2. Surveying
Fundamentals of surveying; measurements (linear distance, vertical distance, and angle
and directions); topographic survey (principles and applications); principles and
applications of GPS/GIS;
3. Surveying
Surveying is the science of determining relative positions of objects on the surface of
the earth by taking measurements of distance, directions and elevations and plotting
them to convenient reduced sizes on paper.
The object of surveying is to prepare a map or plan to show the relative positions of
the objects on the surface of the earth.
The map or plan is drawn to some suitable scale
4. Principles
• Locating a point on the surface of the earth by at least two reference points.
• Working from whole to part (prevent from cumulating of ends and localized minor
errors).
• Consistency in work
Consistency in methods, instruments, reading, noting.
• Independent check
Every measurement can be re-checked by different field test.
5. Classification of Survey
1. Based on culture of earth.
a) Plane survey
• The Curvature of the earth is ignored
• Line joining any two stations is considered to be straight
• Survey covering an area up to 260 km2.
• The difference for 18.2 km is only 0.1 m.
b) Geodetic survey:
• The curvature of earth is taken into account.
• The line joining any two stations is considered as spherical.
• It is carried out covering area above 260 km2.
• It is mainly used for establish control points for plane survey.
6. Classification of Survey
2. Based on nature of field:
a) Land survey.
Topographic survey is used to indicate the natural features while cadastral survey is
use for fixing property line.
b) Hydrographic survey:
Carried out for studies of large water bodies.
c) Astronomical survey
It is used to determine absolute locations on surface of earth by making observations
of heavenly bodies.
7. Classification of Survey
• Plan is graphical representation of the features of the earth, projected on horizontal
plane and it does not show it geographical positions on globe.
• Map is represented in small scale than plan and shows its geographical position on
the globe
8. Instruments for measuring distances
1. Tape.
a) Cloth or linen tape– (10 – 30) m length and (12 – 15) mm width.
Used for offset measurement and rarely used for making accurate measurement.
b) Metallic tape– A linen tape reinforced with brass or copper wires to prevent
stretching or twisting fibers is called metallic tape.
– Normally used for taking offset.
c) Steel tape– measures distances more accurately than metallic and linen tape.
d) Invar tapes (steel 64% and nickel 36%) – Used mainly if high degree of precision is
required.
– Available in 3 m length.
9. Instruments for measuring distances
2. Steel bands– are used where high accuracy is required.
– It is 20 m or 30 m long and 16 mm wide.
3. Chain
a) Engineers chain– 100 feet long– divided into 100 lines.
b) Gunter’s chain– 66 feet long– divided into 16 links.
c) Revenue chain– 33 feet long– divided into 16 links.
d) Metric chain– 20 meters (divided into 100 links) and 30 meters (divided into 150
links)
– The handle of chain is made of brass and is included in whole length of chain.
– The hundreds of chain has swivel joint to provide flexibility.
– Links are made from 5 mm diameter galvanized mild steel wire.
10. Instruments used in Surveying:
a) Arrows– Each chain is accompanied with 10 arrows.
b) Iron pegs– Used in hard ground surfaces.
c) Ranging rods– (2 m or 3m) in height, 3 cm nominal diameter, alternatively pointed of
height 0.2 m.
d) Ranging poles– Similar to ranging rods except height (4 –6) m.
e) Offset rods– Similar to ranging rods except top is provided with hook for pulling or
pushing a chain through obstruction.
f) Plumb bob– It is 50 mm long and weight varies iron 2 to 5 N.
g) Line ranger– It is a small reflecting instruments used for fixing intermediate points on
the chain lines.
11. Ranging of line:
a) Direct ranging– when intermediate ranging rods are fixed along the chain line by
direct observations from either end station is called as direct ranging.
b) Indirect ranging– When end stations are not visible, ranging is done by reciprocal
ranging or by running an auxiliary line is called indirect ranging.
– Minimum 4 ranging rod is required.
c) Random ranging– Stations are neither visible from end paints nor intermediate
points, then random ranging is carried out.
12. Chaining of sloping grounds:
a) Direct method/steeping method
• more convenient and gives better results while measuring to horizontal distance
down the hill.
• Drop arrow is used
b) Indirect method:
• more accurate and rapid when the slope of the ground is long and gentle.
• By measuring slope and angle of slope.
Angle of slope is measured by clinometers or abney level.
While surveying proceed up hill rather down hill.
Chaining is adopted if fall is not greater than 1.8 m.
