PRINCIPLES AND CLASSIFICATIONS OF SURVEYING

PRINCIPLES AND CLASSIFICATIONS OF SURVEYING

1     Basic Principles of surveying

a) Working from whole to part: 

The main principle of surveying whether plane or geodetic is to work from the whole to the part. This implies a precise control surveying as the first consideration followed by subsidiary detail surveying. Due to this, error arising in a place is limited to small space and is not spread (localization of error). It prevents the accumulation of errors.

If survey is carried out from the part to the whole, the errors would expand to greater magnitude and the scale of the survey will be destroy beyond control.

 for example: Area to be surveyed contain number of spread control points called primary control point was establish with a high level of precision. To fill the gap between them Secondary cps established with lesser precision than the primary CPs (Control Points).

 b) Locating of a point with reference of two other points:

There must be at least two reference points for determining positions

of any points. The location of point can be established by measurement of angles and distances. There is various method to locate points are: Triangulation, Traverse, offset, Trilateration etc.

 

 

Let P and Q be two given control points. Any other point, say, R can be located with reference to these points, by any one of the following methods:

 

(a)  By measuring the distances PR and QR. The distances PR and QR may be measured and the location of R may be plotted by drawing arcs to the same scale to which line PQ has been drawn (Fig. (a)).

 

(b)  Offsetting: By Dropping a perpendicular from Ron PQ. A perpendicular RT may be dropped on the line PQ. Distances PT, TQ and RT are measured and the location of R may be plotted by drawing the perpendicular RT to the same scale to which line PQ has been drawn [Fig. (b)).

Principles (a) and (b) are generally used in the method of Chain surveying'.

 

(c) By measuring the distance QR and the angle PQR. The distance QR and the angle PQR equal to a are measured and the location of R may be plotted either by means of a protractor or trigonometrically [Fig. (c)).

This principle is used in the method of Theodolite 'Traversing'.

 

(d) By measuring the interior angles of the triangle PQR. The interior angles P, Q and R of the triangle PQR are measured with an angle-measuring instrument such as theodolites. The lengths of the side’s PR and QR are calculated by solving the triangle PQR and the coordinates of R is calculated in the same terms as those of P and Q. Even without calculating the co-ordinates, or sides the location of R can be obtained by plotting the angles POR and QPR [Fig. (d)].

This principle is used in the method of 'Triangulation'.

 

(e) By measuring the sides of the triangle PQR. The interior angles P and R are calculated from the measured sides of the triangle POR by applying cosine rule.

This principle is used in the method of Trilateration.

c) Accuracy of work / Economy of Accuracy:

While performing work for any purpose we have to try to achieve the desired accuracy. High accurate work was taken in action whereas low accurate work not in use. If accuracy achieved is higher than the accuracy required, then the method adopted is obviously expensive & have meaning.

for example: Use of wild T3 Theodolite for establishing 4th order CPs is beyond of this principle.

 d) Independent check in → 

In this we talk about measurement, we have to measure all possible values to find out error, instead of dependent on mathematical computation.      for example:  In Triangulation, third angle can be computed mathematically depending upon the two observed angles, but the third angle is measured

independently;

In compass survey B.B. can be obtained from F.B. but both f.B. & B.B measured

e) Consistency in work

 In any survey work if there is more than one measurement to be carried out. both of the measurement should be on same accuracy. If angular & linear measurement are measured than both will be in same accuracy. In this we do not compare achieved accuracy verses accuracy required, but we compare accuracies of different measurement. In this we also talk about precautions to be followed and time of period to carry any survey work.

for example:  If wild t3 Theodolite used for measuring angle, distance should be measured by EDM, then only accuracy achieved

 

2    Primary Division of Surveying

Primary division of surveying is made on the basis whether the curvature of the earth is considered or whether the earth is assumed to be a flat plane. the actual shape of the earth is an oblate spheroid. It is an ellipsoid of revolution, flattened at the poles and bulging at the equator. The length of the polar axis is about 12713.168 km and that of the equatorial axis is about 12756.602 km, as computed by Clark in 1866. Thus, the polar axis is shorter than the equatorial axis by about 43.434 km. Relative to the diameter of the earth, the difference in the lengths of the two axes is a very small quantity, about 0.34%. The students understanding is greatly facilitated by assuming the earth to be an approximate sphere.

     (classification based on desired accuracy)

a)  plane surveying

b)  Geodetic surveying

a)    Plane Surveying

The type of surveying in which the mean surfaces of the earth is considered as a plane and the spheroidal surface is neglected, are known as plane surveying. In this survey all triangles formed by survey lines are considered as plane triangles, the level line is considered as straight lines and all plumb lines are considered as parallel lines.  This type of survey prefers for small area and high

accuracy of work is not required. It is done on area less than 260 Sq.km. 

