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SURVEYING
SURVEYING
Preamble
Preamble
Surveying is involved in a project from conceptual stage
Surveying is involved in a project from conceptual stage
to construction and afterwards in maintenance also.
to construction and afterwards in maintenance also.
Depending on the stage at which surveying is carried
Depending on the stage at which surveying is carried
out it can be called.
out it can be called.
i)
i) Pre construction
Pre construction
survey
survey
Feasibility survey (RECT, PECT)
Feasibility survey (RECT, PECT)
ii)
ii) Construction
Construction
survey
survey
To maintain alignment and
To maintain alignment and
Geometry control during
Geometry control during
construction. (FLS and other )
construction. (FLS and other )
iii)
iii) Post
Post
construction
construction
Maintenance survey
Maintenance survey
3. Definition : Operation of making such
Definition : Operation of making such
measurements that the relative position of
measurements that the relative position of
various features, natural or Artificial on the
various features, natural or Artificial on the
surface of the earth can be exhibited in their
surface of the earth can be exhibited in their
correct Horizontal and vertical relationship.
correct Horizontal and vertical relationship.
Normally determining position in
Normally determining position in
Horizontal plane is called surveying.
Horizontal plane is called surveying.
Determining relative heights or depth is
Determining relative heights or depth is
called levelling.
called levelling.
4. Purpose
Purpose : The main object of surveying is the preparation
: The main object of surveying is the preparation
of maps or plans which are the basis in planning and design
of maps or plans which are the basis in planning and design
of engineering project such as route location of railway line,
of engineering project such as route location of railway line,
roads and water supply scheme.
roads and water supply scheme.
Basic Principles in Surveying
Basic Principles in Surveying : Ruling principle of
: Ruling principle of
survey is :
survey is :
i) “ to work from whole to part”. For surveying Establish
i) “ to work from whole to part”. For surveying Establish
control points with high precision by use of Triangulation
control points with high precision by use of Triangulation
and precise levelling. Area is further divided into triangle,
and precise levelling. Area is further divided into triangle,
which are surveyed with less accuracy.
which are surveyed with less accuracy.
ii) to fix the position of new stations by atleast two
ii) to fix the position of new stations by atleast two
independent processes – By linear and Angular
independent processes – By linear and Angular
5. Classification of Surveys
Classification of Surveys :
: Surveying is divided into two
Surveying is divided into two
main categories-
main categories-
i) Geodetic Survey
i) Geodetic Survey
ii) Plane survey
ii) Plane survey
i) Geodetic Survey :-
i) Geodetic Survey :- When survey extends over a large
When survey extends over a large
areas more than 200 sq. km. and degree of accuracy is also
areas more than 200 sq. km. and degree of accuracy is also
great. The curvature of earth is also taken into account.
great. The curvature of earth is also taken into account.
Geodetic survey is used to provide control points to which
Geodetic survey is used to provide control points to which
small surveys can be connected.
small surveys can be connected.
ii) Plane Survey :-
ii) Plane Survey :- For small projects covering Area less
For small projects covering Area less
than 200 sq.km. Earth curvature is not counted for in
than 200 sq.km. Earth curvature is not counted for in
distances. Earth surface is considered as plane. (Angular
distances. Earth surface is considered as plane. (Angular
error of 1” in 200 sq. km. area by assuming plane).
error of 1” in 200 sq. km. area by assuming plane).
6. A)
A) Classification based upon equipment used
Classification based upon equipment used:
:
i) Chain survey
i) Chain survey
ii) Compass survey
ii) Compass survey
iii) Theodolite survey
iii) Theodolite survey
iv) Plane Table survey
iv) Plane Table survey
v) Tachometric survey
v) Tachometric survey
vi) Aerial Photographic Survey
vi) Aerial Photographic Survey
vi) Remote sensing.
vi) Remote sensing.
B) Based upon Method Employed :
B) Based upon Method Employed :
i) Triangulation :
i) Triangulation : Control points are established
Control points are established
through a net-work of triangles.
through a net-work of triangles.
ii) Traversing:
ii) Traversing: Scheme of control points consisting of
Scheme of control points consisting of
a series of connected lines.
a series of connected lines.
iii) Trilateration:
iii) Trilateration: Distances are measured for
Distances are measured for
exercising the control.
exercising the control.
7. Levelling :
Levelling :
The art of determining relative altitudes
The art of determining relative altitudes
of points on the surface of the earth of
of points on the surface of the earth of
beneath the surface of earth is called
beneath the surface of earth is called
LEVELLING.
LEVELLING.
