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Lec 5 and 6 Leveling

Levelling is the process of determining the relative height of points concerning a datum, utilizing horizontal lines of sight to measure vertical distances. The primary methods of levelling include direct and indirect techniques, with various types of levels such as dumpy, tilting, and laser levels. Key concepts include backsight, foresight, height of instrument, and methods for reducing levels like height of instrument and rise and fall methods.

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67 views40 pages

Lec 5 and 6 Leveling

Levelling is the process of determining the relative height of points concerning a datum, utilizing horizontal lines of sight to measure vertical distances. The primary methods of levelling include direct and indirect techniques, with various types of levels such as dumpy, tilting, and laser levels. Key concepts include backsight, foresight, height of instrument, and methods for reducing levels like height of instrument and rise and fall methods.

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xtz364
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© © All Rights Reserved
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Lecture 5

Levelling
Asst. Lect. Mohammed Hashim
Definition
Levelling is defined as “a process of determining the
relative height of different points on, above or below the
ground surface relative to a datum”.
Principle of Levelling
The principle of levelling is to obtain horizontal line of
sight with respect to which vertical distances of the points
above or below this line of sight are found.

Object of levelling
The objective of Levelling
• To Find the elevation of given point with respect to some
assumed reference line called datum.
• To establish point at required elevation respect to datum.
leveling methods

A- Direct leveling:

Differential leveling

B- Indirect leveling:

• Trigonometric leveling
• Barometric leveling
• Hydrostatic leveling
• GPS
A- Direct leveling method

Level

Levelling Staff + Staff bubbles

Tripod
Kinds of Levels

Dumpy Level

Tilting Level

Precise or Geodetic level

Automatic or Self-leveling Level

Laser Level

Electronic Digital (Bar-code) Level

Theodolite and Total Station


Dumpy Level

Precise or
Geodetic
level

Tilting Level
Precise Level
Staff
Automatic Level

Laser Level

Electronic Digital (Bar-code) Level


Theodolite and Total Station
Level components
Field Work
Focusing the staff
How to read level staff

Distance between level and staff = (3.040-2.946)*100 = 9.4 m


Datum
Local Datum
Height of Instrument H.I.
Elevation
Bench Mark BM
Back Sight BS
Foresight FS
Intermediate sight IS
Change Point CP or TP
Basic definitions
Control Surveying
Methods of Reducing Levels

1- Height of instrument method


2- Rise and fall method
DIFFERENTIAL LEVELING

A. Definitions

Dr. Asma
BS = 6.32 ft HI = 106.32 ft FS = 3.10 ft
Point B

Point A Elevation = 103.22 ft

Starting point
(elevation 100.00 ft)
DIFFERENTIAL LEVELING
Definitions
1 . Bench mark (BM) - relatively permanent
point of known elevation
BS = 6.32 ft HI = 106.32 ft FS = 3.10 ft
Point B

Point A Elevation = 103.22 ft

Starting point
(elevation 100.00 ft)
DIFFERENTIAL LEVELING
Definitions
2. Backsight (BS) - a sight taken to the level
rod held at a point of known elevation
(either a BM or TP)
BS = 6.32 ft HI = 106.32 ft FS = 3.10 ft
Point B

Point A Elevation = 103.22 ft

Starting point
(elevation 100.00 ft)
DIFFERENTIAL LEVELING
Definitions
3. Height of instrument (HI) - the elevation
of the line of sight of the telescope
BS = 6.32 ft HI = 106.32 ft FS = 3.10 ft
Point B

Point A Elevation = 103.22 ft

Starting point
(elevation 100.00 ft)
DIFFERENTIAL LEVELING
Definitions
4. Foresight (FS) - a sight taken on any point
to determine its elevation
BS = 6.32 ft HI = 106.32 ft FS = 3.10 ft
Point B

Point A Elevation = 103.22 ft

Starting point
(elevation 100.00 ft)
DIFFERENTIAL LEVELING
B. Computation of Elevations
BS
12.64

BM1
1. BS + Elevation = HI
Elevation 100.00

Point BS HI FS Elevation
BM1 12.64 112.64 100.00
DIFFERENTIAL LEVELING
Computation of Elevations
BS FS
12.64 3.11

BM1
TP1 2. HI - FS = Elevation
Elevation 100.00

Point BS HI FS Elevation
BM1 12.64 112.64 100.00
TP1 3.11 109.53
DIFFERENTIAL LEVELING
Computation of Elevations
BS
BS FS 10.88
12.64 3.11

BM1
TP1
Elevation 100.00

Point BS HI FS Elevation
BM1 12.64 112.64 100.00
TP1 10.88 120.41 3.11 109.53
DIFFERENTIAL LEVELING
Computation of Elevations
BS FS
BS FS 10.88 2.56
12.64 3.11

