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1.1 Introduction
The art of Determining the relative position of an object on the surface of the earth, by taking measurements in the horizontal & vertical planes is known as Surveying. Surveying is Primarily divided into two classes a. Plane Surveying b. Geodetic Surveying
Note: In-plane Surveying the difference in length between the arc and the subtended chord for any two point in the surface of the earth is only about 0.1m for a distance of 18.2km, 0.3m for 54.3km and 0.5 for 91km.
2. General Classification of Surveys The Survey may be classified as the following 4 different ways
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Land Survey is Further Classified as the Following 4 different ways · Topographical survey · Cadastral survey · City survey · Engineering Survey |
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1. Topographical Survey It is carried out for determining natural features of the country such as hill, valleys, mountains, forest, river etc. 2. Cadastral Survey It is carried out to fix the property line (Boundary Line) of Personal, Municipality, Country etc. 3. City Survey It is done for the construction of street, water supply system sewer line small road etc. with in a city. 4. Hydrographical survey It deals with the mapping of large water bodies for the purpose of navigation (bandargaaha) construction of harbor, and determination of mean sea level. It is also known as Marine survey. 5. Astronomical survey It determines the absolute location & absolute direction of heavenly bodies like the sun and moon. 6. Control Survey Establishing the horizontal & vertical positions of widely spaced control points using principles of geodetic surveying. 7. Geological Survey Determining different strata inside the crust. Geologists will be doing this survey.
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Contour in Surveying
An imaginary line, on the ground, joining the point of equal elevation above the assumed datum, is called contour.
Contour interval
· The vertical distance between two consecutive contours is known as contour interval.
· Number of contour line are more in hill as compared to the plains or same contour interval.
· It depends upon SANAPA
· Where, S= scale of map, A= Availability of time and fund, N= Nature of ground, E= extend of survey, P= purpose of map and A= amount of permissible error.
· Contour interval= 20/No of centimeter per km
= 50/No of inches per mile
Contour gradient
· The imaginary line lying throughout on the surface of the earth and preserving a constant inclination to the horizontal.
· It is either rising gradient or falling gradient.
Horizontal Equivalent
· The minimum horizontal distance between two consecutive contours.
· Numerical value of horizontal equivalent in hill is less as compared to the plains.
Interpolation of contours
· Process of drawing contours proportionately between the plotted ground point or between plotted contours.
Method of contouring
1. Direct method
2. Indirect method
1. Direct method:-
· The contour to be plotted is actually traced on the ground only those point are surveyed which happened to be plotted.
· This method is slow and tedious.
· It is generally used for small area and where great accuracy is required.
2. Indirect Method:-
This have three type
1. By squire :- for low undulating area
2. By cross section: for road cannel, railway e t c
3. By tachometric: for high undulating area.
Uses of contour
· Drawing of the section
· Selection and location of road
· Determination of inter-visibility between two points.
· Measurement of catchment area.
· Calculation of reservoir capacity.
#Curve
· A curve may be defined as the regular curve path. The curve may be circular, parabolic spherical and is always tangential to the straight direction and its end.
· Arc:- two dimension
· Arch:- three dimension
· Chord: joining two point of curve
Classification of the curve
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S.N |
Horizontal curve |
Vertical curve |
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1 |
Circular curve |
Summit curve |
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Simple circular curve Compound curve Reverse curve |
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2 |
Transition curve |
Valley curve |
Simple circular curve:
· The curve which consists of a single circular arc as simple circular curve or simple curve.
· It is tangential to both straight portion.
Fig.
Compound Curve:
· A curve consists of two or more arc of different circle with different radii (radius), have in different center but laying on the same side of the common tangent and which bend in the same direction is called compound curve.
· Doesn’t used in Railway Track.
Reverse curve:
· A curve which consists of two arc of different circle of same or different radii (radius) but center of an arc on opposite side is known as reverse curve.
Transition curve:
· A curve of varying radius introduce between straight and circular curve is known as transition curve.
· It provide to reduce effect of centrifugal force of moving vehicle.
· Its ra
· Provided in circular curve and straight portion.
· Rtc=0/ infinity at the junction of straight and transition curve, ending point transition curve or starting in circular Rtc=Rcc, where Rtc= radius of transition curve Rcc= Radius of circular curve.
Element of curve:
· Tangent distance = R Tan Del/2.
· External distance/ Apex distance = R (sec del/2-1)
· Length of curve = pi R del/180
· Mid ordinate = R (1-cos del/2)
· Long cord = 2 R sin del/2
Normal chord:
· The chord between the successive regular peg on the curve is known as Normal Chord
Sub chord:
· When the chord is shorter than normal chord is known as.