For execution of Engineering Projects it
For execution of Engineering Projects it
is very necessary to determine
is very necessary to determine
elevations of different points along the
elevations of different points along the
alignment of proposed project.
alignment of proposed project.
8. Other applications are :
Other applications are :
i) Taking rail levels existing before track renewals to
i) Taking rail levels existing before track renewals to
finalise final rail level profile including vertical
finalise final rail level profile including vertical
curves.
curves.
ii) Initial ground levels for earthwork calculations.
ii) Initial ground levels for earthwork calculations.
iii) Levels for measurement of earthwork.
iii) Levels for measurement of earthwork.
iv) Measurement of ballast etc.
iv) Measurement of ballast etc.
Terms used in Levelling –
Terms used in Levelling –
a) DATUM – or Datum plane is an arbitrarily
a) DATUM – or Datum plane is an arbitrarily
assumed level surface or line with reference to which
assumed level surface or line with reference to which
level of other line or surface are calculated.
level of other line or surface are calculated.
9. b) REDUCED LEVEL (RL) –
b) REDUCED LEVEL (RL) – Height or depth of a
Height or depth of a
point above or below the assumed datum is called
point above or below the assumed datum is called
Reduced level.
Reduced level.
c) BENCH MARK –
c) BENCH MARK – (BM) –
(BM) – B.M. is a fixed reference
B.M. is a fixed reference
point of known elevation. It may be of the
point of known elevation. It may be of the
following types.
following types.
i) GTS Bench mark (
i) GTS Bench mark (Geodetic Triangulation Survey) :
Geodetic Triangulation Survey) :
These Bench marks are established by national
These Bench marks are established by national
agency like Survey of India. They are established
agency like Survey of India. They are established
with highest precision. Their position and
with highest precision. Their position and
elevation above MSL is given in a special catalogue
elevation above MSL is given in a special catalogue
known as GTS Maps ( 100 km. interval).
known as GTS Maps ( 100 km. interval).
10. ii)
ii) Permanent Bench Mark :
Permanent Bench Mark : They are
They are
fixed points of reference establish with reference
fixed points of reference establish with reference
to GTS Bench mark (10 km. interval).
to GTS Bench mark (10 km. interval).
iii) Arbitrary Bench mark :
iii) Arbitrary Bench mark : These are
These are
reference points whose elevations are arbitrarily
reference points whose elevations are arbitrarily
assumed. In most of Engineering projects, the
assumed. In most of Engineering projects, the
difference in elevation is more important than
difference in elevation is more important than
their reduced levels with reference to MSL as
their reduced levels with reference to MSL as
given in a special catalogue known as GTS Maps (
given in a special catalogue known as GTS Maps (
100 Km. interval).
100 Km. interval).
11. d)
d)Mean Sea Level (M.S.L.) :
Mean Sea Level (M.S.L.) : M.S.L. is obtained by
M.S.L. is obtained by
making hourly observations of the tides at any place
making hourly observations of the tides at any place
over a period of 19 years. MSL adopted by Survey
over a period of 19 years. MSL adopted by Survey
of India is now Bombay which was Karachi earlier.
of India is now Bombay which was Karachi earlier.
e) Level Surface :
e) Level Surface : The surface which is parallel to
The surface which is parallel to
the mean sphereoidal surface of the earth is known
the mean sphereoidal surface of the earth is known
as level surface.
as level surface.
f
f) Line of Collimation :
) Line of Collimation : It is the line joining the
It is the line joining the
intersection of the cross hair and the optical center
intersection of the cross hair and the optical center
of the objective and its extensions, it is also called
of the objective and its extensions, it is also called
line of sight or collimation.
line of sight or collimation.
12. g)
g) Height of Instrument (HI) :
Height of Instrument (HI) : The elevation of the line of
The elevation of the line of
sight with respect to assumed datum is known as HI.
sight with respect to assumed datum is known as HI.
h) Back sight : (B.S.) -
h) Back sight : (B.S.) - The first sight taken on a levelling
The first sight taken on a levelling
staff held at a point of known elevation. B.S. enables the
staff held at a point of known elevation. B.S. enables the
surveyor to obtain HI +sight i.e. Height of Instrument or
surveyor to obtain HI +sight i.e. Height of Instrument or
line of sight.
line of sight.
i) Fore Sight : (F.S.) –
i) Fore Sight : (F.S.) – It is the last staff reading taken from a
It is the last staff reading taken from a
setting of the level. It is also termed as minus sight.
setting of the level. It is also termed as minus sight.
