Chapter-6 Tacheometry
Surveying I (3-1-4)
Content of the course
Chapter-6 Tacheometry (5 hr)
Introduction, Uses and Importance
Principles of Optical Distance Measurement
Systems of Tacheometry- Stadia System and
Tangential System
Distance measurement using vertical staff
Instruction on field works
Carries about 10 to 15 marks in final
examination question.
Introduction
• Tacheometry:
- Tacheometry is a system of rapid surveying, by which relative
positions of points, both horizontal and vertical, on earth
surface are determined without chaining or taping.
- It is a branch of surveying in which the horizontal and vertical
distances of points are obtained by optical means as
opposed to the slower process of measurements by tape or
chain.
- This method is very rapid and convenient.
- It is best adopted in areas such as steep and broken grounds,
deep ravines, stretches of water or swamp and so on, where
chaining and taping is difficult or impossible.
Introduction
• Tacheometry:
- The primary objective of Tacheometry is the
preparation of contoured maps or plans requiring
both horizontal and vertical control.
- Also, on surveys of higher accuracy, it provides a
check in distance measured with the tape.
Introduction
• Tachometer:
- A Tachometer is essentially a transit
theodolite, fitted with stadia diaphragm.
- The stadia diaphragm consists of two
stadia hairs at equal distances, one above
and other below the horizontal hair of the
cross-hair.
- Essential Characteristics of Tachometer:
• Value of multiplying constant should be 100
• Value of additive constant should be 0.
• Telescope should be fitted with anallatic lens.
• Magnification of telescope should be 20 - 80
diameters, magnifying power of eye piece is
kept high.
Uses and Importance
• Preparation of topographic maps which require both
elevations and horizontal distances.
• Survey work in difficult terrain where direct
methods are inconvenient.
• Detail filling
• Reconnaissance surveys for highways, railways, etc.
• Checking of already measured distances.
• Hydrographic surveys and
• Establishment of secondary control.
Classification of Different Methods
of Tacheometry
Tacheometry
Stadia Tangential
Method Method
Fixed Hair Movable
Method Hair Method
Principle Of Optical Distance Measurement
- Stadia Method
FIXED HAIR METHOD
• This is a method of finding distance and elevation of staff
from Tachometer
• Different Formulas are used in finding Distance for
different Cases.
• Cases:
I. When line of sight is horizontal and staff is held
vertically.
II. When line of sight is inclined and staff is held
vertically
III. When Line of Sight is inclined and staff is held
normal to line of sight.
CASE I: Line of sight is horizontal and staff Vertical
CASE I: Line of sight is horizontal and staff Vertical
CASE I: Line of sight is horizontal and staff Vertical
From the earlier equation, we can see two different
constant values exists in equation.
K = Multiplication Constant = (f/i)
C= Additive Constant = (f+d)
In Modern Tachometer, fitted with anallatic lens, The
value of Multiplication Constant is K = 100, and that of
Additive Constant is C= 0
Thus, For Horizontal sight we have;
Horizontal Distance (D) = 100 * S
CASE II: Line of sight is Inclined and staff Vertical
CASE II: Line of sight is Inclined and staff Vertical
Horizontal Distance (D):
D = L*CosƟ
D = (K * SCosƟ + C) CosƟ
D = KSCos2Ɵ + CCosƟ
Verical Distance (V):
V = L * Sin Ɵ
V= KSCosƟSinƟ + CSinƟ
V = ½ KS Sin2Ɵ + CSinƟ
RL of P=
RL of O + HI + V -h
CASE III: Line of sight is Inclined and staff Normal
to line of sight
CASE III: Line of sight is Inclined and staff Normal
to line of sight
RL of P= RL of O + HI + V -hCosƟ
MOVABLE HAIR METHOD
• In this Method the staff intercept is kept Constant,
But the distance between the stadia hairs is variable.
• Such theodolite is known as Subtense theodolite
• The diaphragm consists of central wire fixed with axis
of telescope; Upper and lower stadia hairs can be
moved by micrometer screws in a vertical plane.
• The distance by which the stadia wires are moved is
measured according to number of turns of the
micrometer screws.
MOVABLE HAIR METHOD
TANGENTIAL METHOD
TANGENTIAL METHOD
TANGENTIAL METHOD
TANGENTIAL METHOD
Chapter C. Subtense Bar (jerrymahun.com)
Know more @ this link
Chapter C. Subtense Bar
(jerrymahun.com)
