Surveying (Geomatics) involving allowable misclosures

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Discussion Overview

The discussion revolves around the computation of permissible misclosure for a 15-kilometer loop of third order leveling in surveying (geomatics). Participants explore the calculations involved, the significance of allowable misclosure, and the handling of measurement errors in surveying practices.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • A participant seeks verification of their calculation for permissible misclosure, noting a discrepancy in units between their computed answer and what was recorded in class.
  • Another participant questions the rationale behind allowing misclosure in surveying and discusses factors affecting measurement accuracy, such as instrument errors and atmospheric conditions.
  • A response emphasizes the importance of unit specification in calculations, suggesting that dimensional analysis is necessary to understand the factor of 1000 discrepancy noted by the original poster.
  • One participant provides a specific formula for third order leveling misclosure, stating that it should not exceed 12 times the square root of the distance in kilometers, confirming the computed value for 15 kilometers as 46.5 mm.
  • A later reply references the same misclosure formula, reiterating its relevance even in older discussions.

Areas of Agreement / Disagreement

Participants express differing views on the handling of misclosure and the importance of unit consistency in calculations. There is no clear consensus on the original poster's calculation, as some participants provide corrections and clarifications while others focus on broader concepts.

Contextual Notes

Participants highlight the need for clarity regarding units in calculations, indicating that mixed units may lead to significant errors. The discussion also reflects on the conditions under which misclosure is acceptable and the implications of measurement errors in surveying.

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Homework Statement


Compute the following permissible misclosure for the following line of level.
a 15kilometer loop of third order level.


Homework Equations


C=msqrt(K)
where K is the distance and M is a constant


The Attempt at a Solution


For the most part I just need to verify if I copied my answer correctly because when I calculate this, I get 46475MM as my answer, but what I have written down is 46.5MM
I can see the similarity in the answer, off by a factor of 1000, so could anyone please confirm if my answer is correct and the one I have written down from class just has the wrong units? If I did do it wrong, where did I go wrong?

I plugged in 12 for m since it's a third order level and plugged in 15KM for K, or 15,000,000MM.
 
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why are surveyors are permitted to have allowable mis close and how they deal with it?
 
Abdul Faiyad said:
why are surveyors are permitted to have allowable mis close and how they deal with it?
@ Abdul Faiyad. Welcome to PF.
The survey makes accurate measurements that are affected by many things such as instrument errors, atmospheric refraction, variation of the vertical due to local mass distribution and Earth tides. It is only when the survey is closed that the closure error is known. If the error is too big, the survey must be checked or repeated. If the error is acceptable, it can then be partitioned and distributed to the intermediate stations based on the length of the sights between stations.
 
@ mathnoobie.
You have not specified what units you are required to use with C = m * Sqrt( k )
Dimensional analysis requires the units of m to be Sqrt( length ).
Mixed multipliers will explain a factor of 1000.
Where should you use metres or mm ?
 
Numbers are meaningless without units.
Third Order: Differential levelling. Misclosure in mm is not to exceed 12 * √ km.
For 15 km you have 12 * √15 = 46.5 mm
 
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mathnoobie was last seen:
Aug 18, 2013:
Baluncore said:
Third Order: Differential levelling. Misclosure in mm is not to exceed 12 * √ km.
Useful information, even for a "necropost."
 

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