Fore sight is the sight taken on a levelling staff held at a
Fore sight is the sight taken on a levelling staff held at a
point of unknown elevation to ascertain the amount by
point of unknown elevation to ascertain the amount by
which the point is above or below the line of sight. This is
which the point is above or below the line of sight. This is
also called minus sight as the foresight reading is always
also called minus sight as the foresight reading is always
subtracted from height of Instrument.
subtracted from height of Instrument.
13. k) Change Point (CP) :
k) Change Point (CP) : The point on which
The point on which
both the foresight and back sight are taken
both the foresight and back sight are taken
during the operation of levelling is called
during the operation of levelling is called
change point.
change point.
l) Intermediate Sight (IS) :
l) Intermediate Sight (IS) :
The foresight taken on a levelling staff held
The foresight taken on a levelling staff held
at a point between two turning points, to
at a point between two turning points, to
determine the elevation of that point, is
determine the elevation of that point, is
known as intermediate sight.
known as intermediate sight.
14. It may be noted that for one setting of a level, there
It may be noted that for one setting of a level, there
will be only one back sight and one foresight but
will be only one back sight and one foresight but
there can be any number of intermediate sights.
there can be any number of intermediate sights.
Type of Levelling Equipments:
Type of Levelling Equipments:
i)
i) Dumpy level
Dumpy level
ii) Tilting level
ii) Tilting level
iii) Automatic level
iii) Automatic level
iv) Digital Auto level
iv) Digital Auto level
Dumpy level :
Dumpy level : It is simple compact and stable.
It is simple compact and stable.
The telescope is rigidly fixed to its support
The telescope is rigidly fixed to its support
therefore cannot be rotated about its longitudinal
therefore cannot be rotated about its longitudinal
axis. A long bubble tube is attached to the top of
axis. A long bubble tube is attached to the top of
telescope. Dumpy literally means short and thick.
telescope. Dumpy literally means short and thick.
15. Tilting level :
Tilting level : It consists of a telescope
It consists of a telescope
attached with a level tube which can be tilted
attached with a level tube which can be tilted
within few degrees in vertical plane by a tilting
within few degrees in vertical plane by a tilting
screw.
screw.
The main peculiarity of this level is that the
The main peculiarity of this level is that the
vertical axis need not be truly vertical, since the
vertical axis need not be truly vertical, since the
line of collimation is not perpendicular to it.
line of collimation is not perpendicular to it.
The line of collimation, is, however, made
The line of collimation, is, however, made
horizontal for each pointing of telescope by
horizontal for each pointing of telescope by
means of tilting screw. It is mainly designed
means of tilting screw. It is mainly designed
for precise levelling work.
for precise levelling work.
16. The Automatic level :
The Automatic level : Also termed as
Also termed as
self aligning level. The fundamental
self aligning level. The fundamental
difference between automatic and the
difference between automatic and the
classic spirit level is that in the former
classic spirit level is that in the former
the line of sight is no longer levelled
the line of sight is no longer levelled
manually using a tubular spirit level,
manually using a tubular spirit level,
but is levelled automatically within a
but is levelled automatically within a
certain tilt range. This is achieved by
certain tilt range. This is achieved by
compensator in the telescope.
compensator in the telescope.
17. Advantage of automatic level
Advantage of automatic level
i) Much simpler to use
i) Much simpler to use
ii) High precision – Mean elevation error
ii) High precision – Mean elevation error
on staff graduated to 5mm division varies
on staff graduated to 5mm division varies
between +0.5 to 0.8 mm per km of
between +0.5 to 0.8 mm per km of
forward and backward levelling.
forward and backward levelling.
iii) High speed : For fly levelling the
iii) High speed : For fly levelling the
progress achieved by various level-wise
progress achieved by various level-wise
compared.
compared.
18. Type of level D(m) 20m 40 60 80 100 120
Type of level D(m) 20m 40 60 80 100 120
Automatic level speed 1.2 2 2.4 2.5 2.6 2.7
Automatic level speed 1.2 2 2.4 2.5 2.6 2.7
S(Km/hr)
S(Km/hr)
Tilting level speed 0.6 1.1 1.5 1.7 1.8 1.9
Tilting level speed 0.6 1.1 1.5 1.7 1.8 1.9
S(Km/hr)
S(Km/hr)
S = Speed of levelling in km/hr.
S = Speed of levelling in km/hr.
D = Sighting distance in meter.
D = Sighting distance in meter.
