same Engineering Series / / | |Fundamental Concepts 1.1 INTRODUCTION Surveying is one of the oldest arts practised by man. History reveals that the principles and practices of surveying were used, consciously or unconsciously, even in the primitive ages, albeit in a crude manner. In the past few decades, however, these have become more rational and channelised. The introduction and practice of surveying is indispensable to all branches of engineering. The training that a student receives, irrespective of his branch of engineering, in the art of observing, recording, and computing data, as well as in the study of errors their causes and effects, directly contribute to his success in other professional courses. He develops inter alia such qualities as self-reliance, initiative and the ability to get along with the others. This also helps an engineer get acquainted with the reasonable limits of accuracy and the value of significant figures. A knowledge of the limits of accuracy can best be obtained by making measurements with the surveying equipment employed in practice, as these measurements provide a true concept of the theory of errors. An engineer must also know when to work to thousandths, hundredths or tenths of a metre and what precision in field data is necessary to justify carrying out computations to the desired number of decimal place. With experience, he learns how the funds, equipments, time, and personnel available will govern the procedure and the results. Taking field notes under all sorts of field conditions trains a person to become an excellent engineer, capable of exercising independent judgements. Surveying is of special importance and interest to a civil engineer. Surveys are required prior to and during the planning and construction of buildings, dams, highways, railways, bridges, canals, tunnels, drainage works, water supply and sewerage systems, etc. They may also be required for planning and construction of factories, assembly lines, jigs, fabrications, missile ranges, launch sites, and mine shafts. Surveying is the starting point for any project or constructionalscheme under consideration. Details of the proposed work are plotted from the field notes. The reliability of the estimation of quantities and the effectiveness of the design depends upon the precision and thoroughness exercised during the survey. Today, the art of surveying has become an important profession. An introduction to the principles and practices of surveying is, therefore, desirable as an integral part of engineering education and training, irrespective of the branch of specialization. A knowledge of surveying trains the ability of engineers to visualize, think logically and pursue the engineering approach. It promotes a feeling of confidence, a habit of working in groups, neatness and care in documentation, and begin interpersonal relations by the way of simultaneous and tactful handling of clients. For a better understanding of the discussions to follow, brief definitions of a few important terms as applied in surveying are presented. 1.2. DEFINITIONS The Earth Surface The earth is not a true sphere and a slightly flattened at the poles. Its polar axis is somewhat smaller in length (about 43.45 km) than that of its equatorial axis. Any section of the earth parallel to the equator is a circle and any of its section parallel through the poles is an ellipse. Such a figure may be generated by revolving about its minor axis and is called an oblate spheroid. Precisely, the equatorial section is also slightly elliptical and therefore such a figure should be called an ellipsoid. Precise observations indicate that the southern hemisphere is a trifle larger than the northern. Therefore, all the polar sections are oval and can be called ovaloid. In fact, no geometrical solid represents the true shape of the earth. The earth is also recognized by a new name, geoid. However, for all measurement purposes in surveying, the irregularities of the earth’s surface, as discussed above, may be assumed to be absent and the resultant surface be considered a spheroid. Level Surface A level surface is a curved surface, every point on which is equidistant from the centre of the earth and every surface element is normal to the plumb line. It is parallel to the mean spheroidal surface of the earth. However, for plane or ordinary surveying, a level surface at any point is assumed to be a plane surface perpendicular to the plumb line at that point. The particular surface at the average sea level is known as mean sea level. Greot Circle Imagine a plane passing through the centre of the earth (Fig. 1.1). The intersection of such a plane with the mean level surface of the earth is termed as the great circle of the earth.Meridian Itis the line defined by the intersection of an imaginary plane, pass- ing through the poles and any point on the earth’s level surface, e.g. A (Fig. 1.2). Fig. 1.2 Plumb Line The plumb line is normal to the meridian, Considering the mean level surface of the earth as spherical, these lines converge at the centre of the earth (Fig. 1.3). (Note Earth being an oblate spheroid, the perpendiculars to the surface do not converge at any point. The irregular distribution of the earth's mass also causes some deviations. But for plane surveying, all such deviations are ignored and plumb lines are assumed to converge at the centre of the earth. NPL ‘A Fig. 1.3 Polar axisLevel Line Any portion of the line lying on the great circle of the earth is called a level line. It may also be defined as a line lying on the level surface and normal to the plumb line at all the points. Horizontal Plane and Line A plane through any point on the earth's mean level surface and tangent to the surface at that point is known as horizontal plane. A line lying in the horizontal plane is termed as horizontal line. Through any point on the earth’s surface, there can be only one horizontal plane but infinite horizontal lines. Vertical Plane and Line A line through a point perpendicular to the hori- zontal plane is called a vertical line. A plane passing through that point and containing the vertical line is termed as vertical plane. Through any point on the earth’s surface, there can be only one vertical line but infinite vertical planes. Spherical Triangle Imagine three points A, B and C (Fig. 1.4) on the mean level surface of the earth. The three points when joined form a triangle having a curved surface ABC, and AB, BC and CA being the arcs. The triangle ABC is known as a spherical triangle and the angles A’, B’ and C’ are spherical angles. The amount by which the sum of the angles of a spherical triangle exceeds by 180° is called spherical excess. Fig. 1.4 Spherical triangle Grade It is defined as the slope of a line. It is also called gradient. Elevation It is the vertical distance of a point above or below the reference surface (datum). When elevations are with respect to the earth’s surface, the datum is the mean sea level. The datum is a curved surface and, therefore, its curvature should be given due consideration even while determining elevations in plane surveying. An imaginary line joining points of equal elevations is known as contour. 1.3 SURVEYING It is defined as an art to determine the relative positions of points on, above or beneath the surface of the earth, with respect to each other, by measurements of horizontal and vertical distances, angles and directions.A person performing operations to obtain such measurements is known as a surveyor. In his day-to-day work, a surveyor deals with a very small portion of ‘the earth’s surface, However, he is the best judge with regard to the earth’s surface as plane or curved depending upon the character, magnitude of the work and the precision desired. The purpose of surveying is to determine the dimensions and contours of any part of the earth’s surface, i.e. to prepare a plan or map, establish boundaries of the land, measure area and volume, and select a suitable site for an engineering project. Both plans and maps are the graphical representations of the features on a horizontal plane. The former is a large-scale representation whereas the latter is a small-scale one. When the topography of the terrain is depicted on map with contours and spot levels, etc., it is called a topographic map. Scale is defined as the fixed proportion which every distance between locations of the points on the map bears to the corresponding distances between their positions on the earth’s surface. Primary considerations in choosing the scale for a particular project are those to which the map will be put and the extent of the territory to be represented. For most of the engineering projects, the scale varies from 1 cm = 2.5 -100 m. Frequently, the choice of the scale is Testricted to some scale small enough so that the whole map will fall within a Tectangle of a given size, the dimensions of which are determined by the size of blue print frame, or by the size of sheet most convenient for handling. The fol- lowing rules may be observed in deciding the scale. 1. Choose a scale large enough so that in plotting or in scaling distances from the finished map it will not be necessary to read the scale closer than 1/100. 2. Choose as small a scale as is consistent with a clear delineation of the smallest detail to be plotted, due regard being paid to rule 1. A scale may be represented numerically by engineer’ s scale or representative fraction. The engineer's scale is represented by a statement, ¢.g., 1cm= 40m. When a scale is represented by a fraction whose numerator is invariably unity, it is called a representative fraction. In forming the representative frac- tion, both the numerator and the denominator must be reduced to the same de- nomination. For a scale of 1 cm = 1 km, the representative fraction is 1/100,000. The representative fractions and scales recommended for various types of maps are as follows: Type Representative Scale Fraction (R.F.) Geographical map 1; 16000 000 lcm = 160 km Topographical map 1: 250 000 lom = 2.5 km Location map 1; 500 to 1 : 2500 1m = 5-25 m Forest map 1:25 000 lcm = 0.25 km (Contd.)Type Representative Scale Fraction (R.F.) Cadastral map 1: 1000 to 1: 5000 lcm = 10-50 m ‘Town planning 1: 5000 to 1: 10000 Tem = 50-100 m Buildings 1: 1000 lem=10m Mines 1: 1000 to 1: 25000 lcm = 10-25 m Preliminary survey of 1: 1000 to 1 : 6000 Tem = 10-60 m Tails and roads Another most suitable method used to represent the scale of a map is the graphical scale. It is a line drawn on the map so that its distance on the map corresponds to a convenient unit of length on the ground. Figure 1.5 shows a graphical scale corresponding to a scale of 1 cm = 5 m. A 12 cm long line, divided into six equal parts of 2 cm each, is drawn on the map. Thus, each part represents 10 m on the ground. The first part is divided into 10 equal divisions, each representing | m. Figure 1.5 shows a distance of 36 m marked on the scale. It is necessary to draw a scale on a map because as the map shrinks or expands, the scale line also shrinks or expands with it and thus the measure- ments made from the map are not affected. 