Chapter #1: Basics of Surveying

1.1 Surveying Defined What is surveying? Surveying is the art of measuring distances, angles and positions on or near the surface of the earth. . .

The primary aims of field surveying are : To measure the horizontal distance between points.   To measure the vertical elevation between points.   To find out the relative direction of lines by measuring horizontal angles   To find out absolute direction by measuring horizontal angles with reference to fixed direction. These parameters are utilized to find out the relative or absolute coordinates of a point / location.

Discussion abt Importance of surveying Objectives of surveying Types of surveying Classifications of surveying Principles of surveying Surveying measurements

Objects of survey Plan: When the area is surveyed is small and the scale to which its result plotted is large, then it is known as plan. Scale : 1:100,1:200,1:500 ,etc. E.g.: a plan of a building

Map: When the area surveyed is large and the scale to which its result plotted is small, then it is known as Map Scale : 1:10000,1:100000,etc E.g. : Map of India

1.2 Types of Surveying Plane surveying Geodetic surveying There are two types of surveying: Plane surveying Geodetic surveying

Plane surveying The surveying in which earth surface is assumed as a plane and the curvature of the earth is ignored is known as plane surveying . As the plane survey extends only over small areas, the line connecting 2 points is considered as a straight line and the angle b/t any 2 lines is considered as plane angle .

Geodetic surveying The surface of the earth is not plane but spheroidal. Therefore, the line connecting any two points on the earth’s surface is not a straight line but a curve . The surveying in which curvature of the earth is taken into account for all measurements is known as geodetic survey. It possess a high degree of accuracy . It is also called trignometrical surveying.

Classifications of surveys 1. Based upon the nature of the field 2. Based upon the method 3. Based upon the instruments used 4. Based upon the objective of survey

1.Based on the nature/ place of survey Land survey –city survey,engg survey, topographic ,cadastral survey Hydrographic survey Under – ground survey Aerial survey

2.Based on the method Triangulation survey Traverse survey Closed Open traverse traverse

3. Based on the instruments used Chain survey Compass survey Plane table survey Theodolite survey Tacheometric survey

4. Based on the purpose/objects of survey Engineering survey Defence survey Geological survey Mine survey Geographical survey Archeological survey Route survey

Principles of survey Working from whole to part Fixing new points by at least two independent process

Working from whole to part This is being achieved by establishing a hierarchy of networks of control points. The less precise networks are established within the higher precise network and thus restrict the errors. To minimize the error limit, highest precise network (primary network) figure 1.1 of control points are established using the most accurate / precise instruments for collection of data and rigorous methods of analysis are employed to find network parameters. This also involves most skilled manpower and costly resources which are rare and cost intensive.

Working from whole to part

The purpose of working from whole to part is To localize the errors and To control the accumulation of errors.

Fixing new points by at least ‘2’ independent process The reference of any point, say X, has to kept with respect to, at least, two permanent objects or well defined points, say Y and Z. Generally, this has been achieved by taking measurement of two parameters. The location of a point, say X can be done as shown in the figure below. (a) Distances YX and ZX (Figure 1.2)

(b) Perpendicular distance OX and distance OY or OZ (Figure 1.3)

(c) Distance YX or ZX and angle YZX or ZYX (Figure 1 (c) Distance YX or ZX and angle YZX or ZYX (Figure 1.4(a))and (Figure 1.4(b))

(d) Angles YZX and ZYX. (Figure 1.5) The point of intersection of the two measured parameters defines the position of the point.

Measurements of distances Direct method –tapes ,chains Computative method – tachometry, triangulation, etc

Instruments used in chain surveying Instruments for Measuring Horizontal Distance 1) Chain or tape 2) Arrows Instruments for Marking Stations on the Ground 3) Ranging rods 4) Cross staff 5) Offset rods 6) Pegs 7) Plumb bob 8)Field book

DESCRIPTION a) Chain: The chain is composed of 100 or 150 pieces of galvanized mild steel wire, 4mm in diameter called links . The ends of each link are bent into a loop and connected together by means of three oval rings. The ends of the chain are provided with handles for dragging the chain on the ground, each wire with a swivel joint so that the chain can be turned without twisting. The length of the chain is measured from the outside of one handle to the outside of another handle. Tallies are fixed at every five-meter length and brass rings are provided at every meter length except where tallies are attached