The speed of Dumpy level is about 25% lower than
The speed of Dumpy level is about 25% lower than
tilting level.
tilting level.
iv)
iv) Freedom from errors
Freedom from errors – Accuracy is increased
– Accuracy is increased
by an errect telescope image.
by an errect telescope image.
v) Range of application
v) Range of application – level can be used on
– level can be used on
medium and large sized projects and setting bench
medium and large sized projects and setting bench
marks.
marks.
19. Basic components of level :
Basic components of level :
1. Telescope
1. Telescope – to provide a line of sight
– to provide a line of sight
2. Level Tube
2. Level Tube – to make line of sight horizontal
– to make line of sight horizontal
3. Levelling head
3. Levelling head – to bring the bubble of tube
– to bring the bubble of tube
level at the centre of its run.
level at the centre of its run.
4. Tripod
4. Tripod – to support the above three parts of the
– to support the above three parts of the
level.
level.
1. TELESCOPE
1. TELESCOPE : Telescope is an optical
: Telescope is an optical
instrument used for magnifying and viewing the
instrument used for magnifying and viewing the
images of distant objects. It consists of two lenses.
images of distant objects. It consists of two lenses.
The lens fitted near the eye is called the eye piece
The lens fitted near the eye is called the eye piece
and the other fitted at the end near to the object is
and the other fitted at the end near to the object is
called the objective lens.
called the objective lens.
20. The objective provides a real inverted image
The objective provides a real inverted image
infront of the eye piece at a distance lesser than
infront of the eye piece at a distance lesser than
its focal distance.
its focal distance.
Two essential conditions are involved. :
Two essential conditions are involved. :
i) The real image of the object, must be
i) The real image of the object, must be
formed.
formed.
Ii) the plane of image must coincide with that
Ii) the plane of image must coincide with that
of cross hairs.
of cross hairs.
Focusing of Telescope : The operation of
Focusing of Telescope : The operation of
obtaining a clear image of the object in the
obtaining a clear image of the object in the
plane of cross hairs is known as focusing.
plane of cross hairs is known as focusing.
21. 1. Diaphram :
1. Diaphram : A frame carrying cross hairs usually
A frame carrying cross hairs usually
made of either silk thread or platinum wire and placed
made of either silk thread or platinum wire and placed
at the plane at which vertical image of the object is
at the plane at which vertical image of the object is
formed by the objective.
formed by the objective.
Vertical hair of the diaphram enables the surveyor to
Vertical hair of the diaphram enables the surveyor to
check the verticality of levelling staff whereas
check the verticality of levelling staff whereas
horizontal hairs are used to read the staff graduations.
horizontal hairs are used to read the staff graduations.
2.Level Tube :
2.Level Tube : Also known as Bubble Tube consists
Also known as Bubble Tube consists
of a glass tube placed in a brass tube which is sealed
of a glass tube placed in a brass tube which is sealed
with plaster of paris. The whole of the interior surface
with plaster of paris. The whole of the interior surface
or the upper half is accurately ground so that its
or the upper half is accurately ground so that its
longitudinal section, is an arc of a circle. Level tube is
longitudinal section, is an arc of a circle. Level tube is
filled with either or alcohol, the remaining space is
filled with either or alcohol, the remaining space is
occupied by an air bubble. The centre of air bubble
occupied by an air bubble. The centre of air bubble
always rest at the highest point of the tube.
always rest at the highest point of the tube.
22. Outer surface of the bubble tube is graduated in
Outer surface of the bubble tube is graduated in
both the directions from the centre.
both the directions from the centre.
The line tangential to the circular are at its
The line tangential to the circular are at its
highest point i.e. the middle of tube is called the
highest point i.e. the middle of tube is called the
axis of bubble tube. When the bubble is central
axis of bubble tube. When the bubble is central
the axis of bubble becomes Horizontal.
the axis of bubble becomes Horizontal.
The level tube is attached on the top of Telescope
The level tube is attached on the top of Telescope
by means of capstan headed nuts.
by means of capstan headed nuts.
23. 3.
3.Levelling head :
Levelling head : Levelling head generally
Levelling head generally
consists of two parallel plates with 3 foot
consists of two parallel plates with 3 foot
screws. Upper plate is known as Tribrach
screws. Upper plate is known as Tribrach
and lower plate is trivet which can be
and lower plate is trivet which can be
screwed on to the tripod. Levelling head has
screwed on to the tripod. Levelling head has
to perform 3 distant functions :
to perform 3 distant functions :
i) to support the telescope
i) to support the telescope
ii) to attach the level to the tripod
ii) to attach the level to the tripod
iii) to provide a means for level (foot screws)
iii) to provide a means for level (foot screws)
24. Adjustment of level :
Adjustment of level :
i) Temporarily Adjustments – adjustments which
i) Temporarily Adjustments – adjustments which
are made for every setting of a level.