36m 0 10 20 30 40 50 Scale 1 cm =5m Fig. 1.5 Geographical scale The ratio of the shrunk length to the actual length is known as the shrinkage ratio (S.R.) or the shrinkage factor (S.F.). SF.= shrunk length _ shrunkscale _ shrunk R.F. : measured distance Thus, correct distance = —————— measured area (SRY If a wrong measuring scale is used to measure the length of a line already drawn on a plan or map, the measured length will be erroneous. Then and correct area = R.F. of the wrong scale R.F. of the correct scale correct length = x measured lengthR.F. of wrong scale 2 x 7 R.F. of correct ca | measured area and correct area = [ 1.4 PRINCIPLES OF SURVEYING There are two basic principles of surveying. These find their inherent applications in all the stages of a project, i.e. from initial planning till its comple- tion. 1. To work from whole to part. 2. To locate a point by at least two measurements. 1.4.1 To Work from Whole to Part It is the main principle of surveying and a method violating the principle of working from whole to part should not be adopted until and unless there is no alternative. The main idea of working from whole to part is to localize the errors and prevent their accumulation. On the contrary, if we work from part to whole, the errors accumulate and expand to a greater magnitude in the process of expan- sion of survey, and consequently, the survey becomes uncontrollable at the end. This can be explained by taking a simple example of measuring a horizontal distance AB, say about 120 m with a 20 m chain (Fig. 1.6). The process consists in measuring the distance in parts, as the length of chain is smaller than the distance to be measured and is accomplished by the process of ranging. There can be two alternatives. Fig. 1.6 (a) In the direct method, various points such as C, D, and E are established inde- pendently at a distance of about 20 m each with respect to the two end control points and the distance AB can be measured. As C, D, E, etc. are estab- lished independently with respect to the main control points, error, if any, intro- _ duced in establishing any intermediate point will not be carried in establishing the other points. For example, suppose that point D has been established out of the line AB, as D’ (Fig. 1.6 (a)) and E, F, etc., have been established correctly. ‘The actual distances DC and DE will be in error (D’C and D’E) but all other distances AC, EF, FG, etc. will be correct. Therefore, the error in, this procedure is localized at point D and is not magnified. This method observes the principle of working from whole to part. In the other method, a part, say AC, of the whole distance AB to be measured is fixed by fixing a point C as C’ by judgment or by the process of ranging. Then the other points D, E, F, etc. are fixed with respect to A and C’. Now if point Cis not in line with AB, all the points D, E, F, etc. established will be out of line with an increasing magnitude of error (Fig. 1.6(b)). The length measured will, therefore, be incorrect to a larger extent as compared to the direct method. This method may introduce serious error as the survey at the end becomes uncontrol- lable and hence working from part to whole is never recommended. Fig. 1.6(b) 1.4.2, To Locate a Point by at Least Two Measurements Two control points (any two important features) are selected in the area and the distance between them is measured accurately. The line joining the control points is plotted to the scale on drawing sheet. Now the desired point can be plotted by making two suitable measurements from the given control points. Let A and B be the two control points, whose positions are already known on the plan. The position of C can be plotted by any of the following methods. 1. By measuring distance BC and angle a, as shown in Fig. 1.7(a). 2. By dropping a perpendicular from C on the line AB and measuring either AD and CD or BD and CD, as shown in Fig. 1.7(b). 3. By measuring the distances AC and BC, as shown in Fig. 1.7(c). A B A D B A B al fp NX a c c Cc (@) ) i) Fig. 1.7 1.5 CLASSIFICATION OF SURVEY An attempt has been made here to group the types of survey. However, it is not that significant or satisfactory as there are differences in objectives and dissimi- larities in the procedures employed to distinguish between them. 1.5.1 Based on Accuracy Desired Plane Survey Survey in which the mean surface of earth is regarded as plane surface and not curved as it really is, is known as plane surveying. The follow- ing assumptions are made:(i) A level line is considered a straight line and thus the plumb line at a point is parallel to the plumb line at any other point, (ii) The angle between two such lines that intersect is a plane angle and not a spherical angle. (iii) The meridians through any two points are parallel. When we deal with only a small portion of earth’s surface, the above assump- tions can be justified. The error introduced for a length of an are of 18.5 km is only 0.0152 m greater than the subtended chord and the difference between the sum of the angles of spherical triangle and that of plane triangle is only one second at the earth's mean surface for an area of 195.5 kn*. Therefore, for the limits of the provisions stated above, the survey may be regarded as a plane survey. Plane surveys are done for engineering projects on large scale such as facto- ries, bridges, dams, location and construction of canals, highways, railways, etc., and also for establishing boundaries. Geodetic Survey Survey in which the shape (curvature) of the earth's sur- face is taken into account and a higher degree of precision is exercised in linear and angular measurements is termed as geodetic surveying. Such surveys ex- tend over large areas. A line connecting two points is regarded as an arc. The distance between two points is corrected for the curvature and is then plotted on the plan. The angles between the intersecting lines are spherical angles. All this necessitates elabo- rate field work and considerable mathematical computations. The geodetic surveying deals in fixing widely spaced control points, which may afterwards be used as necessary control points for fixing minor control points for plane survey. This is carried out by the Department of National Sur- vey of India. 1.5.2 Based on Instrument Used Chain Survey Whena plan is to be made fora very small open field, the field work may consist of linear measurements only. All the measurements are done with a chain and tape. However, chain survey is limited in its adaptability be- cause of the obstacles to chain like trees and shrubs. Also, it cannot be resorted to in densely built-up areas. It is recommended for plans involving the develop- ment of buildings, roads, water supply and sewerage schemes. Traverse Survey When the linear measurements are done with chain and tape and the directions or angles are measured with compass or transit respectively, the survey is called traversing. In traversing, speed and accuracy of the field work is enhanced. For example, the boundaries of a field can be measured accu- rately by a frame work of lines along it forming an open traverse. On the other hand, in a densely populated area, the survey work can be carried out with a frame work of lines forming a closed traverse. A traverse survey is very useful for large projects such as reservoirs and dams.Tacheometry This is a method of surveying in which both the h tal and. vertical distances are determined by observing a graduated staff with a transit equipped with a special telescope having stadia wires and anallatic lens. It is very useful when the direct measurements of horizontal distances are inacces- sible. It is usually recommended for making contour plans of building estates, reservoirs, etc. Levelling This is a method of surveying in which the relative vertical heights of the points are determined by employing a level and a graduated staff. In plan- ning a constructional project, irrespective of its extent, i.e. from a small building to a dam, it is essential to know the depth of excavation for the foundations, trenches, fillings, etc. This can be acheived by collecting complete information regarding the relative heights of the ground by levelling. Plane Tabling It is a graphical method of surveying in which field work and plotting are done simultancously. A clinometer is used in conjunction with plane table to plot the contours of the area and for filling in the details. This method of surveying is very advantageous as there is no possibility of omitting any neces- sary measurement, the field being in view while plotting. The details like bound- aries, shore lines, etc. can be plotted exactly to their true shapes, being in view. The only disadvantage of plane tabling is that it cannot be recommended in humid climate. Trlangulation When the area to be surveyed is of considerable extent, trian- gulation is adopted. The entire area is divided into a network of triangles. Any one side of any of the triangles so formed, is selected and is measured precisely. Such a line is called baseline. All the angles in the network are measured with a transit. The lengths of the sides of all the triangles are then computed from the measured length of the baseline and the observed corrected angles with help of sine formula. ab _¢ sinA sinB sinC 1.5.3. Based on Purpose of Survey Engineering Survey Surveys which are done to provide sufficient data for the design of engineering projects such as highways, railways, water supply, sewage disposal, reservoirs, bridges, etc. are known as engineering surveys. It consists of topographic survey of the area, measurement of earth work, provid- ing grade, and making measurements of the completed work till date. These are also known as construction surveys. Defence Survey Surveys have avery important and critical application in the military. They provide strategic information that can decide the course of a war. Aerial and topographical maps of the enemy areas indicating important routes, airports, ordnance factories, missile sites, early warning and other types of radars, anti-aircraft positions and other topographical features can be prepared.Aerial surveys can also provide vital information on location, concentration and movement of troops and armaments. This information may be used for prepar- ‘ing tactical and strategic plans both for defence and attack. Geological Survey In this both surface and sub-surface surveying is re- quired to determine the location, extent and reserves of different minerals and rock types. Different types of geological structures like folds, faults and unconformities may help to locate the possibility of the occurrence of economic minerals, oils, etc. Geographical Survey Surveys conducted to provide