· Sub chord generally occurs at the beginning and at the end of curve
Degree of curve
· It may be defined as the central angle of the curve that is substended by an arc of 30m
· Degree of curve = 1718.9/ R or 1720/R (if length is not given this prefer).
· If arc is 20 meter than degree of curve = 1146/R
Chain Survey
· In chain surveying only linear measurements are taken.
· The main principle of chain surveying triangulation. The triangle should be equilaterals.
· Well conditional triangle 30 degree to 120 degree. Ill-conditional triangle less than 30 degree and greater than 120 degree.
· The triangle should not have any angle smaller than 30 degree and greater than 120 degree is known as well conditional triangle. Otherwise Ill conditional triangle.
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Suitability |
Unsuitability |
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· Small area · Fairly level ground · Open area
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· Large area · Undulating, broken and steep. · Congested area like forest city town etc. |
Important points
Base line:
· The longest line in whole survey area of main survey line is called.
· Various survey station are plotted with reference to the base line.
· Normally it is measured with chain
Check line
· The line which run in the field to check accuracy of field work.
· It is also known as proof line.
· Each triangle must have check line.
Tie line
· Distance between chain lines to site is known as offset line.
· The line joining the two subsidiary station on main chain line is called.
· The main purpose of tie line is to reduces or avoid the long offsets from the main chain line
· It also used for the accuracy of work.
· To locate interior details which are far apart from a main chain line.
Important Note
· The points where two sides of main triangle meet is called main survey stations.
· The line joining the main survey station is called main survey line.
· The stations which are selected on main survey line is called tie stations/ subsidiary stations.
· Main stations are plotted by Small triangle with capital letter.
· Tie stations are plotted by small circle with small letter.
Offsets
· Lateral measurement for locating the position of details.
· Two types of lateral measurement
1. Perpendicular offset:
· Offset are right angle to the survey line
2. Oblique offset
· The measurement which are not made right angle but is inclined is called.
· If the length of offset is less than 15 m are called short otherwise long offset.
· Offset is not greater than 20m
Obstacles in chaining
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S.N. |
Condition |
Example |
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1 |
Obstacle in ranging but not chaining |
Hill rock |
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2 |
Obstacle in chaining but not ranging |
River and pond |
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3 |
Obstacle in both ranging and chaining |
Tall building |
Right angle instruments
Cross staff:
1. Open cross staff:- used for measuring 90 degree
2. Adjustable cross staff:- used for measuring 90 degree
3. French cross staff: - used for measuring 45 and 90 degree.
Optical squire
· More accurate than cross staff
· Generally used for measuring long offset
· It is based on the double reflections.
· Principle of optical squire reflection.
1. In chain surveying accuracy depends upon the follower.
2. Accuracy of measurement in plotting up-to 0.25 mm to that of measurement (1 in 250)
3. Permissible error in chain survey is 1 in 250.
Compass Survey
· Measured direction of survey line by means of compass and distance are measured by tape or chain.
· This survey is suitable for those where the magnetic effect is least or none.
Difference between prismatic compass and surveyor compass
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Prismatic compass |
Surveyor compass |
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· Fig · Inverted 0-360 degree 0 degree at South end and clockwise. · Whole circle bearing system · Tripod is not essential |
· Fig · Erect 0-90 degree, 0 degree at both North and south pole · Reduced/qudrantal bearing system · Tripods is very essential |
Whole circle bearing and reduced bearing
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Whole circle bearing |
Reduced bearing |
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· Always measured from North pole · Running clockwise direction. · Fig
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· Measured from North and South Pole. · Either clockwise or Anti clockwise whatever. · N angle E,N angle W and S angle , S angle W · Fig |
Fore Bearing and Back Bearing
Note BB=FB +_ 180 degree when FB is less than 180 Degree than plus sign is used and when it exceed 180 degree negative sign is used.
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Fore Bearing |
Back Bearing |
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· Bearing in the direction of the progress of survey work is called. · |
· Bearing in the opposite direction of survey work is called. · |
Terms used in compass surveying
1. Magnetic compass:
· The samaller horizontal angle between TM and MM is called.
· TB=MB+_ Declination
· If + is East
· If _ is west
2. Azimuth
· The smaller horizontal angle between TM and survey line
3. True bearing
· If the bearing of any survey line is measured from true meridian is called true bearing.
4. Magnetic bearing
· If the bearing of the any survey line is measured from MM is called MB.
5. Deep
· It is the inclination between the longitudinal axis of magnetic needle and the horizontal plane through its pivot.
· It is vertical angle whose value vary from place to place.
· It is zero at equator and 90 degree at pole
Temporary adjustment of compass
· Centering
· Levelling
· Focusing the prism
Types of line in compass
· Agonic line: the line joining the point of Zero declination is called.
· Isogonic line: the line joining the points of equal declination is called
· Isoclinic line : the line joining the equal deep is called