are made for every setting of a level.
ii) Permanent adjustments- required if some error is
ii) Permanent adjustments- required if some error is
there in instrument.
there in instrument.
i) Temporary Adjustments : includes
i) Temporary Adjustments : includes
a) setting up the level
a) setting up the level
b) levelling up
b) levelling up
c) elimination of parallax
c) elimination of parallax
a) Setting up the level :
a) Setting up the level : This operation includes
This operation includes
fixing the instrument on the tripod and also
fixing the instrument on the tripod and also
approximate levelling by leg adjustment.
approximate levelling by leg adjustment.
25. b) Levelling up :
b) Levelling up : Accurate levelling is done with
Accurate levelling is done with
the help of foot screws and by using plate levels. The
the help of foot screws and by using plate levels. The
object of levelling up the instrument is to make its
object of levelling up the instrument is to make its
vertical axis truly vertical.
vertical axis truly vertical.
c) Elimination of parallax :
c) Elimination of parallax : If the image formed
If the image formed
by the objective does not lie in the plane of the cross
by the objective does not lie in the plane of the cross
hairs, there will be a shift in the image due to shift of
hairs, there will be a shift in the image due to shift of
the eye. Such displacement of image is termed as
the eye. Such displacement of image is termed as
parallax. Parallax is removed in two stages.
parallax. Parallax is removed in two stages.
1) Focusing the eye for distinct vision of cross hairs.
1) Focusing the eye for distinct vision of cross hairs.
2) Focusing the objective so that image is formed in
2) Focusing the objective so that image is formed in
the plane of cross hairs.
the plane of cross hairs.
26. Principles of levelling :
Principles of levelling :
a) Simple levelling : The operation of
a) Simple levelling : The operation of
levelling for determining the difference
levelling for determining the difference
in elevation, if not too great between two
in elevation, if not too great between two
points visible from single position of the
points visible from single position of the
level is known as simple levelling.
level is known as simple levelling.
PROCEDURE : Following steps are
PROCEDURE : Following steps are
involved.
involved.
27. 1.
1.Level the instrument correctly.
Level the instrument correctly.
2. Direct the telescope towards the staff held
2. Direct the telescope towards the staff held
3. Take the reading of Central, horizontal hair of the
3. Take the reading of Central, horizontal hair of the
diaphram, where it appears to cut the staff ensuring
diaphram, where it appears to cut the staff ensuring
that the bubble is central.
that the bubble is central.
4. Send the staff to next point
4. Send the staff to next point
5. Direct the telescope towards C and focus it again
5. Direct the telescope towards C and focus it again
6. Check up the bubble if central, if not bring it to
6. Check up the bubble if central, if not bring it to
the Central position by the foot screw nearest to the
the Central position by the foot screw nearest to the
telescope.
telescope.
7. Take the reading of Central Horizontal cross hair.
7. Take the reading of Central Horizontal cross hair.
28. b) Differential levelling or fly levelling :
b) Differential levelling or fly levelling :
This method is used in order to find the
This method is used in order to find the
difference in elevation between two points.
difference in elevation between two points.
i) If they are too far apart
i) If they are too far apart
ii) if the difference in elevation between them
ii) if the difference in elevation between them
is too great.
is too great.
iii) If there are obstacles intervening. In such
iii) If there are obstacles intervening. In such
case it is necessary to set up the level in
case it is necessary to set up the level in
several positions and to work in series of
several positions and to work in series of
stages.
stages.
29. The difference of level of the points A&B is
The difference of level of the points A&B is
equal to the algebraic sum of these difference
equal to the algebraic sum of these difference
between the sum of back sights and sum of the
between the sum of back sights and sum of the
fore sights i.e.
fore sights i.e. Σ
Σ BS -
BS - Σ
Σ FS
FS
Booking and reduction of the levels may be
Booking and reduction of the levels may be
done by following 2 methods.
done by following 2 methods.
i) Rise and fall method
i) Rise and fall method
ii) Height of collimation method
ii) Height of collimation method
30. RISE AND FALL METHOD –
RISE AND FALL METHOD –
In this method, the difference of level between two
In this method, the difference of level between two
consecutive points for each setting of the instrument is
consecutive points for each setting of the instrument is
obtained by comparing their staff readings.
obtained by comparing their staff readings.
The difference between their staff readings indicates a
The difference between their staff readings indicates a
rise if back sight is more than foresight and a fall if it is less
rise if back sight is more than foresight and a fall if it is less
than foresight.
than foresight.