BM1 TP2
TP1
Elevation 100.00

Point BS HI FS Elevation
BM1 12.64 112.64 100.00
TP1 10.88 120.41 3.11 109.53
TP2 2.56 117.85
DIFFERENTIAL LEVELING
Computation of Elevations
BS
BS FS 9.72
BS FS 10.88 2.56
12.64 3.11

BM1 TP2
TP1
Elevation 100.00

Point BS HI FS Elevation
BM1 12.64 112.64 100.00
TP1 10.88 120.41 3.11 109.53
TP2 9.72 127.57 2.56 117.85
DIFFERENTIAL LEVELING
Computation of Elevations
BS FS
BS FS 9.72 3.10
BS FS 10.88 2.56
12.64 3.11 BM2

BM1 TP2
TP1
Elevation 100.00

Point BS HI FS Elevation
BM1 12.64 112.64 100.00
TP1 10.88 120.41 3.11 109.53
TP2 9.72 127.57 2.56 117.85
BM2 3.10 124.47
DIFFERENTIAL LEVELING
Computation of Elevations
BS FS
BS FS 9.72 3.10
BS FS 10.88 2.56
12.64 3.11 BM2

BM1 TP2
TP1
Elevation 100.00

Point BS HI FS Elevation
BM1 12.64 112.64 100.00
TP1 10.88 120.41 3.11 109.53
TP2 9.72 127.57 2.56 117.85
BM2 3.10 124.47
DIFFERENTIAL LEVELING
Computation of Elevations
Change in elevation- summation of the backsight and
the foresight then subtract
Point BS HI FS Elevation
BM1 12.64 112.64 100.00
TP1 10.88 120.41 3.11 109.53
TP2 9.72 127.57 2.56 117.85
BM2 3.10 124.47
+33.24 -8.77
Change in elevation = 33.24 -8.77 =24.47
DIFFERENTIAL LEVELING
1. The initial backsight (BS) is taken to a point of
known elevation

2. The backsight reading is added to the elevation of


the known point to compute the height of the
instrument (HI)
3. The level may be moved to a temporary point called a
turning point (TP)
4. The elevation of a point is the height of the
instrument (HI) minus the foresight (FS)
DIFFERENTIAL LEVELING
Computation of Elevations - Group Problem
 Prepare a set of level notes for the survey illustrated
below. What are the elevations of points TP1 and TP2?
BS FS
1.27 4.91 BS FS
BM 2.33 6.17
Elevation 356.68
TP1
TP2
DIFFERENTIAL LEVELING
Computation of Elevations - Group Problem
BS FS
1.27 4.91 BS FS
BM 2.33 6.17
Elevation 356.68
TP1
TP2

Point BS HI FS Elevation
BM1 1.27 357.95 356.68
TP1 2.33 355.37 4.91 353.04
TP2 6.17 349.20
+3.60 -11.08 -7.48
Example
1- Height of instrument method

Back- Height of Inter- Fore- Reduced


Remarks Distance Remarks
sight Instrument mediate sight level
B.M. 0 2.554 52.554 50.00 Datum RL+50 m
A 14.990 1.783 50.771
B 29.105 0.926 51.628
C 48.490 1.963 50591
D 63.540 1.305 50.272 3.587 48.967 change point 1
E 87.665 1.432 48.840
F 102.050 3.250 52.949 0.573 49.699 change point 2
G 113.285 1.925 51.024
H 128.345 3.015 55.468 0.496 52.453 change point 3
J 150.460 0.780 54.688
Sum of B-sight & F-sight,
10.124 5.436 54.688
Difference between RL's

Take smaller from greater -5.436 -50.000


Difference should be equal 4.688 4.688
2- Rise and fall method

Back- Inter- Fore- Reduced


Stations Distance Rise Fall Remarks
sight mediate sight level
B.M. 0 2.554 50.00 Datum RL+50 m
A 14.990 1.783 0.771 50.771
B 29.105 0.926 0.857 51.628
C 48.490 1.963 1.037 50591
D 63.540 1.305 3.587 1.624 48.967 change point 1
E 87.665 1.432 0.127 48.840
F 102.050 3.250 0.573 0.859 49.699 change point 2
G 113.285 1.925 1.325 51.024
H 128.345 3.015 0.496 1.429 52.453 change point 3
J 150.460 0.780 2.235 54.688
Sum of B-sight & F-sight,
Sum of Rise & Fall
10.124 5.436 7.476 2.788 54.688
Take smaller from greater -5.436 -2.788 -50.000
Difference should be equal 4.688 4.688 4.688
H.W. Stations B.S (m) I.S (m) F.S (m) Elevation (m) Remarks
A 0.400 100 BM
B 0.765
C 1.270
D 2.560
E 3.220
F 0.390 3.950 C.P
G 1.690
H 0.800 3.500 C.P
I 1.920
J 2.450
K 3.980

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