sufficient data for the preparation of geographical maps are known as geographical surveys. The maps may be prepared depicting the land use efficiency, sources and intensity of irri- gation, physiographic regions and waterfalls, surface drainage, slope height curve and slope profile and contours as well as the general geology of the area. Mine Survey In this both surface and underground surveys are required. It consists of a topographic survey of mine property and making a surface map, making underground surveys to delineate fully the mine working and construct- ing the underground plans, fixing the positions and directions of tunnels, shafts, drifts, etc., and preparation of a geological map. Archaeological Survey These are done to unearth the relics of antiquity, civilizations, kingdoms, towns, villages, forts, temples, etc. buried due to earth- quakes, landslides or other calamities, and are located, marked and identified. Excavations of the surveyed area lead us to the relics, which reflect the history, culture and development of the era. These provide vital links on understanding the evolution of the present civilization as well as human beings. Route Survey These are undertaken to locate and set out the adopted line on ground for a highway or railway and to obtain all the necessary data. The se- quence of operations in a route survey is as follows: Reconnaissance Survey A visit is made to the site and all the relevant infor- mation is collected. It includes collection of existing maps of the area; tracing the relevant map portion over a paper; incorporating the details of the area, if missing, by conducting rough survey. Preliminary Survey It is the topographical survey of the area in which the project is located. Sometimes an acrial survey is done if the area is extensive. It includes the depiction of the precise locations of all prominent features and fixing the position of the structure on the map. Control Survey It consists in planning a general control system for prelimi- nary survey which may be triangulation or traversing. For location survey, it consists of triangulation. Location Survey It consists in establishing the points, exactly on the ground, for which the computations have been done in the control survey for location.1.5.4 Based on Place of Survey Land Survey It consists of re-running old land lines to determine their lengths and directions, subdividing the land into predetermined shapes and sizes and calculating their areas and setting monuments and locating their positions (monuments are the objects placed to mark the comer points of the landed prop- erty). Topographical, city, and cadastral surveys are some of the examples of land surveying. Topographical Survey This is a survey conducted to obtain data to make a map indicating inequalities of land surface by measuring elevations and to lo- cate the natural and artificial features of the earth, e.g. rivers, woods, hills, etc. Cadastral Survey This is referred to extensive urban and rural surveys made to plot the details such as boundaries of fields, houses and property lines. These are also known as public land surveys. City Survey An extensive survey of the area in and around a city for fixing reference monuments, locating and improving property lines, and determining the configuration and features of the land, is referred to as a city survey. It is similar to the cadastral survey except that refinement observed in making mea- surements is made proportional to the land cost where the survey is being con- ducted, Hydrographic Survey It deals with the survey of water bodies like streams, lakes, coastal waters, and consists in acquiring data to chart the shore lines of water bodies. It also determines the shape of the area underlying the water surface to assess the factors affecting navigation, water supply, subaqueous construction, etc. Underground Survey This is referred to as preparation of underground plans, fixing the positions and directions of tunnels, shafts and drifts, etc. This consists in transferring bearings and coordinates from a surface base line to an underground baseline. An example of this kind of survey is mine surveying. Aerial Survey When the survey is carried out by taking photographs with a camera fitted in an aeroplane, it is called aerial or photogrammetric surveying. It is extremely useful for making large-scale maps of extensive constructional schemes with accuracy. Though expensive, this survey is recommended for the development of projects in places where ground survey will be slow and difficult because of a busy or complicated area. 1.6 REQUISITES OF A GOOD SURVEYOR A good surveyor should have a thorough knowledge of the theory of surveying and skill in its practice. The traits of character and habits of mind are far more potent factors in his success than the technical knowledge. A surveyor should be of sound judgement and reason logically. He should be mild tempered, respectful to his associates, helpful to those working under him and shouldwatch the interest of the employer. Above all, he should not rely upon the results until the accuracy of the work is established by applying suitable checks. By merely reading books about surveying, a surveyor cannot develop skill and judgement and the probability of him performing a satisfactory survey work is quite low. Proficiency can be attained only by the long continued field practice under the supervision of a professional surveyor. 1.7 PRACTICE OF SURVEYING Though the theory of plane surveying seems very simple, its practical application is very complicated. Therefore, the training in surveying should be chiefly directed towards a thorough competency in the field methods, associ- ated instruments and office work. A surveying problem can be tackled by differ- ent methods of observations and by the use of different suitable instruments. A surveyor must be thorough with the advantages and disadvantages of the different methods of observations and also to the limitations of the instruments. Normally the time and funds are limited. A surveyor’s competency, therefore, lies in selecting methods which yield sufficient accuracy to serve the purpose. 1.8 SURVEYING—CHARACTER OF WORK The work of the surveyor which mainly consists of making measurements can be divided into two parts—field work and office work. 1.8.1 Fleld Work For a true representation of the field conditions so as to plot the plans and sections with ‘desired accuracy, sufficient data should be obtained from field work. It consists of adjusting instruments and taking due care of these, making surveying measurements, and recording the measurements in the field note book in a systematic manner. Adjustments and Care of Instruments The adjustment of a surveying in- strument means the bringing of fixed parts of the instrument into_proper relation with one another. For this, a surveyor should understand the principles on which adjustments are based, the process by which a faulty adjustment is discovered, the effect of the adjustment on the instrument and the order of the adjustments. Keeping the instruments in adjustment is logical for accurate field work. This necessitates that some parts of the surveying instruments should be adjustable. A proper care of the instrument keeps it in a fit condition for its usage. Following are a few suggestions to be kept in mind while using the surveying instruments. (1) The chain should be checked for its links, rings, and length before its use. All the knots and kinks should be removed by giving gentle jerks while laying it on the field.Steaks eC eke is (2) Tape should be kept straight when in use. (3) The staff and rod should be either placed upright or supported for the entire length when in use. (4) The instrument should be removed from and placed gently in the box. (5) The instrument should be protected from vibration and impact. (6) The tripod legs should not be set too close together and should be planted firmly on the ground. (7) During observation, the surveyor should see to it that the tripod is not disturbed. : (8) The various clamping and adjusting screws should not be tightened far more than necessary. (9) The objective and eye piece lens should not be touched with fingers. (10) The dirt and dust should regularly be cleaned from the movable parts of the instrument. (11) When the magnetic needle of the instrument is not in use, it should be raised off the pivot. Surveying Measurements The surveying measurements consists in measuring horizontal and vertical distances, horizontal and vertical angles, horizontal and vertical positions and directions. The distance between two points measured horizontally throughout is called the horizontal distance. If a distance is measured on a slope, it is immediately reduced to the horizontal equivalent by applying suitable corrections. Such a measurement is made with a chain, tape, or by an optical or electronic instrument. The distance measured in the direction of gravity is called vertical distance and is equivalent to the difference in height. This measurement is done with an instrument known as level along with a leveling staff. An angle measured in a horizontal plane at the points of measurement is called a horizontal angle and an angle measured in a plane that is vertical at the point of observation, and contains the points, is called a vertical angle. Vertical angles are measured upwards or downwards from the horizontal plane. Angles measured upwards are called plus angles or angles of elevation and those measured downwards are called minus angles or angles of depression. Both the horizontal and vertical angles are measured with an instrument known as transit. The directions of the courses are expressed as bearings. A bearing is a clockwise horizontal angle from a reference direction, usually north. This is measured with an instrument known as compass. The relative horizontal position of various points are determined by traverse or by triangulation. A traverse consists of the measurement of a series of horizontal courses (lengths) and thé horizontal angles between the courses or the directions of the courses. Triangulation consists of the measurement of the angles of a series of connected triangles and its direction. Both in traversing and triangulation, the final results are computed by trigonometry and are best ex- pressed by rectangular coordinates.The relative position of the points are determined by a series of level obser- vations with the line of sight being horizontal. The results of leveling are re- ferred to a standard datum, normally mean sea level. The vertical heights above the datum are called elevations. The methods of measurements will be dealt one by one in the subsequent chapters to follow. Recording Field Notes Field notes are the written records of the field work made at the time the work is done. Records copied from field notes or data recorded afterwards from memory, may be useful, but are not regarded as field notes. A surveyor should keep in mind not only the immediate use of the data, but also those which may be expected to arise in future. Therefore, the field notes must be complete and accurate as far as possible. The importance, accuracy, legibility, integrity, arrangement and clarity that the field notes should have must be over emphasized. Accuracy All the measurements should be accurate, depending upon the precision desired. Legibility It should always be kept clearly in mind that the notes may be utilized by someone else who has never even visited the site of the survey. Therefore, all the notes should be legible and contain a professional touch. Integrity The notes should be complete in all respects before leaving the site of the survey. Even a singie omitted measurement may pose a serious problem while computing or plotting in the office. Arrangement It should be made clear as to how the work began and ended. The note forms should be appropriate to the particular survey and should be arranged in the sequence of the work done in field. Clarity Sketches and tabulation of field data should be clear and readable. It should be remembered that the notes may be used by someone else in future. Ambiguous notés lead to mistakes in drafting and computation. Field Book Field notes are usually recorded on standard ruling sheets in a loose-leaf or bound field book. The format of the standard ruled sheet depends upon the type of the instrument used for surveying and is touched upon in detail, in appendices I to IX. However, some general suggestions are presented below. 