The Rise and Fall worked out for all the points given
The Rise and Fall worked out for all the points given
the vertical distances of each point relative to the proceeding
the vertical distances of each point relative to the proceeding
one.
one.
If the RL of the Back staff point is known, then RL of
If the RL of the Back staff point is known, then RL of
the following staff point may be obtained by adding its rise
the following staff point may be obtained by adding its rise
or substracting fall from the RL of preceding point.
or substracting fall from the RL of preceding point.
31. Height of Collimation Method:
Height of Collimation Method:
In this method Height of Instrument
In this method Height of Instrument
(H.I.) is calculated for each setting of the
(H.I.) is calculated for each setting of the
instrument by adding the back sight (B.S.)
instrument by adding the back sight (B.S.)
to the elevation of B.M.
to the elevation of B.M.
Height of instrument (H.I.) = R.L. of the
Height of instrument (H.I.) = R.L. of the
plane of collimation
plane of collimation
= R.L. of B.M.+B.S.
= R.L. of B.M.+B.S.
32. RL of a point = H.I. – FS
RL of a point = H.I. – FS
Or = H.I. – IS
Or = H.I. – IS
- After every back sight, there may be many
- After every back sight, there may be many
intermediate sights but there must be only
intermediate sights but there must be only
one foresight.
one foresight.
- The B.S. & F.S. forms the two ends of one
- The B.S. & F.S. forms the two ends of one
stage in levelling.
stage in levelling.
- Levelling should always commence from a
- Levelling should always commence from a
permanent B.M. and end on a permanent
permanent B.M. and end on a permanent
B.M.
B.M.
34. THEODOLITE -
THEODOLITE - An instrument used for measuring
An instrument used for measuring
horizontal and vertical angles accurately is known
horizontal and vertical angles accurately is known
as theodolite.
as theodolite.
Uses of Theodolite
Uses of Theodolite
i) Measurement of Horizontal and vertical angles.
i) Measurement of Horizontal and vertical angles.
Ii) Setting out lines and angles
Ii) Setting out lines and angles
iii) Optical distance measurement
iii) Optical distance measurement
iv) Plumbing tall building
iv) Plumbing tall building
v) Setting out of Railway curves
v) Setting out of Railway curves
vi) Locating the position of piers for Bridge etc.
vi) Locating the position of piers for Bridge etc.
vii) Geographical position fixing from observation
vii) Geographical position fixing from observation
of sun and stars.
of sun and stars.
viii) Alignment control in tunnel construction.
viii) Alignment control in tunnel construction.
35. Types of Theodolite : Transit theodolites
Types of Theodolite : Transit theodolites
are categorised into 3 types :
are categorised into 3 types :
1. Vernier theodolite
1. Vernier theodolite
2. Optical Reading Theodolite
2. Optical Reading Theodolite
3. Digital Theodolite/Electronic Theodolite
3. Digital Theodolite/Electronic Theodolite
Basically Transit Theodolite are those in
Basically Transit Theodolite are those in
which the telescope can revolve through a
which the telescope can revolve through a
complete revolution about its Horizontal
complete revolution about its Horizontal
axis in vertical plane.
axis in vertical plane.
36. Components of Transit theodolite –
Components of Transit theodolite –
Transit theodolite consists of the
Transit theodolite consists of the
following parts :
following parts :
1.
1. Levelling Head
Levelling Head
2.
2. Lower Plate or Scale Plate
Lower Plate or Scale Plate
3.
3. Upper Plate or Vernier Plate
Upper Plate or Vernier Plate
4.
4. The standard or A Frame
The standard or A Frame
5.
5. T-Frame or Index Bar.
T-Frame or Index Bar.
6.
6. Plate Levels
Plate Levels
7.
7. Telescope
Telescope
37. 1.
1.Levelling Head -
Levelling Head - Levelling Head
Levelling Head
consists of upper tribrach and lower
consists of upper tribrach and lower
Tribrach. Upper tribrach has three arms,
Tribrach. Upper tribrach has three arms,
each arm carries a levelling screw for
each arm carries a levelling screw for
levelling the equipment. Lower tribrach has
levelling the equipment. Lower tribrach has
got a circular hole through which a plumb
got a circular hole through which a plumb
bob may be suspended for centering.
bob may be suspended for centering.
Three distinct functions of levelling head
Three distinct functions of levelling head
are:
are:
i) to support the main part of the instrument
i) to support the main part of the instrument
ii) to attach the Theodolite to the Tripod
ii) to attach the Theodolite to the Tripod
iii) to provide a means for levelling the
iii) to provide a means for levelling the
theodolite
theodolite
38. 2.