Following are the various types of chain in common use: 1) Metric chains 2) Gunter’s chain or surveyors chain 3) Engineers chain 4) Revenue chain 5) Steel band or Band chain

Merits and demerits of a chain It is often preferred for rough use and for ordinary works It can be read easily Due to its heavy weight , the chain is often subjected to sagging which leads accuracy of measurements

2. Arrows: Arrows are made of good quality hardened steel wire of 4 mm diameter. The arrows are made 400 mm in length, are pointed at one and the other end is bent into a loop or circle

3. Ranging rods: Ranging rods are used for marking the positions of stations and for ranging the survey lines . The length of the ranging rod is either 2m or 3m long with a heavy iron point 150 mm long at the lower end. Ranging rods are divided into equal parts 0.2m long and they are painted alternately black and white or red and white or red, white and black.

4. Cross staff: The simplest instrument used for setting out a right angle. The common forms of cross staff are: Open cross staff, French cross staff, Adjustable cross staff

5. OFFSET ROD: The offset rod is used for measuring the off set of short lengths. It is similar to a ranging rod and is usually of 3m lengths.

BOB 6. PEGS: These are rods made from hard timber and tapered at one end, generally 25mm or 30mm square and 150mm long wooden pegs are used to mark the position of the station on. 7. PLUMB BOB: While chaining along sloping ground, a plumb bob is required to transfer the points to the ground.

Principle of chain surveying The principle of chain surveying is to divide the area into a number of triangles of suitable sides . A network of triangles is preferred here as triangle is the simple plane geometrical figure which can be plotted with the lengths of its sides alone. In this case, there is no need for measuring angles

Suitability of chain surveying It is suitable when the ground is fairly level and open with simple details. When large scale plans are needed , this type suitable It is suitable when the area to be surveyed is comparatively small in extent It is suitable for ordinary works as its length alerts due to continued uses Sagging of chain due to its heavy weight reduces the accuracy of measurements It can be read easily and repaired in the field itself It is suitable for rough usage

Unsuitability of chain survey It is unsuitable for large areas crowded with many details It is unsuitable for wooded areas and undulating areas

Technical terms Main station: It is point in chain survey where the two sides of a traverse or triangle meet (A,B,C etc ) Subsidiary station: It is a station on the survey line joining two main stations (a,b,c, etc) Main survey line A line joining two main stations is called main survey line (AB,BC,etc).

A B a b c well d C F G D E

Tie line The line joining two subsidiary stations is known as tie line (ac,cd,etc) and it is otherwise called subsidiary line Base line It is the longest main survey line and passing through the centre of the area . Check line This line is very much essential to check the accuracy of the field work .(ad)

Offset The perpendicular (or) the oblique distance of the object from the survey line is called an offset .

PRISMATIC COMPASS The graduated ring remains stationary as it is attached to magnetic needle. While the compass needle and the eye sight vane can be rotated The graduations are made in such a way that 00 or 3600 is at the south, 1800 at north, 900 at south and 2700 at east Sighting of the object and the taking of reading is done simultaneously Prismatic compass can be used without a tripod SURVEYORS COMPASS The graduated ring being attached to the compass moves with sights. But needle remains stationary when box is rotated The graduations are made as 00 at north & south 900 at east and west. The east and west positions are interchanged in order to read the bearing in quadrantal bearing system Sighting the object is done first. Then the reading is to be taken with naked eye by looking above the needle point Surveyor's compass cannot be used without a tripod

1.3 Classes of surveys Preliminary survey: (data gathering ) is the gathering of data (distances, position and angles) to locate physical features (rivers, roads, structures) so that data can be plotted to scale (map or plan), also include diff. in elevation so that contour could be plotted.

Layout survey: Marking on the ground using sticks iron bar or concrete monuments. The features shown on a design plan features: - Property lines (subdivision survey). - Engineering work (construction survey). - Z-dimensions are given for x-y directions. Control survey: used to reference prelim and layout surveys. Horizontal control: arbitrary line tied to prop line or HWY center or coordinated control stations.

Vertical control: Benchmarks: points whose elev Vertical control: Benchmarks: points whose elev. above sea level is carefully determined. - In Control survey more care to accuracy. - Control lines should be easy to re-establish.