1. Use a notebook that may stand hard usage. 2. Achard lead pencil, 3H, should be used to record field notes. The reason is that by using a hard pencil, indentations are made on the paper and later, if due to any reason the notes are smeared, the data can still be ascertained by examining the indentations. 3. Erasure should never be made in the field book. If a measured value is recorded incorrectly, it should Le cut by a horizontal line and the correct value should be recorded above the cut value. 4. The notes should read from left to right, and from the bottom io top as in the working drawings.5. The left page of the field book is used for recording data, while the right page is used for sketches. 6. All the calculations and reductions made in the ficld should be indicated on additional sheets and may be cross-referenced as and when required. 7. On the top of the field notes, names of the survey party, instrument used, data, weather, etc. should be mentioned. This is particularly useful when the field notes are presented as evidence in court. 8. Atthe end of the day’s work, the notes should be signed by the notekeeper. In recording notes in the field book, a beginner is usually confused whether to book it from the bottom to the top of the page or from top to down. Usually, in making sketch of the course being surveyed, the field book is held with its top towards the next station and if the field notes are recorded on opposite page, it will be convenient to note and read from the bottom up so as to correspond with the sketch. The examples are survey of railways and highways courses. Whereas, when complete sketch is made on one page, such as for a closed traverse, it may be more convenient to tabulate the corresponding notes on the opposite page to read from the top down. 1.8.2 Office Work Itconsists of making the necessary calculations or computations for transforming the field measurements into a form suitable for plotting. Knowledge of geometry and plane trigonometry; determining locations, plotting the measurements and drawing a plan or map, inking-in and furnishing the drawings, and calculating areas and volume, all involve office work. This topic is dealt within detail in the subsequent chapters depending upon the type and method of surveying used for a particular work. Inking-in and furnishing the drawings is described here as it will be a general feature for all types of survey. Inking-In-Drawings Either inks or water colours may be N used. Following are some of the standard colours usually recommended for topographic maps to represent the features. Black—Lettering and all construction works, e.g. houses, toads, rails, culverts, bridges, etc. Burnt sienna—Alll land forms, e.g. streams, lakes, ponds, marshes, etc. Green—Plantations, e.g. trees, growing crops, grass, etc. Fumishing Drawings The drawings should be furnished with meridian arrows (Fig. 1.8) of sufficient length, cross- sections, lettering of sufficient size arranged neatly to give a pleasant and artistic look, eye catching titles and symbols. The symbols or conventional signs need a special elabora- tion as these are used to represent the objects on map. The Fig. 1.8 Meridian arrowssize of the symbol should be in proportion with the scale of the map. Some of the symbols are shown in Fig. 1.9. Object Symbol Colour Single Track SEEEEEEEEEEEE Black Double Track H Black Pucca Road Vermilion Red Kutcha Road Vermilion Red Footpath Vermilion Red Fencing Post and Rail Vermilion Red Fence Tunnel (Road or Rail Black Road) Canals and Ditches Black “Aqueducts and Water Black Pipes Dam Black Bridge Black Stream Prussian Blue Pond Prussian Blue Falls and Rapids Black Road in Embankment Road in Cutting Indian Blue Ink. and Road in Vermilion Red Indian Blue Ink and Road in Vermilion Red Fig. 1.9(a) Conventional symbolsIndian Black Ink BDVor Boundary Chain Garden oo Dotted and Qo a Hopper's Green Wash Indian Black Ink ii dhib Boundary Chain. Marshy Ground br ‘tat alin Dotted and Hooper's Green Wash Indian Black Ink ere Boundary Chain Jungle reed Dotted and Hooper's Green Wash Cultivated Land Green eVvos ‘Orchard ea oa co Fenceotanykind(or = -------------- Black Board Fence) Barbed Wire Fence SH Black Smooth Wire Fence: o-oo Black Rail Fence Wrnrwv Black Hedge Fence Qocemcmncanace Green Stone Fence PEcoscocrsae Black TelegraphorTelephone TTT TTT Black Line Powerline wnven ee nee eee Black Wall ————— Vermilion Red Gate on & Vermilion Red Fig. 1.9(b) Conventional symbolsWail and Gate —aao— Vermilion Red Building (Large Scale) Black Building (Kutcha) Umber Huts Yellow Temple : Grimson lake ‘Church ; Crimson lake Mosque Crimson lake BOM Benchmark Bi LJ ack Openwell Purssina blue Tubewell Tp Black Footpath ~ Black Metalled road Bumt sienna Unmetatied road Bumtsienna Fig. 1.9(¢) Conventional symbols 1.9 ERRORS It is understood that every measurement contains errors of unknown magnitude due to several reasons and hence no measurement in surveying is exact. A sur- veyor should, therefore, understand thoroughly the nature of the sources and behaviour of the errors which may affect the results. A knowledge of the errors and procedures necessary to maintain a required precision aid the surveyor to develop a good judgement in his work. A true error may be defined as the difference between a measurement and its true value. As the true value of a measurement is never known, the exact error present is therefore never known, and is thus always unknown.LeSK 3 oats 1.9.1 Sources of Error The sources of error in surveying may be classified as natural, instrumental, and personal. Natural Errors These result from the temperature, refraction, obstacles to measurements, magnetic declination, etc. For example, the length of a steel tape varies with changes in temperature. Such sources of error are beyond the control of the surveyor, but by taking precautionary measures and adopting suitable methods to fit into the conditions, the errors can be contained within permissible limits, Instrumental Errors These result from the imperfect construction and adjustment of the instrument, The incorrect graduations of a steel tape and the improper adjustment of the plate levels of a transit are a few examples. The effects of most of the instrumental errors can be brought within the desired limits of precision by applying proper corrections and selecting suitable field methods. Personal Errors These arise from the limitations of the human senses such as sight, touch, and hearing. For example, improper bisecting of the object by fixing the line of sight of a transit while measuring angles is a personal error. 1.9.2 Types of Errors Errors in a measurement may be positive or negative. The former occurs if the measurement is too large and the latter if too small. Errors are classified as systematic errors and accidental errors. Systematic Errors These are the errors which occur from well-understood causes and can be reduced by adopting suitable methods. For example, the error due to sag of a tape supported at ends can be calculated and subtracted from each measurement. However, the tape can be supported throughout its length at short intervals and the sag error may be reduced to a negligible quantity. It always has the same magnitude and sign so long as the conditions remain same and such an error is called constant systematic error. Whereas, if the conditions cliange, the magnitude of the error changes and this is known as variable systematic error. A systematic error follows a definite mathematical or physical law and, therefore, a correction can always be determined and applied. It is also known as cumulative error, Accidental Errors These are the errors due to a combination of causes and are beyond the control of surveyor. It can be plus or minus. Calibration of a chain is an example of an accidental error. 1.10 DISTINCTION BETWEEN MISTAKE AND ERROR Mistakes are caused by the misunderstanding of the problem, carelessness or poor judgement. These can be corrected only if discovered. The best way is to compare several measurements of the same quantity and do away with the oddpoesia ees Westies Seas ee SR one sere measurement which does not follow any law. In surveying, attempts are always made to detect and eliminate mistakes in field work and computations. The de- gree to which a surveyor is able to do this is the measure of reliability. On the other hand, error is defined as the difference of the measured and true value of the quantity. The distinction arises from the fact that mistakes can be avoided by being careful, whereas errors result from sources which can be minimized but not avoided. 