2. Lower Plate
Lower Plate (Scale Plate) :
(Scale Plate) : Lower Plate which
Lower Plate which
is attached to outer spindle, carries a horizonta
is attached to outer spindle, carries a horizonta
graduated circle, it is graduated from 0-360. Each
graduated circle, it is graduated from 0-360. Each
degree is further divided into 10 minutes or 20
degree is further divided into 10 minutes or 20
minutes. Scale plate can be clamped to any
minutes. Scale plate can be clamped to any
position by a clamping screw and a
position by a clamping screw and a
corresponding slow motion screw.
corresponding slow motion screw.
When the lower plate is tightened, the lower
When the lower plate is tightened, the lower
plate is fixed to the upper tribrach of the levelling
plate is fixed to the upper tribrach of the levelling
head. The size of the Theodolite is determined
head. The size of the Theodolite is determined
by the size of the diameter of this lower plate.
by the size of the diameter of this lower plate.
39. 3.
3.Upper plate or Vernier Plate :
Upper plate or Vernier Plate : Upper plate is
Upper plate is
attached to Inner spindle axis. Two verniers are screwed
attached to Inner spindle axis. Two verniers are screwed
to the upper plats. It carries an upper clamp screw and
to the upper plats. It carries an upper clamp screw and
tangent screw. On clamping the upper clamp and
tangent screw. On clamping the upper clamp and
unclamping the lower clamp, the instrument may be
unclamping the lower clamp, the instrument may be
rotated on its outer spindle without any relative motion
rotated on its outer spindle without any relative motion
between the two plates.
between the two plates.
On the other hand if lower clamp screw is
On the other hand if lower clamp screw is
tightened and upper clamp screw is unclamped, the
tightened and upper clamp screw is unclamped, the
instrument may be rotated about its inner spindle with a
instrument may be rotated about its inner spindle with a
relative motion between the vernier and graduated scale
relative motion between the vernier and graduated scale
of the lower plate. This property is utilised for measuring
of the lower plate. This property is utilised for measuring
angles.
angles.
40. 4
4. Plate Levels -
. Plate Levels - Upper plates carries two plate
Upper plates carries two plate levels
levels
placed at right angles to each other. One of the plate bubble
placed at right angles to each other. One of the plate bubble
is kept parallel to the trunion axis. Plate levels can be
is kept parallel to the trunion axis. Plate levels can be
centred with the help of foot screws.
centred with the help of foot screws.
5. Telescope –
5. Telescope – Telescope is supported on the pivots of
Telescope is supported on the pivots of
the trunion axis which affords its movement in the vertical
the trunion axis which affords its movement in the vertical
plane.
plane.
IMPORTANT DEFINITIONS –
IMPORTANT DEFINITIONS –
I) Line of Collimation
I) Line of Collimation - the line which passes
- the line which passes
through the Intersection of the cross hairs of the eye piece
through the Intersection of the cross hairs of the eye piece
and optical centre of the objective and its continuation is
and optical centre of the objective and its continuation is
called as line of collimation. This is also known as line of
called as line of collimation. This is also known as line of
sight.
sight.
41. ii)
ii)Transiting -
Transiting - The process of turning the
The process of turning the
telescope in vertical plane through 180 deg.
telescope in vertical plane through 180 deg.
about its horizontal axis is known as
about its horizontal axis is known as
transiting.
transiting.
iii) Swing -
iii) Swing - A continuous motion of
A continuous motion of
telescope about the vertical axis in horizontal
telescope about the vertical axis in horizontal
plane is called swing. The swing may be in
plane is called swing. The swing may be in
either direction i.e. Right swing or left swing.
either direction i.e. Right swing or left swing.
42. iv) Face left observation –
iv) Face left observation – When vertical circle is on
When vertical circle is on
the left of the telescope at the time of observation, the
the left of the telescope at the time of observation, the
observations are called face left observation.
observations are called face left observation.
v) Face right observation –
v) Face right observation – When vertical circle is
When vertical circle is
on the right of the telescope at the time of observation.
on the right of the telescope at the time of observation.
TEMPORARY ADJUSTMENT OF
TEMPORARY ADJUSTMENT OF
THEODOLITE
THEODOLITE
1) Setting up the Theodolite over the station
1) Setting up the Theodolite over the station
2) Levelling up the theodolite
2) Levelling up the theodolite
3) Elimination of the parallax
3) Elimination of the parallax
43. 1.