Scope and Use of Plane Surveying: Plane surveys which generally cover areas up to 260 sq. km, are carried out for engineering projects on sufficiently large scale to determine relative positions of individual features of the earth surface.

Plane surveys are used for the lay-out of highways, railways, canals, fixing boundary pillars, construction of bridges, factories etc. The scope and use of plane surveys is very wide. For majority of engineering projects, plane survey. ing is the first step to execute them. For proper, economical and accurate planning of projects, plane surveys are basically needed and their practical significance cannot be over-estimated.

b)    Geodetic Surveying

The type of survey in which the shape of the earth is taken into account and higher degree of accuracy in linear as well as angular observations is achieved, are known as 'Geodetic Surveying'. All lines lying in the surfaces are curved lines and the triangles formed are spherical Triangles. Therefore, it involves spherical Trigonometry. Geodetic survey includes work of larger magnitude and higher degree of precision. It is done on area more than 260 sq.km. It is used for finding shape of earth, distance between two continents etc.  Geodetic surveys are usually carried out by the department of National Surveys.

 Scope and use of Geodetic Surveying. Geodetic surveys are conducted with highest degree of accuracy to provide widely spaced control points on the earth's surface for subsequent plane surveys. Provision of such control points, is based on the principle of surveying from the whole to the part and not from the part to the whole. Geodetic surveys require the use of sophisticated instruments, accurate methods of observations and their computation with accurate adjustment. These surveys are generally carried out to provide plan control. To eliminate the errors in observations due to atmospheric refraction, angular observations are generally restricted to nights and lamps are used as signals on the survey stations.

3    Classification of Surveys

According to the use and the purpose of the final maps, surveys may be classified, under the following different heads.

 3.1 Based upon the nature of field survey; -

1. Land survey: 

It consists of re-running old parcel lines to determine their lengths and directions, subdividing the parcel into predetermined shapes and sizes and calculating their areas and setting monuments and locating their positions. Topographical, cadastral and city surveys are some of the examples of land surveying.

  i)  Topographical Survey: -

The process of determining the relative position of points (places) on the earth's surface by measuring horizontal distances differences in elevation of directions (linear angular measurement) and is made to determine the natural and manmade features, are called Topographical survey. It deals with planimetric as well as altimetric information.

  ii)  City Survey: -

 The surveys which are carried out for the construction of roads, parks, water supply system, sewer and other constructional work for any developing township, are called City surveys. The city maps which are prepared for the tourists are known as Guide Maps.

  iii)  Cadastral Survey: -

The survey which is carried out to fixing of property lines, the calculation of land area, or the transfer of land property from one owner to another, are known as Cadastral Survey. They are also made to fix the boundaries of municipalities, states and federal Jurisdictions,

2.  Marine Survey:

The surveys which deal with the mapping of large water bodies for the purpose of navigation, construction of harbour works, prediction of tides and determination of mean sea-level, are called Hydrographic surveys. Hydrographic surveys consist of preparation of topographical maps of the shores and banks, by taking soundings and determining the depths of water at a number of places and ultimately surveying bathymetric contours under water.

 3.   Astronomical Survey

The surveys which are carried out for determining absolute locations i.e. latitudes of different places on the earth surface and the direction of any line on the surface of the earth by making observations to heavenly bodies, i.e. stars and sun, are called astronomical surveys. In northen hemisphere, when night observations are preferred to, observations are usually made to the Polaris, i.e. the pole star.

3.2.  Based on the purpose of the survey:

(1)  Engineering Survey:

The surveys which are carried out for determination of quantities or to afford sufficient data for designing engineering works, such as roads, reservoirs, sewage disposal, water supply, etc., are called Engineering Surveys.  It consists of topographic survey of the area, measurement of earth work, providing grade, and making measurements of the completed work till date. These are also known as construction surveys.

(2)  Military or Defence Survey:

The surveys which are carried out for preparation of maps of the areas of Military importance, are called military surveys. Surveys have a very 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 preparing tactical and strategic plans both for defence and attack. 

(3)  Mine Survey:

The surveys which are carried out for exploration of mineral wealth beneath the surface of the ground, i.e., coal, copper, gold, iron ores etc., are called Mine surveys. In this both surface and underground survey 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 constructing the underground plans, fixing the positions and directions of tunnels, shafts, drifts, etc., and preparation of a geological map.

(4)  Geological Survey:

The surveys which are carried out to ascertain the composition of the earth crust i.e. different stratas of rocks of the earth crust, are called Geological surveys.  In this both surface and subsurface surveying is required 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. These are also required to decide upon the foundation treatment of important engineering projects such as dams and bridges.