13. Chaining
• Chain survey is suitable when.
a) Ground is fairly level and open with simple detail
b) Plans are required on large scale.
c) Area to be surveyed is small.
– Principle of chain survey is triangulation.
– Well condition triangle no angle less than 30° or greater than 120°
14. Instruments for setting out right angles
1. Cross-Staff.
a) Open cross– staff (90°)
b) French cross– staff (45° or 90°), have 8 faces.
c) Adjustable cross-staff – setting out an offset at any angle.
2. Optical square.
– More accurate than cross-staff and used for setting out accuracy the long offsets.
– It is based upon the principal of reflection
15. Obstacles in chaining
• Obstacles in ranging but not in chaining i.e. chaining free, vision obstructed-rising
ground, hill rock.
• Obstructed in chaining but not in ranging: vision free-pond, plantations, river etc.
• Obstacle in both ranging and chaining-building.
16. Errors in chaining
• Instrumental errors– these are errors due to faulty adjustments or imperfections of
instruments such as chain or tape may be too long or too short etc.
• Natural errors– These errors arises due to variations in the phenomenon of nature
such as temperature etc.
• Personal errors– These errors are classified as compensatory errors and cumulative
errors.
• Compensating errors are those which occur in either directin and tend to
compensate at the end and can not be corrected easily but can be corrected only
using law of probability(dispersion theory)
17. Errors in chaining
• Cumulative /systematic errors are those which occur in one direction only and go on
accumulating and can be corrected for eg. Length of chain shorter or longer than
standards length, slope correction errors, ranging not in straight line etc. such errors
produces same sign and size. Such type of error can be avoided by calibration.
• The compensating and cumulating errors that occur in chaining are proportional to
under root of length
• Accidental errors– Errors due to carelessness.
It is proportional to square root of the number of observation taken.
18. Practice Question
1. An instrument used for ranging is called
a. optical square b. line ranger c. clinometers d. pedometer
2. Indirect ranging is adopted when the two ends of chain line are
a. mutually invisible b. too distant
c. on a sloping ground d. separated by a valley
3. Indirect ranging is adopted when the two ends of chain line are
a. mutually invisible b. too distant
c. on a sloping ground d. separated by a valley
4. Indirect ranging is adopted when the two ends of chain line are
a. mutually invisible b. too distant c. on a sloping ground d. separated by a
valley
19. Compass Surveying
If the area is large, with undulations compass survey is adopted.
Bearing of a line is its direction with respect to reference line i.e. meridian.
• The inclination of the needle with the horizontal is known as dip of the needle, dip
angle is ‘0’ at the equator and 90 degree at pole
• Angle of dip is vertical angle.
• Magnetic declination is the horizontal angle between the true meridian and
magnetic meridian. If the magnetic meridian is to be positive and if it is to the left
side (western side) the declination is said to be negative.
• An imaginary line drawn through the points of same declination is called isogonic
line.
• A line joining same angle of dip is isoclinic lines.
• Line joining the points of zero declination is called agonic lines.
• Azimuth is the smaller angle which, survey lines makes with the true bearing
20. Compass Surveying
• Deflection angle is the included angle between the prolongation of previous line and
succeeding line.
• Clockwise deflection is called right deflection and it is additive where anticlockwise
deflection is left deflection and is subtractive.
• The algebraic sum of deflection angle is 360°
• In a closed traverse.
• Sum of internal angles = (2n – 4) × 90°
• Sum of external angles = (2n + 4) × 90°
21. Types of compass and are mostly used.
Item Prismatic compass Surveyor’s compass
– Bearing
– Graduations
W.C.B.
0° at south, 90° at west, 180°
at north, 270° at east.
Inverted
LC is 15’
R.B.
0° at north and south
90° at east and west
Erect
No of zero graduation is 2
– Needle Broad type–fitted to the
bottom of float along with
broad type magnet
Edge bar type-Attached to the
box.
– Tripod Not required required
22. Designation of bearing
a) While circle bearing (W.C.B.)
– It is also called as azimuthal bearing.
– Prismatic compass or a Theodolite is observed in W.B.C.
b) Quadrantal bearing system (Q.B)
– Bearing of line is measured clockwise or anticlockwise from north and south.
– Surveyors compass is graduated in Q.B.
– Back bearing = Fore bearing 180° (+ve if FB is <180° and (– ve is F.B. > 180°)
– Traverse in compass survey may be open or closed.
23. Designation of bearing
a) While circle bearing (W.C.B.)
– It is also called as azimuthal bearing.
– Prismatic compass or a Theodolite is observed in W.B.C.
b) Quadrantal bearing system (Q.B)
– Bearing of line is measured clockwise or anticlockwise from north and south.
– Surveyors compass is graduated in Q.B.
– Back bearing = Fore bearing 180° (+ve if FB is <180° and (– ve is F.B. > 180°)
– Traverse in compass survey may be open or closed.
24. Leveling
• It is the process of determining relative elevations of places with respect to a datum line.
• A level surface is a surface parallel to the mean spheroidal surface of earth.
• Principle of leveling is based on principal of optical phenomenon.
• Level line: A line lying in the level surface is known as a level line.
• Level surface: Every point on this surface is equidistant from the centre of earth. It is normal to plumb line
at all stations. Level surface is a curved surface e.g. the surface of still water in the lake.
• Horizontal surface: A surface tangential to the level surface at a point is known as horizontal surface. It is
always perpendicular to the plumb line.
• Horizontal line– Line lying in horizontal surface is called horizontal line and it is tangential to the level line.
• Vertical surface: A vertical surface through any point is a surface normal to the level surface is called
vertical line and is normal to the level line.
• Elevation of a point: It is a vertical distance above or below the datum and also called as reduced level.
(R.L.)
25. Leveling
• Bench mark: It is fixed reference point of known elevation. B.M includes Great Trigonometrical Survey
(GTS), Permanent B.M, Temporary B.M and arbitrary B.M. GTS B.M is most accurate and placed in interval
of 100 Km.
• Back sight: It is a staff reading taken on a point of known elevation as on a B.M. or C.P. It is the first staff
reading taken after the level is set up and leveled. It is also called a plus sight.
• Fore sight: It is a staff reading taken on a point whose elevation is to be determined as on a change point. It
is the last staff reading taken before shifting an instrument. It is also called as a minus sight.
• Change point: It is point denoting the shifting of the level and point where B.S. and F.S. are taken.
• Station: It is a point where staff is held and whose elevation is to be determined.
26. Reduction of levels
a) Collimation or height of instrument method:
– B.S. – .F.S. = last R.L. – first R.L.
– There is no check on R.L. of intermediate sights.
– Generally used in profile leveling and in setting out levels for constructed work.
b) Rise and Fall method:
– .B.S. – .F.S. – Rise – Fall – Last R.L. – First R.L.
– There is check of R.L. of I.S.
– This method is used for differential leveling and other precise leveling operations.
– It is preferred where less number of intermediate stations are exist.
27. Correction for curvature and refraction:
• Curvature makes the objects ‘lower’ than they really are.
• Refraction makes appears the objects ‘higher’ than they really are.
• Correction for curvature is – ve and that of refraction is + ve.
• Curvature correction (Cc) = 0.0785 d2 metres (– ve), where‘d’ is km
• Refraction correction (Cr.) = Cc = 0.0112 d2 (+ ve).
• Combined correction due to refraction and curvature is 0.0673d2 m (– ve).
28. Principles and applications of GPS/GIS
GPS
• GPS Stands for Global Positioning Systems and they are now used throughout the world.
A GPS unit is actually a receiver that collects signals from satellites.
• It is a system of earth-orbiting satellites which provides a precise location on earth’s
surface in latitude/longitude coordinates.
GIS
• A geographic information system (GIS) is a computer-based tool that examines spatial
relationships, patterns and trends.
• It is used for capturing, storing, checking, and displaying data related to positions on
Earth’s surface.
• It is an organized collection of computer hardware, software, and geographical data to
analyze and display all forms of referenced information.
29. Practice Questions
1. The object of surveying is to prepare a:
a. Map b. Cross-section c. Drawing d. Model
2. The main principle of surveying is to work from:
a. The part to the whole. b. The whole to the part.
c. The centre to the boundary d. The boundary to the centre
3. The error in measured length due to incorrect holding of chain is
a. Compensating errors b. cumulative errors c. instrumental error d. negative error
4. ln chain survey the area is divided into :
a. Circle b. Square c. Triangles d. Rectangular
5. The correction for sag is
a. always additive b. always subtractive
c. always zero d. sometimes additive and sometimes subtractive
30. Practice Questions
1. Leveling should always commence from a:
a. Leveled ground. b. Bench mark. c. Permanent point. d. Highest point.
2. If the floor level of the building is at R.L of 100 m , back sight reading is 1.25 m and reading of staff
kept at ceiling is 2.25, then upper floor level of building is
a) 96.5 b) 99 c) 101 d) 103.5