1.4based on the nature of field of surveying 1- Topographic survey: preliminary surveys used to tie earth surface features. 2- Hydrographic survey: preliminary surveys tie underwater feature to surface control line 3- Route surveys: preliminary, layout and control surveys that range over a narrow but long strip of land (highways, railroads, electricity transmission lines and channels).

4- Property surveys: preliminary, layout and control surveys determine boundary locations for a new map. 5- Aerial survey: preliminary and final surveys convert aerial photograph into scale map using photogram metric tech. 6- Construction survey: layout of engineering work. 7- Final (as built) survey: preliminary surveys tie in features that just have been constructed

1.5 Surveying Instrument 1- Transit and theodolite: Establish straight or curved lines, horizontal and vertical angles. 2- The level and rod: measure difference in elevations. 3- Steel tape: measure horizontal and slope distances. 4- Total station. 5- GPS (global positioning system) receivers.

Steel tape Level ( stadia principle ) Total station Thedilite GPS

1.6 Survey Geographic Reference Define reference as the surface of earth. Latitude: East/West //equator. - Max angle 90o north or south. Longitude (Meridians): North/South converge at poles & max angle = 180 degree east or west from the plane of 0o longitude Greenwich. - used in geodetic not plane survey. - Plane survey use coordinates grid system.

1.7 Survey Grid Reference States and provinces have adopted a grid system best suited to their needs. - Limited in size: no serious error due to curvatures. - Easy to use (plane geometry & trigonometry). - Common datum for x & y dimensions. - Easy to translate to geodetic survey.

1.9 Survey Vertical reference Vertical dimension can be referenced to any datum. - Mostly used datum is mean sea level MSL = 0.000 ft. - Benchmarks  permanent points whose elevation has been precisely determined.

1.10 Distance Measurements Distance between two points can be horizontal, slope or vertical and are recorded in feet (foot units) of meters (SI units). - Horizontal and slope distances can be measured by using fiberglass, steel tape or EDM (electronic distance measuring) + difference in elevation and slope distance. - Vertical distance can be measured by using tape as in construction work or level and leveling rod

1.11 Unit of Measurement There are two main measuring systems: English system and Metric system (SI units). - All countries will change to Metric system. - Angles are measured by: Degrees, minutes and seconds. - 1 revolution = 360 degrees, 1 degree = 60 minutes and 1 minutes = 60 seconds.

1.12 Location Methods - (a): right angle offset tie. B B B P P P C A A A - (a): right angle offset tie. - (b): the angle distance tie (polar tie). - (c): angle at A and B of distance BP of AP (intersection technique).

1.13 Accuracy and precision Accuracy: relationship between measure & true value of measurement. Precision: Degree of refinement with which the measurement is made. Example: True Distance Measured Distance Error Cloth tape 157.22 157.3 0.08 Steel tape 157.22 157.23 0.01 - More precise method resulted in more accurate. - More precise method may result in less accurate measurement. Example: Repaired tape.

1.14 Accuracy Ratio Error of closure: The difference between the measured location and the theoretical correct location (repeated measurement, mathematical analysis). Exp. measured distance 250.56 errors 0.06 Known distance 250.50 Accuracy ratio 0.06/250.50 = 1/4175 = 1/4200 - Fraction whose numerator is unity and denominator closest 100 unit.

1.15 Errors - No measurement (except count) can be free of error. True value is determined statistically (mean) to calculate error. Systematic error: error whose magnitude and algebraic sign can be determined and eliminated (temp. error). Random Error: - Error due to surveyor skill. - Tend to cancel each other. - Little significance except for high precision survey. - Unskilled or careless surveyor can make problem. - Large random error doesn’t result in accurate work even if they cancel.

1.16 Mistakes There are many mistakes that cold be happened to surveyors. - Blunders made by survey personnel e.g. 68 instead of 86. - Miscounting tape length, measuring from wrong point. - Mistakes will occur and must be discovered and eliminated by verifying the measurement (Repeat Geometry analysis, etc.). - Every measurement should be repeated to eliminate mistakes and improved precision.

1.17 Stationing Along Baseline: stations or champagne At night angle: offset dist. Beg. 0+00 ft (m). 0+00 2+50 4+96 5+43.12