(5)  Archeological Survey:

The surveys which are carried out to prepare maps of ancient culture i.e.   antiquities, are called Archeological surveys. These are done to unearth the relics of antiquity, civilizations, kingdoms, towns, villages, forts, temples, etc., buried due to earthquakes, 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.

 (6) 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 irrigation, physiographic regions and waterfalls, surface drainage, slope height curve and slope profile and contours.

(7)   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 sequence of operations in a route survey is as follows: 

  (a) Reconnaissance survey:

 A visit is made to the site and all the relevant information 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.

 (b) Preliminary survey :

It is the topographical survey of the area in which the project is located. Sometimes an aerial 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.

 (c) Control survey :

It consists in planning a general control system for preliminary survey which may be triangulation or traversing. For location survey, it consists of triangulation. 

(d) 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.

 

3.3.  Based on instruments used:

According to the instruments used and method of surveying, method surveys may also be classified as under:

1.   Chain survey: -

 When a plan is to be made for a 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 because 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 development of buildings, roads, water supply and sewerage schemes.

 

2.   Compass survey: -

 The branch of surveying in which direction of survey lines are determined by a compass and their lengths by chaining or tapping directly on the surface of the earth, is called compass survey. Method of chain survey is preferred to, if the area to be surveyed is small in extent and higher accuracy is aimed at. On the other hand, if the area is comparatively large, with undulations, compass survey is adopted. Before recommending the compass survey for any area, it must be ascertained that area is not magnetically disturbed.

 

3.   Plane table survey: -       

 It is a graphical method of surveying in which field work and plotting are done simultaneously. 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 necessary measurement, the field being in view while plotting. The details like boundaries, 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.

                                    

4.   Theodolite survey: -

    An instrument used for measuring horizontal and vertical angles accurately, is known as a theodolite. Theodolite is also used for prolongation of survey lines, finding difference in elevation and setting out engineering works requiring higher precision.

  The survey carried out by theodolite is by theodolite traverse. When the linear measurements are done with chain and tape and the directions or angles are measured with theodolite 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 accurately 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.

 

5.   Tachometric survey: -

This is a method of surveying in which both the horizontal 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 inaccessible. It is usually recommended for making contour plans of building estates, reservoirs, etc.

 

6.   Triangulation survey: -

when the area to be surveyed is of considerable extent, triangulation 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,

using sine formula. 

 

 

 7.   Total-station surveying: -

The electronic theodolites combined with EDMs and electronic data collectors are called total stations. A total station reads and records horizontal and vertical angles, together with slopes distances. The instrument has capabilities of calculating rectangular coordinates of the observed points, slope corrections, remote object elevations, etc. The surveys carried out using total station are called total station survey

 8.   Photogrammetric surveying.

Photogrammetric surveying or photogrammetry is the branch of surveying in which map are prepared from photo-graphs taken from ground or air station. With an advancement of the photogrammetric techniques, photographs are also being used for the interpretation of geology, classification of soils and crops.

9.    Satellite based survey: -

 Remote sensing and global positioning system (GPS) are the satellite-based surveys. Acquiring data for positioning on land, on the sea, and in space using satellite-based navigation system based on the principle of trilateration is known as GPS. Global positioning system uses the satellite signals, accurate time and sophisticated algorithms to generate distances in order to triangulate positions. In remote sensing, the data about an object is collected by sensors placed on satellites by employing electromagnetic energy as the means of detecting and measurements.

10. EDM Survey:

This is the electronic method of measuring distances using the propagation, reflection and subsequent reception of either light or radio waves. The examples of EDM instruments are tellurometer, geodimeter, distomat, etc.

11. 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 planning a constructional project, irrespective of its extent, that is, 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 achieved by collecting complete information regarding the relative heights of the ground by levelling.

Technical terms

The following technical terms are generally used in surveying:

(1)  Plan.

A plan is the graphical representation of the features on the earth surface or below the earth's surface as projected on a horizontal plane. This may not necessarily show its geographical position on the globe. On a plan, horizontal distances and directions are generally shown.

(2)  Map.

The representation of the earth surface on a small scale, is called a map. The map must show its geographical position on the globe. On a map the topography of the terrain, is depicted generally by contours, hachures and spot levels.

(3)  Topographical map.

 The maps which are on sufficiently large scale to enable the individual features shown on the map to be identified on the ground by their shapes and positions, are called topographical maps.

(4)  Geographical maps.

The maps which are on such a small scale that the features shown on the map are suitably generalized and the map gives a picture of the country as a whole and not a strict representation of its individual features, are called Geographical maps.