1.11 DISTINCTION BETWEEN PRECISION AND ACCURACY Both precision and accuracy are used to describe physical measurements. The manufacturers, while quoting specifications for their equipments, and surveyors and engineers, to describe results obtained from field work, make use of these ‘terms frequently. Precision is referred to as the degree of fineness and care with which any physical measurement is made, whereas accuracy is the degree of perfection obtained. It follows that a measurement may be accurate without being precise and vice versa. Accuracy is considered to be an overall estimate of the errors, including systematic errors present in measurements. For a set of measurements to be considered accurate, the most probable value or sample mean must have a value close to the true value as shown in Fig. 1.10(a). Precision represents the repeatability of a measurement and is concerned with only random errors. A set of observations that are closely grouped together and have small deviations from the sample mean will have a small standard (probable) error and are said to be precise. It is quite possible for a set of results to be precise but inaccurate as shown in Fig. 1.10(b), where the difference between the true value and the mean value is caused by one or more systematic errors. Since accuracy and precision are the same if all systematic errors are removed, precision is sometimes referred to as internal accuracy. Ax) Ax) ‘Mean value Mean — value Systematic error ' ' Precise and Precise but accurate results inaccurate results x Te x Pet hye value True value (a) (b) Fig. 1.10 Precision and accuracyThe ratio of precision of a measurement to the measurement itself is termed as relative precision and is expressed as | in d/s,, where d is the measurement and s, is the standard error. For electromagnetic distance measurement (EDM) instruments and total stations, the relative precision is expressed in parts per million (ppm). The relative precision is normally specified before starting a survey so that proper equipment and methods can be selected to achieve the desired relative precision. 1.12 PLANIMETRIC MAP AND HYPSOMETRIC MAP. Planimetric map or line map shows the natural or cultural features in plan only. ‘Whereas, a hypsometric map presents relief by conventions such as contours, hachures, shading, tinting, etc. 1.13 PENTAGRAPH It is an instrument used for enlarging, reducing or reproducing the plans. 1.13.1 Construction It consists of four tubular brass arms square in section. Two of these are long (AB and AC) and are pivoted at one end A (Fig. 1.11). The other two (DE and DF) are short and are hinged together at end D, and are connected to long arms at E and F, having equal sides in all the positions of the instrument. A weight W, known as fulcrum, is attached to long arm AB to fix the frame in a desired position and the instrument moves about this. The instrument is fixed on small rollers to allow free movement on the plan. A E c Fig..1.11 Pentagraph Arms AB and DF are provided with graduations 1/2, 1/3, 1/4, etc. to give a corresponding enlargement or reduction. Arm AB carries a standing tubularframe with an index line and a vertical axis of rotation which slides on the arm. The arm DF also carries a frame with an index line and a sliding pencil. Both these frames can be clamped at any division with the respective clamping screw. In Fig. 1.11 points C and G are the tracing point and pencil point, respectively. The instrument in this position is used for reduction. These two points are interchangeable. When G is used as tracing point and C as pencil point, the instrument can be used for enlargement. The arm AC, carrying a tracing point at C, when moved over the boundary of the plan with the pencil fixed at G, produces the desired reduced scale copy. The instrument is very suitable for reductions but for enlargements the results are not satisfactory. 1.13.2 Principle The working of the pentagraph is based on the principle of similar triangles. Let AB and AC be two straight arms hinged at A. E and F are two points on the respective arms equidistant from A (Fig. 1.12). AFDE is a parallelogram. Let AC be hinged at J and the end B moved. The movement of points G and J will be in the ratio of their distances from F and E, respectively. Fig. 1.12 ADEF is a parallelogram. Hence, FG is parallel to AE. Also ZGFB = ZBAC WGF and WJA are similar triangles. WG _ FW WI AW Any displacement of J will give a corresponding displacement of G through FW/AW and hence the plan placed at J will be reduced. Hence,Fig. 1.13 Eidograph 1.14 EIDOGRAPH The eidograph is also used for the same purposes as the pentagraph. The pentagraph requires four supports on the paper and has numerous joints; its action is apt to be unsteady. In contrast, eidograph has only one support upon which the entire instrument moves steadily and regularly. All the joints of theeidograph consist of fulcrums fitting in accurately ground bearings, the motion around these fulcrums being capable of adjustment for regularity as well as ac- curacy. Further, an eidograph may be set to form a reduced copy bearing any required proportion to the original, while a pentagraph can be set for only few proportions specifically marked on it. 1.14.1 Construction Figure 1.13 shows the constructional details of an eidograph. The heavy weight (H) of the eidograph is formed by lead with brass covering. It has three or four needle-points to keep it steady on the paper. The pin, forming the fulcrum upon which the whole instrument moves, projects from the centre of this weight on its ‘upper side, and fits into a socket attached to sliding box (K). The centre beam (C) fits into and slides through the box, and can be adjusted to any desired position with respect to the fulcrum. It can be fixed by a clamping screw attached to the box. The centre pins of the pulley-wheels (J) are fitted into the deep sockets attached to each end of the centre beam, The pulley wheels have two steel bands (I) attached to their circumference, so that they can move only simultaneously, and to exactly the same amount. By means of screw adjust- ments these bands can have their lengths regulated so as to bring the arms of the instrument into exact parallelism and, at the same time, to bring them to such a degree of tension so as to provide the motions of the arms with the required steadiness, which forms one of the advantages of the instrument over the pentagraph. The arms, A and B, of the instrument pass through sliding boxes upon the under side of the pulley-wheels; these boxes, like that for the centre beam, being fitted with clamping-screws, by which the arms can be fixed in any desired position. At the end of one of the arms is fixed a socket with clamping- screw, to carry a tracing-point, G, and at the end of the other is a socket for a loaded pencil, D, which may be raised when required by a lever, FF, attached to a cord which passes over the centre of the instrument to the tracing-point. The centre beam, C, and the arms, A and B, are made of square brass tubes, divided exactly alike into 200 equal parts, and figured so as to read 100 each way from their centres. The boxes through which they slide have verniers, by means of which these divisions may be subdivided into 10, so that with their help, the arms and beam may be set to any reading containing not more than three places of figures. A loose leaden weight is supplied with the instrument to fit on any part of the centre beam, and keep it in even balance when set with unequal lengths of the centre beam on each side of the fulcrum. 1.14.2 Principle The pulleys being of exactly equal size, when the steel bands are adjusted so as to bring the arms of the instrument into exact parallelism, they will remain par- allel throughout all the movements of the pulleys in their sockets, and thus will always make equal angles with the centre beam. If, then, the two arms and the centre beam are all set so that the readings of their divisions are the same, aline drawn from the end of one arm across the fulcrum to the end of the other arm will form, with the beam and arms, two triangles having their sides about equal angles proportionals, and being, therefore, similar. Hence any motion ‘communicated to the end of one arm will produce a similar motion at the end of ‘the other, so that the tracing-point being moved over any figure whatever, an exactly similar figure will be described by the pencil. Suppose it is required to set the instrument so that the proportion of the copy to the original be a : b. Let x be the reading to which the instrument should be set, then the centre beam and arms are each divided at their fulcrums into portions whose lengths are 100 — x and 100 + x, respectively consequently, (100 — x)(100 + x) = a/b => x= 100(b-a)b + a) Thus, if the proportions are 1: 2, we have x = 100 (2- 1)(2 + 1) = 33.3 The instrument must be set with the third divisions of the verniers beyond the indices and the third divisions of the instrument beyond the 33rd. The readings to which the instrument must be set for given proportions is given in Table 1.1. Table 1.1 Proportions ; 1:4 0:5 1:6 2:3 2:5 3:4 3:5 Readings 333 50 60 66.7 71420429 14.325 When the copy is to be reduced, the centre beam is to be set to the reading found, as above, on the side of the zero next to the arm carrying the pencil-point, and this arm is also to be set to the same reading on the side of its centre or zero nearest to the pencil-end, while the tracer-arm is to be set with the reading farthest from the tracer. When the copy is to be enlarged, these arrangements thust of course be reversed. Figure 1.14 represents the setting which makes the linear dimensions get re- duced to one-fourth (Fig. 1.14(a)) and get enlarged to four times (Fig. 1.14(b)). For proportion 1 : 4, the reading to be set is 60. P represents the position of the pencil point, T that of the tracer, and F the place of the fulcrum, P P (a) Reduction (b) Enlargement Fig. 1.14 Reducing/enlarging drawings (1 : 4)1.15 UNITS OF MEASURE The system of units used in India in the recent years is M.K.S. and S.I. But all the records available in surveying done in the past are in F.P.S. units. Therefore, for a professional it becomes necessary to know the conversion of units from one system to another, a few of which are listed below and many more can be computed, 1 ft 0.3048 m 1 mile 1 yard 1 mile -609 km 1 sq mile 590 km? 1 sq mile = 640 acres 1 acre 3,560 sq ft 1 hectare ATL acres Exercises 1.1 Define and differentiate the following: G@) Plan and map Gi) Error and mistake (iii) Accuracy and precision (iv) Plane and Geodetic surveys 1.2 Convert the following representative fractions into scales. (i) 1/100,000 (ii) 1/1,000,000 (ii) 1/20,000 [Ans. 1 cm =1km, 1 em = 10 km, 1 cm = 0.20 km] 1.3 A rectangular piece of property has sides measuring 300 m and 200 m. What is the area of the property in square metres, square kilometres, acres, hectares? [Ans. 6 x 10°, 6 x 10°, 4.820, 6.0] 1.4 What information should be included in a good set of field notes? 1.5 Briefly discuss the requirements of good field notes. 1.6 Briefly discuss the following: i) Earth’s surface (ii) Level surface (iii) Great circle (iv) Plumb line 1.7 Define surveying. What are the principles of surveying? Explain them briefly. 1.8 Write short notes on the following: (i) Geodetic survey (ii) Defence survey (iii) Mine survey (iv) Cadastral survey (v) Aerial survey 1,9 Draw symbols for the following: @) Cemetery (ii) Mosque (iii) Barbed wire (iv) Triangulation station (v) Culvert1.10 LAL 1.12 14 15 Discuss briefly the different types and sources of errors in surveying. Explain the principle and working of pentagraph with the help of neat sketches. Explain the construction and principle of working of eidograph. Objective-type Questions Surveying is the art of determining the relative positions of points on, above or beneath the surface of the earth, with respect to each other, by the measurement of (i) distances (ii) directions (iii) elevations (a) G), (ii), (iii) are required (b) only (i) is required (c) only (ii) required (d) only (iii) is required The main principle of surveying is to work from (a) higher level to the lower level (b) lower level to the higher level (c) part to whole (d) whole to part The error which occurs while conducting the survey from whole to part and part to whole is (a) same (b) in whole to part, it is localized and in part to whole it is expanded (c) in whole to part it is expanded and in part to whole it is localized (d) in both the methods error is localized A point R can be located by the two control points P and Q by (i) measuring PR and QR from P and Q, measure distance of R and plot (ii) dropping a perpendicular from R on PQ, meeting the line in S, mea- sure PS, SQ and plot (iii) distance QR and angle @ between QR and QP (a) only (i) is correct (b) by (i) and (ii) both (c)_by (i), Gi) and (iii) (d) by none of them The objective of a survey is to (i) prepare a plan or map (ii) determine the relative position of points (iii) determine position of points in a horizontal plane (iv) determine position of points in a vertical plane (a) only (i) is correct (b) only (i) and (ii) are correct (c) (i), (ii), (iii), (iv) all are correct (d) none of them are correct16 17 1.8 19 1.14 1.15 1.16 The difference in the length of an arc and its subtended chord on earth’s surface for a distance of 18.5 km is about (a) 0.1cm (b) 1.0cm (c) 10cm (d) 100 cm Surveys which are carried out to provide a national grid of control for preparation of accurate maps of large areas are known as (a) Plane surveys (b) Geodetic surveys (c) Geographical surveys (d) Topographical surveys Surveys which are carried out to depict mountains, water bodies, woods and other details are known as (a) Cadastral surveys (b) City surveys (c) Topographical surveys (d) Hydrographic surveys Hydrographic surveys deal with the mapping of (a) heavenly bodies (b) hills (c) large water bodies (d) canal system Plan is a graphical representation of the features on large scale as pro- jected ona (a) horizontal plane (b) vertical plane (c) in any plane (d) none of the above Map is a graphical representation of the features on small scale as pro- jected ona (a) horizontal surface (b) vertical surface (c) in any surface (d) none of the above The survey in which the curvature of the earth is taken into account is called (a) Geodetic survey (b) Plane survey (c) Preliminary survey (d) Hydrographic survey The effect of the curvature of the earth’s surface is taken into account only if the extent of survey is more than (@) 100 km? (b) 260 km? (c) 195.5 km? (a) 300 km? Plane survey is conducted for the area up to (@) 260 km’ (b) 100 km? (c) 195.5 km? (d)_ 160 km? The difference between the sum of the angles of a spherical triangle on the earth’s surface to that of the angles of the corresponding plane tri- angle is only one second for every (a) 260 km’ (b) 160 km? (c) 360 km? (qd) 195.5 km? The following are the subdivisions of engineering survey. Match them. (I) Reconnaissance survey (A) To determine feasibility and rough cost of the scheme. (Il) Preliminary survey (B) To collect more precise data, to choose the best location for the work and to estimate the exact quantities and costs.(III) Location survey (C) For setting out the work on the ground. (a) -A, II-B, TI-C (b) I-B, I-A, II-C (c) -C, I-A, II-B (d) IB, I-C, III-A 1.17 Match the following: (1) Topographical survey (A) To determine the natural features of a country such as hills, valleys, rivers, nuallas, lakes, woods, etc. (II) Cadastral survey (B) To survey for the features such as roads, railways, canals, buildings, towns, villages, ete. (I) City survey (C) To locate the boundaries of fields, houses, etc. To determine quantities and for collection of data for road, railways, reservoirs, sewerage, water supply scheme, etc. (E) For laying out plots and construction streets, water supply systems and sewers. (IV) Engincering survey (D (a) LA and B, II-C, II-E, IV-D (b) I-C, II-A and B, III-C, IV-E (c) I-D, I-A and B, III-C, IV-E (d) I-B, II-C, III-A, IV-D and E Systematic errors are those errors (a) which cannot be recognized (b) whose character in not understood (c) whose effect are cumulative and can be eliminated by adopting suit- able methods (d) which change rapidly Theory of probability is applied to (a) accidental errors only (b) cumulative errors only (c) both accidental and cumulative (d) none of the above 1.20 The error due to bad ranging is 1.2. (a) cumulative (+ve) (b) cumulative (—ve) (c) compensating (d) cumulative (+ve or -ve) The difference between the most probable value of a quantity and its ob- served value is (a) true error (b) weighted observation (c) conditional error (d) residual error1.22 Which of the following scales is the largest one (a) lcm=50m (c) RF = 1/300 000 (b) 1:42 000 (@) 1em=50km 1,23. Mistakes are errors which arise from i) lack of attention ii) poor judgment (a) only (i) is correct (b) (i), (ii) are correct (ii) carelessness (iv) confusion (c) (i), (ii), (iii), (iv) all are correct (d) none of them is correct 1.24 Errors are of same size and sign of mistakes, if it follows some definite (i) mathematical law (a) (i) and (ii) are correct (c) only (ii) is correct (ii) physical law (b) only (i) is correct (d) none is correct 1,25. The shrinkage factor of an old map is 24/25 and the RF is 1/2400, then the corrected scale for the map is (a) 1/2400 (b) 1/2500 (c) 1/600 (d) 1/60 000 1.26 The RF of scale 1 cm = 1 km is (a) 1/100 000 (b) 1/1000 (c) 1/100 (d) 1/10 1.27 The degree of precision required in survey work mainly depends upon the (a) purpose of survey (c) sources of error 1.28 Match the following: Type of map (D) Geographical map (I) Topographical map (II) Location map (IV) Forest map (V) Cadastral map (b) area to be survey2d (d) nature of the field Scale (A) lem= 160km (B) lem=2.5km (C) 1: 2500 to 1 : 500 (D) 1: 2500 (E) 1: 1000 to 1: 5000 (a) I-A, I-B, II-C, IV-D, V-E (b) I-B, I-A, III-C, IV-D, V-E (c) I-C, I-D, I-E, IV-A, V-B (d) I-E, U-B, III-D, IV-B, V-A 1,29 It is convenient to record the field notes for a closed traverse in the field book (a) from left to right (c) from top to down (b) from right to left (d) from bottom to top 1.30 The smallest length that can be drawn on a map is (a) 0.2mm (c) 10mm (b) 0.5mm (d) 15mm 1.31 Which of the following instrument(s) is (are) used for enlarging or reduc- ing the drawings(i) pentagraph (a) (i) only (c) both (i) and (ii) (a) 50 (b) 60 (ii) eidograph (b) (ii) only (d) none of the above 1.32 Suppose a drawing is to be reduced by a proportion 4 : 5, the reading to which the instrument should be set will be (© 143 Arar aea List IT 1.34 A hut can be shown by the symbol List I (Object) (a) Hedge (b) Wire fencing (c) Pipe fencing (d) Wood fencing Codes (a) A B 1 2: (b) A B 4 2 (c) A B 1 2 (d) A B (a) ‘ae @i 1.35 (a) Temple (c) Church The symbol represents (b) Mosque (d) Hut (@ 1 1.33 Match List I with List II and select the correct answer using the codes given below the lists: —— Answers to Objective-type Questions 1.1 (a) 1.6 (b) 111 (a) 1.16 (a) 1.21 (d) 1.26 (a) 1.31 © 1.2 17 1,12 1.17 1.22 1.27 1.32 (d) (b) (a) (a) (a) (a) (d) 1.3 (b) 18 () 1.13 (¢) 1.18 (c) 1.23 (¢) 1.28 (a) 1.33 (a) 1.4 ©) 1.9 (c) 1.14 (c) 1.19 (a) 1.24 (a) 1,29 (c) 1.34 (d) 1.5 (c) 1.10 (a) Ls @ 1,20 (a) 1.25 (b) 1.30 (a) 1.35 (c)Horizontal Measurements 2.1 INTRODUCTION History reveals that the measurement of horizontal distance has taken a variety of forms with marked variations in the accuracies achieved. Various methods such as rope stretching, bamboo, pacing, chaining, optical (tacheometry) and electro- magnetic distance measurement exist, varying from the crude to the highly sophisticated ones. The cost of making a measurement increases with the desired precision of the work. Therefore, it is important to know the methods available and their accuracies so as to obtain the required precision with economy. Measurement of horizontal distance is probably the most basic operation per- formed in surveying and perhaps the most difficult as well. The horizontal dis- tance between two points is the distance between the plumb lines through the points. It is important to emphasize that in plane surveying, the distances mea- sured should be horizontal. When distances are measured on slopes, sufficient data should be collected so as to compute horizontal projections. Rope stretching and bamboo measurements are very crude methods and are obsolete, Pacing can be recommended if an error of 5% is permissible and if the ground is flat. In the optical methods, principles of optics are used. The distances are not actually measured in field but are computed indirectly by using the principles of optics. The instrument used for making observations is called tacheometer. Tacheometry may be employed when the ground is rough, undulating and not suitable for chaining. The electromagnetic distance measurements can be made by using light waves. or radio waves. The instruments used in the former case are called Geodimeter and Makometer, whereas distomat uses radio waves. Electronic methods and aerial photogrammetry yield results with high preci- sion but are expensive.The most common method of measuring the distances is by the use of chain and tape. This operation is called chaining irrespective of whether a chain or a tape is used, Chaining is recommended for moderately small areas and measurement of ill-defined details, e.g, edge of a marsh or for filling in details between already established control points. Chain is used to measure the lengths of the line and tape is employed to measure the perpendicular distances to the chain line, called offsets. In ‘the process of chaining, the survey party consists of a leader (the surveyor atthe forward end of the chain), a follower (the surveyor at the rear end of the chain)-and an‘assistant to establish intermediate points. The accuracy to which measurements can be made with chain and tape varies with the methods used and the precautions exercised. The precision of chaining for ordinary work ranges from 1/1000 to 1/30 000 and precise measurements such as baseline may be of the order of 1 000 000. Good chaining and standardized and adjusted chain in good order may be expected to give an accuracy of 1/500 to 1/1 000 000. Accuracy in the base measurement seldom exceeds 1/500 000. The scope of the chapter limits the study of various methods of horizontal measurements to that of chain and tape. 2.2 CHAIN SURVEYING Itis the branch of surveying in which the distances are measured with a chain and tape