Tuesday, January 7, 2014

Surveying notes for GATE and PSUs exams. - Part 11

Hello there, 
The following facts are taken from many references, mainly from the book titled "Civil Engineering objectives" by S P Gupta and S P Gupta.
  • Bowditch method has used the assumptions:  Errors in linear measurements are proportional to under root of L.; Correction to latitude or departure of any side = Total error in L(or D) * (Length of that side/ Perimeter of traverse).
  • To determine the length of a bridge proposed to be built across a wide river, the triangulation method of surveying will be preferred over tacheometry, chain surveying.
  • Heliograph is a type of sun signal used in triangulation work.
  • A 100 m tape is held 1 m out of line. The true length will be 99.995 m
  • When the line of collimation is not perpendicular to the horizontal axis taking face-left and face-right observations reduces the error.
  • It is not necessary to do the exact centering of plane table to do the small scale surveys.
  • Saddle line is also known as ridge line or valley line.
  • Line of drainage basin is the line which passes through ridges and saddles setting up a domain.
  • Longitude of a place is measured by wireless time signal and transportation of chronometers.
  • In tilting level the vertical axis is not perpendicular to the line of collimation.
  • Inverted staff readings are taken for the points above the line of collimation.
  • Reciprocal levelling eliminates the error due to inclined line of collimation also.
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