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Unit 4 :- Chain Surveying (Obstacle in Chaining)

 Obstacle in Chaining Sometimes obstacle in chaining occurs while doing chain surveying. Obstacle in chaining are of three kinds: (a) When chaining is free but vision is obstructed. (b) When chaining is obstructed but vision is free. (c) When chaining an vision are both obstructed.   (a) When chaining is free but vision is obstructed :- Such a program arises when a rising ground or a jungle are present. Here the end station are not intervisible. There may be of two cases: i) 1st Case The end station may be visible from some intermediate point on the rising ground. In this case, reciprocal ranging is done and the chaining is done be the stepping method.   ii) 2nd Case (Random Ranging) The end station are not visible from intermediate point when a jungle are comes across chainline.   Let AB be the actual chain line which can’t be ranged and extended because of interruption by a jungle. Le t the chain line be extended upto R. A point ‘P’ is selected on the chain ...
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Unit 2 :- Accuracy and Errors

Accuracy Accuracy refers to the closeness of a measured value to a standard or known value. It depends on three factors: Precise instrument Precise method Good planning The degree of accuracy in chaining is expressed as a ratio called the chaining ratio. For example, if there is an error of 0.05 meters during the measurement of a total length of 500 meters, the chaining ratio is calculated as follows: \[ = \frac{{0.25 m}}{{500 m}} = \frac{{25 m}}{{50000 m}} = \frac{{1}}{{2000}} \] Some permissible limits of errors: For measurement with a steel band: ±8/1000 In normal conditions with a tested chain: ±8/1000 For rough work: ±8/50  Precision: Precision refers to the closeness of two or more measurements to each other. It is independent of accuracy and is often considered a degree of perfection. Discrepancy: This term represents the difference between two major measured values or quantities. Errors: Errors arise from the difference between a measured value and the actual value. These ...
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