey?