Tacheometric Survey 2t255f

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Tacheometric survey  What is it?

Introduction

  It’s a branch of survey which deals with the study of measurement of vertical and horizontal distances using a Tacheometer.

What is a Tacheometer?

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Tacheometer

 No rocket science!  Ordinary transit theodolite  Fixed with stadia diaphragm and anallatic lens.  The job of the lens is to make the additive constant equal to zero.

Constants   f/i=multiplicative constant  (f+d)= additive constant  x=angle between line of sight and the middle stadia hair  f=focal length of lens  i=stadia intercept  Normally the values of multiplicative constant is 100 and the additive constant is equal to zero.

Principle of Tacheometry   The principle of Tacheometry is based on the property of isosceles triangles. Where the ratio between height and base is always constant.

D1/S1=D2/S2=D3.S3

=f/i

Where it can be used   When obstacles like river, broken ground, stretches of water come in way then it provides a speedy and accurate measurement.  Places where terrain is mountainous or undulated where the measurement of horizontal and vertical distances is difficult, slow and inaccurate.

Advantages  It is used to prepare contour maps It is used for hydrographic survey It saves time and money It also reduces the error when compared with chaining.  Used for road and rail surveying.    

How to use it ?   The person taking the reading should measure the upper and lower stadia readings and then make the calculations.

Formulations and calculations

 For measurement on a level terrain the formula is D= [(f/i)*s]+(f+d) RL=HI of instrument-h Where D= distance f=focal length i=stadia intercept s=staff intercept d=distance between vertical axis and center of lens h=central hair reading HI=height of instrument  

Case I   If staff is at an at an elevation to the Tacheometer.  The staff if to be vertical D= (f/i)*s*(cos(x))2 +(f+d)*cos(x) V= [(f/i)*s*sin(2x)*.5]+(f+d)*sin(x) Reduced Level=RL of axis of instrument+V-h D=horizontal distance V=vertical distance f=focal length i=stadia intercept d=distance between vertical axis and lens h=central height reading   

Case II   When Tacheometer is at an elevation to the staff  D=[(f/i)*S*(Cos x)2+(f+d)*Cos x]  V=[(f/i)*(S*Sin 2x)/2]+(f+d)*Sin x]  RL=RL of instrument axis-V-h h=height of staff D=horizontal distance V=vertical distance f=focal length i=stadia intercept x=angle of depression h=central hair reading

Case III   Line of sight inclined but staff normal to it. Staff is at an elevation(+ive elevation) to the Tacheometer D=(f/i)*s*cos(x)+(f+d)*cos(x)+h*sin(x) V=(f/i)*s*sin(x)+(f+d)*sin(x) RL=RL of instrument axis+V-h*sin(x) D= horizontal distance V= vertical distance s= staff intercept i= stadia intercept x= angle of depression h=height of staff

Case IV   Line of sight inclined but staff normal to it. Tacheometer is at an elevation to the staff.  D=(f/i)*s*cos(x)+(f+d)*cos(x)-h*sin(x)  V=(f/i)*s*sin(x)=(f+d)sin(x)  RL=RL of instrument axis–V-h*cos(x) D= horizontal distance V=vertical distance x=angle of depression i=stadia intercept s=staff intercept f=focal legth

references   Wikipedia.org  N.N Basak This presentation was brought to you by 1. 330-civ-2013 2. 331-civ-2013 3. 332-civ-2013 4. 333-civ-2013

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