and the operation is called chaining. All the distances measured should be ‘horizontal. However, if measured on slopes, the measurements are to be subse- quently reduced to horizontal equivalents. To have a better understanding of chain surveying, a few terms need explanation. Here reference may be made to Fig. 2.1.Main Station Main station is a point in chain survey where the two sides of a traverse or triangle meet. These stations command the boundaries of the survey and are designated by capital letters such as A, B, C, etc. Tie Station or Subsidiary Station Tie station is a station on a survey line joining two main stations. These are helpful in locating the interior details of the area to be surveyed and are designated by small letters such as a, b, c, etc. Main Survey Line The chain line joining two main survey stations is called main survey line. AB and BC are examples of main survey lines. Tie Line or Subsidiary Line A chain line joining two tie stations is called tie line such as ab or cd. It is also called auxiliary line. These are provided to locate the interior details which are far away from the main lines. Base Line It is the longest main survey line ona fairly level ground and passing through the centre of the area. It is the most important line as the direction of all other survey lines are fixed with respect to this line. Check Line Check line or proof line is a line which is provided to check the accuracy of the field work. The measured length of the check line and the com- puted one (scaled off the plan) must be the same, AD is an example of check line, Offset It is the distance of the object from the survey line. It may be perpen- dicular or oblique. Chainage Itis the distance of a well-defined point from the starting point. In chain surveying it is normally referred to as the distance of the foot of the offset from the starting point on the chain line. The operation of measuring the distance is termed as chaining/taping. Field Work in Chain Survey Suppose a plan is required for a small area as shown in Fig, 2.1. The surveyor should first of all thoroughly examine the ground to ascertain as to how the work. can be arranged in the best possible manner. This is known as reconnaissance. In this process, the surveyor selects suitable ground points to be used as stations like A, B, or C, etc. Stations are arranged so that the entire area may be controlled from these and all the main survey lines, e.g. AB, BC, CD, etc. run near to the boundaries. The survey lines should not be many and lie over flat level ground as far as possible. The triangles formed by survey lines should be well conditioned. The main survey lines are measured with a chain and offsets are taken to the crooked boundaries. offsets are taken wherever there is a bend or any special feature in the boundary. In the case where the boundary forms a smooth curve, offsets are taken at the end of each chain. Offsets should be short particularly for locating important details,The lengths and positions of offsets being known, the boundaries can be plot- ted to their shapes. The other details, which are deep inside the area such as a pond or well as shown in Fig. 2.1, can be located by selecting tie stations, draw- ing tic lines and taking offsets to the ground features. The equipments and acces- sories required for chaining are described in the following sections. 2.3 CHAIN Gunter, revenue, engineer and metric chain are the various types of chains which are normally used for surveying. The chains are mostly divided into 100 links. While Gunter’ s chain is 66 ft long (100 links), the revenue chain is 33 ft long (16 links) and the engineer’s chain is 100 ft long (100 links). Metric chains are either 30 m (150 links) or 20 m (100 links) in length. The constructional detail of metric chain are presented in details as it is generally used for the routine measurement of distances. Metric Survey Chain (20 m or 30 m) A metric chain (Fig. 2.2) divided into 100 links is made of galvanised mild steel wire 4 mm in diameter. The ends of each link are bent into loops and connected together by means of three oval rings, which afford flexibility, to the chain. The length of the link is the distance between the centres of the two consecutive middle rings. The ends of the chain are provided with brass handles with swivel joint, so that the chain can be turned round without twisting. The outside of the handle is the zero point or the end point of chain. The length of the chain is measured from outer end of the handles. Metallic tags are used at 5, 10, 15, 20, 25 m (Fig. 2.3) intervals for quick reading. The metallic tags used are called tallies. Small brass rings (Fig. 2.3(a)) are provided at every metric length except at 5, 10, 15, 20 m, etc. The handles of the chain are provided with grooves so that the arrows can be held at the correct positions. 13-13 Hi 42th 93,2121 13 461,21 —> - 58> 7 49 Small link 44 Large link Ring 8 SWG (4 mm) 75 So-—EE Eye bolt \ Hol z + eet Connecting ring of 44 Hole 38 Coller SWG oval shape + 6¢ \— Handle Engraved 20 or 30 m on surface to indicate the length of chain Fig. 2.2. Details of metric chain“0 0 0 Brass ring at every Tally at 5m Tally at 10 m Tally at 15 m metre length length length length Fig. 2.3 Ring and tallies of a chain Suitability of Chain 1. It is suitable for rough use only. 2. It can be easily repaired in field. 3. It can be read easily. Unsuitability of Chain 1. Being heavier, it sags considerably when suspended in air. 2. Its length alters by shortening/lengthening of links. Therefore, itis suitable for ordinary work only. Unfolding the Chain (undoing the chain) The leather strap is removed and with both the handles of the chain in the left hand the chain is thrown well forward with the right hand. The leader then takes one of the handles of the chain and moves forward until the chain is extended to full length. The chain is checked and kinks of bent links are removed. Folding the Chain (doing the chain) The chain is pulled from the middle and the two halves of the chain are so placed as to lie alongside each other. Commencing from the middle, two pairs of links are taken at a time with the right hand and are placed obliquely across the others in the left hand. The chain is then folded into a bundle and fastened with a leather strap. Testing of Chain During its use, the links of a chain get bent and the length is shortened. On the other hand, the length of a chain may increase by stretching of links and usage, and rough handling through hedges, fences, etc. Therefore, it becomes necessary to check the length of the chain before commencing the survey work, Before checking, it should be ensured that its links are not bent, rings are circular, openings are not too wide and mud is not clinging to them. Specification When a tension of 80 N is applied at the ends of the chain and compared against a certified steel band (tape), standardized at 20°C, every metre: length should be accurate to within +2 mm. The accuracy of an overall length of 20 m chain should be within +5 mm and that of a 30 m chain within + 8mm.SR SUV late Procedure Two pegs ata required distance of 20 or 30m m are inserted ona flat ground (Fig. 2.4). The overall length of the chain is compared with the marks and the difference is noted. Marks, + 20 er 30 m —_—_—+| Fig. 2.4 Testing 20/30 chain If the chain is found to be too long, it may be adjusted by closing the opened joints of rings; reshaping the elongated links; removing one or more circular rings; and replacing the worn out rings. If chain is found too short, it may.be adjusted by straightening the bent links; flattening the circular rings; replacing circular rings by bigger rings; and inserting additional rings. 2.4 TAPES ‘Tapes are available in a variety of materials, lengths and weights. The different types of tapes used in general are discussed below. Cloth or Linen Tape These are closely woven linen or synthetic material and are varnished to resist the moisture. These are available in lengths of 10-30 m and widths of 12-15 mm. The disadvantages of such a tape include: (1) it is affected by moisture and gets shrunk; (2) its length gets altered by stretching; and (3) itis likely to twist and does not remain straight in strong winds. Metallic Tape It is a linen tape with brass or copper wires woven into it longitudinally to reduce stretching. As it is varnished, the wires are not visible. These are available in lengths.of 20-30 m. It is an accurate measurement device and is commonly used for measuring offsets. As it is reinforced with wires, all the defects of linen tapes are overcome. Steel Tapes These are 1-50 m in length and are 6-10 mm wide. At the end of the tape a brass ring is attached, the outer end of which is zero point of the tape. Steel tape cannot be used in ground with vegetation and weeds. Invar Tape This is made of an alloy of nickel (36%) and steel, having very low coefficient of thermal expansion (0.122 10 -°/°C). These are available in len; gths of 30, 50 and 100 mand in a width of 6 mm. The advantages and disadvantages of an invar tape are as follows: Advantages . Highly precise. 2. Itis less affected by temperature changes when compared to the other tapes.Disadvantages 1. Itis soft and so deforms easily. 2. Itrequires much attention in handling. 2.5 ACCESSORIES FOR CHAINING In addition to the equipments (chains and tapes), accessories, e.g. pegs, arrows, ranging rods, offset rods and plumb bob are required for chaining operations. 2.5.1 Pegs These are used to mark definite points on the ground either temporarily or semi- permanently. The exact point to and from which the measurements are to be taken, or over which an instrument is to be set, is often necessary to indicate on a peg. For this, a nail or a brass stud is driven into the flat top of the peg. The size of a peg depends on the use to which the pegs are to be put and the nature of the ground in which they are to be driven. Generally, hard creosoted wood 2.5-7.5 cm’ ? and 15-90 cm long, flat at one end and pointed at the other end are used. For temporary use, pegs of nearly round section are cut from the standing trees and then are pointed at one end and flattened at the other end. Iron or tubular pegs are made of cut pieces of about 1-2 cm in diameter. Though expensive and troublesome to carry, these pegs are preferred since they last longer. For permanent marking of stations, a small concrete pillar is used as a peg. The size varies from 15 to 30cm? and 7.5 to 60cm in height and is builtin situ. 2.5.2 Arrows These are also known as chaining pins and are used to mark the end of each chain during the chaining process. These are made of hardened and tempered steel wire 4mm in diameter. The length of an arrow is kept at 400 mm. These are pointed at one end whereas a circular ring is formed at its other end, as shown in Fig. 2.5, to facilitate carrying from one station to another. As the arrows are placed in the ground after every chain length, the number of arrows held by the follower 49, 8SWG Ih Fig. 2.5 Arrowindicates the number of chains that have been measured. This provides a check over the length of line as entered in the field notes. Fig. 2.6 Ranging rod 2.5.3 Ranging Rods These are also known as flag poles or lining rods. These are made of well- seasoned straight grain timber of teak, deodar, etc., or steel tubular rods. These are used for marking a point in such a way that the position of the point can be clearly and exactly seen from some distance away. These are 30 mm in diameter and 2 or 3 m long. These are painted with alternate bands of either red and white or black and white of 200 mm length so that on occasions the rod can be used for the rough measurement of short lengths. A cross-shoe of 15 mm length is provided at the lower end. A flag painted red and white is provided at the top, as shown in Fig. 2.6. These rods are used as signals to indicate the locations of points or the direc- tion of lines. Also, these are used to locate the intermediate points between the: two end stations when the length of the line to be measured is more than the chain length. For this purpose line ranger (Sec. 2.6) may also be employed. 