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CiIvil Surveying - Theodolite Surveying

**THEODOLITE
SURVEYING**

1.Define:
Theodolite surveying. What are the uses of a theodolite?

Theodolite surveying is a branch
of surveying, in which the theodolite is accurate instrument used for the
measurement of horizontal angles, vertical angles. It can also be used for
various purposes such as laying off horizontal angles, locating points on a
line, prolonging survey lines, establishing grades, determining differences in
elevation, etc,.

2.
Why a type of theodolite is called a transit theodolite?

A transit theodolite is one is
which the line of sight can be reversed by revolving the telescope through 180^{0}
in the vertical plane.

3.
List the essential parts of a theodolite.

The
telescope, The vertical circle, The index frame (T- frame),

The levelling head, The scale plate (Lower), The
Vernier plate (Upper). The tripod, Plumb bob, The compass, Focusing screws,

The upper and lower clamp and its tangential
screws, Vertical clamp screw, Foot screws. etc,.

4.
Differentiate between the Vernier theodolite and Micrometer theodolite.

In Vernier theodolite the verniers are fitted to
read the angles upto 20”. In Micrometer theodolite
micrometers are fitted to read the angles.

5. List the essential qualities
of a theodolite telescope. The essential parts of the telescope:

(i).Objective
(ii).Eye-piece, (iii). Diaphragm, (iv). Body and focusing device.

The
essential qualities of a theodolite telescope:

(i).
The real image must be formed in front of the eye-piece.

(ii).
The plane of the image must coincide with that of the cross-hairs.

6. What are
the temporary adjustments of the theodolite?

1. Setting
up.

2. Levelling
up.

3. Elimination
of parallax.

(i). Focusing the eye piece. (ii). Focusing the
Objective.

7.List
out the permanent adjustments of Theodolite.

1. Adjustment
of plate level (Plate level test).

2. Adjustment
of line of sight ( Cross- hair test).

3.
Adjustment of horizontal axis.(Spire test).

4. Adjustment
of vertical index frame and altitude bubble.(Vertical arc test).

8. List out
the fundamental lines of Theodolite

1. The
vertical axis

2. The
horizontal axis or trunnion axis

3. The line
of collimation or line of sight.

4.Axis
of plate level.

5. Axis of
altitude level.

9. What is
an anallatic lens? What is the use of an anallatic lens?

It is a special convex lens
fitted between the object glass and eye piece, at a fixed distance from the
object glass, inside the telescope of a tacheometer.

The use of an anallatic lens is
to reduce the additive constant ( C ) to zero. Tacheometric equation, D = Ks +
C. Where,

D = horizontal distance between the staff and the
instrument station. S = staff intercept

K = multiplying constant. C = additive constant.

10. Name the two methods of measuring horizontal
angles using a thedolite. When each method is advantageously used?

The
two methods: (i). Repetition method.

(ii).
Reiteration method (Direct method).

The method of repetition is preferred for the
measurement of a single angle. The method of reiteration is preferred in triangulation,
where a number of

angles
may be required at one point by the instrument.

The method of repetition appears
to be better, it is more time consuming and even many repetitions may yield
ordinary results.

11.
State what errors are eliminated by repetition
method.

1. Errors
due to imperfect eccentricity of verniers and centres are eliminated

by
reading both verniers and taking the mean of the reading.

2. Errors due to imperfect
adjustment of the instrument are eliminated by taking face left and right
observations.

3. Errors due to inaccurate
graduations on the main scale are eliminated as the readings are spread over
different parts of the circle.

4. Errors due to inaccurate
bisection of the signal are eliminated, as they tend to balance each other. All
the errors are also minimized as the number of repetitions divides the sum.

12.
What are the methods used to plot the traverse?

1. By
parallel Meridians Through Each Station.

2. By
Included Angles

3. By Paper
Protractor.

4. By
rectangular co-ordinates.

5.
Plotting by tangents and chords.

13.Define
closing error.

If a closed traverse is plotted
according to the field measurements, the end point of the traverse will not
coincide exactly with the starting point, due to the errors in the field
observations. Such as error is known as closing error.

Closing
error e = ? ( ?L) ^{2}
+ ( ?D) ^{2}.

where, ?L =
sum of latitudes.

?D = sum of departures.

The
direction of closing error

tan
? = ?D / ?L.

14.
Define: Balancing. What are the methods used to balancing the traverse?

The term balancing is generally
applied to the operation of applying corrections to latitudes and departures.
So that ?L = sum
of latitudes = 0; ?D = sum of departures = 0. This
is applied only for closed traverse

Methods
used to balancing (adjusting) the traverse:

1.
Bowditch’s rule

2. Transit
rule.

3. Graphical
method.

4. Axis
method.

15.Explain
the Bowditch’s rule in balancing the traverse.

The Bowditch’s rule
(compass rule) is used to balance a traverse where the linear and angular
measurements are of equal precision. In this method the error in linear
measurements are proportional to ?l and the
error in angular measurements are inversely proportional to ?l
,where
l is the length of the line.

Correction
to latitude (or departure) of any side

= Total error in latitude (or
departure) x [ Length of that side / Perimeter of traverse.]

C
_{L} = ? L .( l / ?l)

C
_{D} = ? D .( l / ?l)

where,

?
L = Total error in Latitude.

?
D = Total error in
Departure.

l = Length of the side ?l =
Perimeter of traverse.

16.
What is Gale’s table? What is its use?

Traverse computations are usually
done in a tabular form. One such form is known as Gale’s Table.

It
is used to balance the traverse and also used to find the area of the closed

traverse.

17.
Define: Omitted measurements.

Sometimes it is not possible to
take all the measurements due to obstacles. Such missing quantities are known
as omitted measurements. They can be calculated from the known latitudes and
departures.

18.
What is closed traverse? What are the two checks applicable in this case?

When the lines form a circuit,
which ends at the starting point, it is known as closed traverse.

__Check:__

(i). Sum of interior angles = (2n – 4) 90
(ii). Sum of exterior angles = (2n +4) 90

Where,
n= number of sides of the traverse.

19.
Define: Trigonometrical leveling or Heights and Distances.

Trigonometrical leveling is an
indirect method of levelling. The relative elevations of various points are
determined from the observed vertical angles and horizontal distances by the
use of trigonometrical relations. The vertical angles are measured with a
theodolite and the horizontal distances are measured with a tape or chain. This
method is also known as Heights and Distances.

20. What are the methods used to find the
elevations of the points in the case of inaccessible points? Differentiate
that?

1. Single
plane method

2.
Double plane method.

Single plane method

Two
instrument stations are chosen in line with the object.

The two
vertical angles are measured in the same vertical plane.

Horizontal
angles are not required.

Double
plane method

Two
instrument stations are chosen which are not in line with the object.

The two
vertical angles are measured in two different vertical planes.

Horizontal
angles are also measured.

Tags : Civil Surveying - Theodolite Surveying

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