2. LESSON 1
Levelling- Definition
Leveling: is the art of determining the relative heights of different points on, above or below the
earth’s surface. The elevation of a point is the vertical distance above or below a reference surface
called datum.
The datum commonly used is Mean sea level.
Leveling deals with measurements in a vertical plane.
3. LESSON 1
Leveling- Definition
Level Surface: This is a surface which is normal to the direction of gravity at all points as
indicated by a plumb line.
The surface of a still lake may be taken as an example of a level surface.
As the earth is an oblique spheroid, a level surface will not be plane but will be a curved one.
Every point on a level surface is equidistant from the center of the earth.
4. LESSON 1
Leveling- Definition
Elevation of a Point or Reduced Level (RL):
Elevation of a point is the vertical distance above or below the datum. This is usually
called the reduced level (R.L) of the point.
This may be positive or negative accordingly as the point is above or below the datum.
Line of Collimation.
The line of collimation or the line of sight is the line joining the intersection of cross-hairs to the
optical center of the object glass and its continuation.
5. LESSON 1
Leveling- Definition
Axis of Bubble Tube.
The axis of bubble tube or level tube is the line tangential to the longitudinal curve of
bubble tube at its middle point.
This is horizontal when the bubble is centered. This is also called “bubble line.”
Vertical Axis.
The vertical axis is the line about which the telescope can be rotated in a horizontal
plane.
6. REFERENCE:
10-01-2017
SSA
LESSON 1
Leveling- Benchmark
Benchmark (BM):
It is a fixed reference point of known elevation above or below the datum.
Any permanent point whose elevation is known can be used a bench
mark.
They serve as reference points to find the RL of new points.
Different types of Benchmarks:
GTS Bench mark: The great trigonometrical survey bench marks are
established with great precision at intervals throughout the country by
Survey of India. The standard datum adopted is Karachi or Mumbai port.
Permanent Benchmarks: are established at closer intervals between GTS.
They are established on natural or artificial permanent points like isolated
rocks, culverts, parapets, gate pillars or kilometer stones.
Temporary Benchmarks: When they are established temporarily at the end
of day’s work, they are said to temporary benchmarks.
Arbitrary Benchmarks: These bench marks whose elevations are
assumed arbitrarily for leveling of small areas. The assumed elevations do
not refer to any fixed datum such as MSL or GTS.
7. LESSON 1
Leveling- Objectives & uses
Objects/Aim of Leveling:
• To determine the relative heights of different objects on or below the surface of the earth.
• To fix bench marks
• To find profile of a road or railway or canal, etc.
• To show the contours of an area, etc.
Uses of leveling:
• For preparation of a contour map to fix sites for reservoirs, dams, barrages, etc.
• For fixing the alignment of roads, railways, irrigation canals, etc.
• For determining reduced levels of different points on or below the earth’s surface.
• For plotting a longitudinal section and cross sections of a project in order to determine the
volume of earth work.
• To prepare a layout map for water supply, sanitary or drainage schemes.
• To estimate reservoir capacities.
• To set out grades for sewers, etc.
8. LESSON 1
Leveling- Fundamental principle
The fundamental principle of leveling lies in finding out the separation of level lines passing through
a point of known elevation (BM)and that through an unknown point.
Procedure:
Let A represent a point of known elevation Ha and B be a point whose elevation is required to be
determined.
To find out the unknown elevation of B, a level is set up at C in between A& B.
A leveling staff is first held at A and a reading h1 is observed by sighting the staff.
The staff reading at B, say h2 is then taken.
The elevation of the point B i.e Hb is thus given a Ha + (h1-h2)
9. LESSON 1
Leveling- Instruments used
Level- used to fix horizontal line of sight
Leveling staff- used to determine the vertical
distance of points below the horizontal line of
sight.
10. LESSON 1
Leveling- Instruments- Dumpy level
• Simple compact and stable leveling
instrument
• It consists of a telescope, a vertical spindle,
a level tube & a leveling head.
• The telescope tube and the vertical spindle
are rigidly fixed and are cast as one piece
• The leveling head consists of two parallel
plates kept at a distance apart by 3 or 4
leveling screws.
• The telescope can be rotated in HP about
its vertical axis.
• An inclined mirror is attached to the level
tube to enable the observer to view the
bubble from the eyepiece end.
• The bubble is brought to the center by using
foot screws.
11. LESSON 1
Leveling- Instruments- Dumpy level
Advantages of Dumpy level
• It is simple in construction with very few
movable parts
• It requires fewer permanent adjustments
• Adjustments once carries out remain for a
longer period
12. REFERENCE:
10-01-2017
SSA
LESSON 1
Leveling- Instruments- Tilting level
• Preferred for precise & quick leveling
• Telescope and leveling tube can be leveled
by a tilting screw independent of the vertical
axis
• Here the line of collimation is not at right
angles to the vertical axis.
• It is similar to dumpy level in many aspects
but the tilting screw is not rigidly fixed to the
spindle.
• The special feature here is the tilting screw
which helps leveling the instrument quickly.
It acts against a spring
• The tilting screw is graduated to set gradient
lines also.
13. REFERENCE:
10-01-2017
SSA
LESSON 1
Levelling- Instruments- Tilting level
Advantages of Tilting level
• Used for precise leveling work
• The tilting adjustment saves the time
required for temporary adjustments, hence
quick and economical.
• Gradient lines can also be set out.
Disadvantages of tilting level
• Not suitable for taking multiple readings
from one instrument set up as the observer
has to bring the bubble to the center of the
level tube for every reading.
https://www.youtube.com/watch?v=j8poe2vvD2Q
15. LESSON 1
Leveling- Types
Simple Leveling:
• Used when two points are visible from a single position of the level
• Suitable only when the distance between points is within the sighting range of a level.
• The level is set midway between the points.
Example: Let A & B be two points whose difference of elevation is required. RL of point A is 100.00.
P is a point midway AB where level is set up.
16. LESSON 1
Leveling- Types
1. Set up level at P & do all temporary adjustments.
2. Direct the telescope towards A and take a BS, ensuring the bubble is at center. Let the reading
be 1.450 m. Thus, HI= RL of A+BS= 100.000+1.450= 101.450 m
3. Now similarly take the FS at B. Let it be 3.210 m.
Thus RL of B = HI- FS= 101.450-3.210= 98.240.
4. Now difference in elevation between A& B is RL of A – RL of B= 100.000-98.240=1.760
17. LESSON 1
Leveling- Types
Differential Leveling:
• Used when points are farther apart
• Requires more than one setting of instrument to determine the difference.
• Also used when the diff. of elevations is larger or there are intervening obstacles.
• Example:
Let B be the station whose elevation is to be established wrt A. Since the distance is more
differential leveling is carried out from A and terminating at B.
18. LESSON 1
Leveling- Types
• Set up instrument at L1 such that BS at A is clearly visible.
• Then the staff man should move towards B and choose a point S1 such that AL1=L1S1 and FS
is taken.
• Similarly readings are taken from L2, S2and so on moving towards B..
• All staff readings are entered into the level book and RL is calculated by either HI method or
Rise & Fall method