2.5.4 Offset Rods These are similar to ranging rods except at the top where a stout open ring recessed hook is provided, as shown in Fig. 2.7. Itis also provided with two short narrow vertical slots at right angles to each other, passing through the centre of the section, at about eye level.Narrow slot ‘White band Black/red band Shoe Fig. 2.7 Offset rod It is mainly used to align the offset line and measuring the short offsets. With the help of hook provided at the top of the rod, the chain can be pulled or pushed through the hedges or other obstructions, if required. Offsets may also be made in the field with the help of cross-staff (Sec. 2.7) or optical square (Sec. 2.8). 2.5.5 Clinometer It is an instrument used for measuring the angle of a slope. There is a variety of forms of which the simplest one consists of a graduated semicircle resembling a protector, as shown in Fig. 2.8. A plumb bob is suspended from its centre. Two sight pins A and B are attached along the side of the upper straight diametrical { portion. ae Fig. 2.8 Clinometer To use the clinometer, a mark is made on the ranging rod at the eye level. The assistant is directed to go up or down the slope along with the ranging rod, as the case may be. The surveyor holds the clinometer at the eye level and sees the mark .on the ranging rod through the sight pins. The surveyor then clips the thread of theplumb bob with the thumb and notes the graduation below the thread. This value is the required angle of slope. 2.5.6 Plumb Bob It is made of steel in a conical shape, as shown in Fig. 2.9. It is used while measuring distances on slopes and in all the instruments that require centering. Before starting the work, it should be ensured that there are no undesirable knots in the thread of the plumb bob. Thread Fig. 2.9 Plumb bob 2.6 LINE RANGER Tt is a small instrument used to establish intermediate points between two distant points on a chain line without the necessity of sighting from one of them. It consists of two right angled isosceles triangular prisms or two plane mirrors placed one above the other, with their reflecting surfaces normal to each other, as shown in Fig. 2.10(a). One of the prisms is made adjustable to secure the necessary perpendicularity between the two reflecting surfaces, Let there be two signals A and B on a chain line and C be the intermediate point to be established in line with A and B. The surveyor stands approximately in line with A and B and brings the instrument to his eye level. The instrument is tumed so that the surveyor sees the image of one of the signals say A, through the upper prism. The surveyor then moves forward or backward, i.e. at right angles to the chain line AB turning the instrument if necessary so as to keep signal A in view, and until he observes the image of signal at B through the lower prism. Thus the images of the two signals at A and B are seen directly through the upper and lower prisms. (b) (c) Fig. 2.10 Line rangerIf point C is not in line with A and B, the two images viewed may be separated as shown in Fig. 2.10(b). If so, the surveyor moves backward or forward till the two images coincide as shown in Fig. 2.10(c). The required point C is then vertically below the centre of the instrument. o—, (a) (b) Open cross-staff French cross-staff Adjustable cross-staff Fig. 2.11 Type of cross- staff 2.7 CROSS-STAFF Itis essentially an instrument used for setting out right angles. In its simplest form itis known as Open Cross-Staff (Fig. 2.11(a)). It consists of two pairs of vertical slits providing two lines of sight mutually at right angles, Another modified form of the cross-staff is known as French Cross-Staff (Fig. 2.1 1(b)). This consists of an octagonal brass tube with slits on all eight sides. This has a distinct advantage over the open cross-staff as with it even lines at 45° can be set out from the chain line. The latest modified cross-staff is the Adjustable Cross-Staff (Fig. 2.11(c)). It consists of two cylinders of equal diameter placed one above the other. The upper cylinder can be rotated over the lower one graduated in degrees and its subdivisions. The upper cylinder carries the vernier and the slits to provide a line of sight. Thus, it may be used to take offsets and to set out any desired angle from the chain line. 2.7.1 Taking Offsets from a Cross-Staft To find the foot of a perpendicular from a given point to a chain line, the cross- staff is held vertically on the chain line approximately near the point where the offset is likely to fall. The cross-staff is turned until the signal at one end of the chain line is viewed through one pair of slits. The surveyor then takes a round and views through the other pair of slits. If the point to which the offset is to be taken is seen, the point below the instrument is the required foot of the offset. On theother hand, if the point is not seen, the surveyor moves along the chain line, without twisting the cross-staff, till the point appears. 2.7.2 Setting out a Right Angle from Chain Line with a Cross-Staft The surveyor stands at the point from where the right angle is to be set out on the chain line. The surveyor then views through one set of the slits, twists the cross- staff until a signal at one of the end of chain line appears. Then without twisting the cross-staff, he takes a round and views through the other pair of slits. The surveyor then directs the assistant to fix a signal in line with the line of sight provided. The foot of the signal is marked and joined with the point on chain line. 2.8 OPTICAL SQUARE This is a compact hand instrument to set out right angles and is superior to the cross-staff. It is a cylindrical metal box about 50 mm in diameter and 12.5 mmin depth. Figure 2.12 shows the plan of its essential features. It has two oblong apertures C’ and D’ on its circumference at right angles to each other. E is a small eye-hole provided diametrically opposite to C’. Fig. 2.12 Optical square The instrument is equipped with two mirrors A and B inclined at an angle of 45° to one another. The mirror A is known as horizon mirror, the upper half of which is silvered, whereas the lower half is a plane glass. This is placed opposite to the eye-hole E and is inclined to the axis of the instrument EC at an angle of 120°. The other mirror B is known as index mirror. It is completely silvered and is placed diametrically opposite to the aperture D’. It is kept inclined at an angle of 105° to the index sight BD of the instrument, To an eye placed at E, the signal C is visible directly through the transparent half of the horizon mirror. At the same time, the signal D is seen in the silvered portion of the horizon mirror after being reflected through the index mirror B.2.8.1 Principle The instrument is based on the principle that a ray of light reflected successively from two surfaces undergoes a deviation of twice the angle between the reflecting surfaces. 2.8.2 Taking Offsets with an Optical Square Let EC be a survey line which is required to find the foot of the perpendicular to the chain line from a given point D (Fig. 2.13). The surveyor stands on the chain line EC, near the expected point on the chain line, and observes the signa! C through the unsilvered portion of the horizon mirror and simultaneously observes the image of the signal D through its silvered portion. He then moves along the chain line until the signal C seen directly and the image of signal D coincide. The point vertically below the instrument is the foot of the required perpendicular. 2.8.3 Setting Out a Right Angle from Chain Line with an Optical Square Suppose the optical square is required to set out a perpendicular from a point H on achain line EC, to a curved boundary, as shown in Fig. 2.13, The surveyor stands at H with the optical square at the eye level and turns it until a signal at C is seen directly through the transparent portion of the horizon mirror. The curved boundary will also be visible through the silvered portion of the horizon mirror. The surveyor then directs the assistant at the curved boundary to move left or right until the signal D held by the assistant appears to coincide exactly with the signal C seen directly. The line HD will be the required perpendicular to the chain line EC. u Regu D eget ines Fig. 2.13 Offset with optical square Note While using the optical square, it should be ensured that it is held horizon- tally. Its use is restricted to fairly level ground. 2.8.4 Testing and Adjusting an Optical Square Object To place the mirrors at 45° to each other so that the aagles set out are the right angles.Test 1, Range outa straight line AC (Fig. 2.14) on a fairly level ground. 2. The surveyor stands at B, sights a signal at C and sets out aright angle, say ABD. \ 2p bd Fig. 2.14 Adjusting optical square 3. The instrument is turned and the surveyor at B sights the signal at A. 4. If the instrument is in adjustment, the image of the signal at D, will ap- pear to coincide with the signal at A. Adjustment 1. If the image of the signal at D, does not coincide with the signal at A, mark a point D, so that its image coincides with the signal at A. 2. Fix a signal at D exactly midway between D, and D). 3. The index mirror which is adjustable is turned until the image of the sig- nal D is made coincident with the signal at A. Signals at C and D are sighted again and now these should appear to coincide. 2.9 PRISM SQUARE 4. It is based on the same principle as the optical square and is used in the same manner. It has an advantage over the optical square in that no adjustment is required, since the angles between the reflecting surfaces of prisms is kept fixed (45°) as shown in Fig. 2.15. Fig. 2.15 Prism square