1.Setting up :
Setting up : Operation of setting up a theodolite
Operation of setting up a theodolite
includes:
includes:
a) centering the theodolite over the ground mark
a) centering the theodolite over the ground mark
b) approximate levelling with the help of tripod legs.
b) approximate levelling with the help of tripod legs.
2. Levelling up of theodolite
2. Levelling up of theodolite
The operation of making the vertical axis
The operation of making the vertical axis
truly vertical is known as levelling of
truly vertical is known as levelling of
Theodolite.
Theodolite.
i) Turn the horizontal plate until the
i) Turn the horizontal plate until the
longitudinal axis of the plate level is
longitudinal axis of the plate level is
approximately parallel to a line joining any
approximately parallel to a line joining any
two levelling screws.
two levelling screws.
44. ii)
ii) Bring the bubble to the centre of its run by turning both
Bring the bubble to the centre of its run by turning both
foot screws simultaneously in opposite directions either
foot screws simultaneously in opposite directions either
inwards or outwards. The movement of the left thumb
inwards or outwards. The movement of the left thumb
indicates the direction of movement of bubble.
indicates the direction of movement of bubble.
iii) Turn the instrument through 180
iii) Turn the instrument through 1800
0
in azimuth.
in azimuth.
iv) Note the position of the bubble. If it occupies a different
iv) Note the position of the bubble. If it occupies a different
position, move it by means of the same two foot screws to the
position, move it by means of the same two foot screws to the
approx. mean of the two positions.v) Turn the theodolite
approx. mean of the two positions.v) Turn the theodolite
through 90 in azimuth so that the plate level becomes
through 90 in azimuth so that the plate level becomes
perpendicular to the previous position.
perpendicular to the previous position.
vi) With the help of third floor screw, move the bubble to the
vi) With the help of third floor screw, move the bubble to the
approx. mean position already indicated.
approx. mean position already indicated.
45. vii) Repeat the process until the bubble, retains
vii) Repeat the process until the bubble, retains
the same position for every setting of the
the same position for every setting of the
instrument.
instrument.
3. Elimination of Parallax :
3. Elimination of Parallax : Elimination of parallax
Elimination of parallax
may be done by focusing the eye piece for distinct
may be done by focusing the eye piece for distinct
vision of cross hairs and focusing the objective to bring
vision of cross hairs and focusing the objective to bring
the image of the object in the plane of cross hairs.
the image of the object in the plane of cross hairs.
Measurement of Horizontal Angle
Measurement of Horizontal Angle
Procedure : to measure a Horizontal Angle
Procedure : to measure a Horizontal Angle
ABC between BA & BC the following
ABC between BA & BC the following
procedure is followed.
procedure is followed.
46. 1.
1.Set up, Centre and level the theodolite over
Set up, Centre and level the theodolite over
the ground point B.
the ground point B.
2. Loosen the upper plate, set the vernier to
2. Loosen the upper plate, set the vernier to
read zero and clamp the upper clamp.
read zero and clamp the upper clamp.
3. Loosen the lower plate and swing the
3. Loosen the lower plate and swing the
telescope until the left point A is sighted.
telescope until the left point A is sighted.
Tighten the lower clamp. Accurate bisection
Tighten the lower clamp. Accurate bisection
of the arrow held on the Point A is done by
of the arrow held on the Point A is done by
using the lower tangent screw. Read both
using the lower tangent screw. Read both
the vernier and take the mean of the reading.
the vernier and take the mean of the reading.
47. 4. Unclamp the upper plate and swing the
4. Unclamp the upper plate and swing the
telescope in clockwise direction until point C
telescope in clockwise direction until point C
is brought in the field of view. Tighten the
is brought in the field of view. Tighten the
upper clamp and bisect the mark of C
upper clamp and bisect the mark of C
accurately, using the upper clamp tangent
accurately, using the upper clamp tangent
screw.
screw.
5. Read both the verniers and take the mean
5. Read both the verniers and take the mean
of readings. The difference of the means of
of readings. The difference of the means of
the reading to C to A is the required angle
the reading to C to A is the required angle
ABC.
ABC.
48. 6. Change the face of the instrument
6. Change the face of the instrument
and repeat the show procedure, the
and repeat the show procedure, the
measure of the angle is again obtained
measure of the angle is again obtained
by taking the difference of the means
by taking the difference of the means
of the readings to C&A on face right.
of the readings to C&A on face right.
7. The mean of the two measures of
7. The mean of the two measures of
the angle ABC on two faces is the
the angle ABC on two faces is the
required value of the angle ABC.
required value of the angle ABC.
