Introduction of Surveying

Introduction of surveying

 1. Surveying and mapping.

Surveying is the science and art of determining the relative positions of various points above, on or below the surface of the earth. The relative positions are determined by measuring horizontal distances, vertical distances (elevations), horizontal angles and vertical angles accurately using various surveying instruments. After taking the measurements in the field, computations are done and the plans and maps are prepared in the office. These plans and maps are used for planning of engineering works, marking of boundaries, computations of areas and volumes, and various other purposes. Surveying also includes the art of setting out or locating the points on the ground from the plan or map.

So, surveying can be done by different methods some of them are listed below:

1. 1.     Land surveying.

2.     Engineering surveying.

3.     Mining surveying.

4.     Hydrographic surveying.

5.     Geodetic surveying.

6.     Photogrammetry and remote sensing

Surveying and Mapping:

Surveying or land surveying is the technique, profession, and science of determining the terrestrial or three-dimensional position of points and the distances and angles between them. after surveying by different method our mission is to produce a map.

Surveying, although simple in concept, requires great skill and practice for doing the work accurately and economically. It requires basic knowledge of various disciplines such as mathematics, physics, geodesy and astronomy. The need for accurate surveying is increasing rapidly with the development in technology. The construction of modern buildings, highways, railways, high dams, long bridges, and tunnels requires accurate surveying. As the cost of the land and property is increasing rapidly, high accuracy is required in marking the boundaries and the land subdivision.

Map is a sheet of drawing paper where field data are plotted. It is produced in fix scale. It is last result of surveying. It can be made manually or digitally. Digitally produced map is made from GIS or AutoCAD.

The act or process of making a map is known as mapping. Mapping is representation of a region of three-dimensional space, such as of the Earth or a part of the universe, usually on a two-dimensional plane surface. See also projection. a map designed especially for navigators on water or in the air.

plan, outline, diagram, Map, Chart, Graph refer to representations of surfaces, areas, or facts. Map most commonly refers to a representation of the surface of the earth or a section of it, or an area of the sky

Surveying and mapping are done one after another. We collect required data from field and make map in office. But in plane table surveying map is made in the field. Thus, this way surveying and mapping is done.

2.  Function of surveyor

1.  Prepare and maintain sketches, maps, reports, and legal descriptions of surveys in order to describe, certify, and assume liability for work performed.
2.  Verify the accuracy of survey data, including measurements and calculations conducted at survey sites.
3.  Direct or conduct surveys in order to establish legal boundaries for properties, based on legal deeds and titles.
4.  Record the results of surveys, including the shape, contour, location, elevation, and dimensions of land or land features.
5.  Calculate heights, depths, relative positions, property lines, and other characteristics of terrain.
6.  Coordinate findings with the work of engineering and architectural personnel, clients, and others concerned with projects.
7.  Adjust surveying instruments in order to maintain their accuracy.
8.  Compute geodetic measurements and interpret survey data in order to determine positions, shapes, and elevations of geomorphic and topographic features.
9.  Establish fixed points for use in making maps, using geodetic and engineering instruments.
10.  Determine longitudes and latitudes of important features and boundaries in survey areas, using theodolites, transits, levels, and satellite-based global positioning systems (GPS).
11.  Train assistants and helpers, and direct their work in such activities as performing surveys or drafting maps

3.   Need, importance and scope of surveying

Ø The first necessity in surveying is to prepare a plan and a section of an area to be covered by the project. From these prepared maps and sections, the best possible alignment, amount of earthwork and other necessary details depending upon the nature of the project can be calculated.

Ø The planning and design of all Civil Engineering projects such as railways, highways, tunneling, irrigation, dams, reservoirs, waterworks, sewerage works, airfields, ports, massive buildings, etc. are based upon surveying measurements.

Ø During execution of the project of any magnitude is constructed along the lines and points established by surveying.

Ø The measurement of land and the fixation of its boundaries cannot be done without surveying.

Ø The economic feasibility of the engineering feasibility of a project cannot be properly ascertained without undertaking a survey work

Ø The execution of hydrographic and oceanographic charting and mapping requires.

Ø Surveying is used to prepare a topographic map of a land surface of the earth.

3.1 Needs of surveying

Surveying is needed due to the following reasons: 

1. To determine the relative position of any objects or points of the earth.
2. To determine the distance and angle between different objects.
3. To prepare a map or plan to represent an area on a horizontal plan. 
4. To develop methods through the knowledge of modern science and technology and use them in the field. 
5. To solve measurement problem in an optimal way. 

3.2 Importance of surveying 

The knowledge of surveying is advantageous in many phases of engineering. Surveying is of vital importance in any engineering project. Some of the basic importance of surveying is discussed below.

1. The first importance of surveying is to prepare a plan and a section of an area to be covered by the project. From these prepared maps and sections, the best possible alignment, amount of earthwork and other necessity details depending upon the nature of projects can be Calculated.
2.  The planning and design of engineering projects such as railways, road works, bridge, pavement marking, water works, tunnelling, irrigation etc. are based upon surveying measurements.
3. The measurement of land and the fixation of its boundaries cannot be done without surveying. 
4. Surveying is used to prepare a topographic map by doing a topographic survey of a land surface of the earth.
5. Feasibility of any engineering project cannot be properly obtained without undertaking a survey work. 

3.3 Uses of surveying

 Surveying is the scientific technique to determine the position of points and angles & distances between them. The process of surveying is used to fulfill various purposes. It is necessary for making maps, planning a project etc. To accomplish all civil engineering works or projects successfully, surveying is used. 

Some of the numerous functions of surveying are given below.

1. Topographical maps showing hills, rivers, towns, villages, forests etc. are prepared by surveying.

2. For planning and estimating new engineering projects like water supply, irrigation schemes, mines, railroads, bridges, transmission line, buildings etc, surveying is required.

3. Cadastral map showing the boundaries, a field houses and other properties are prepared by surveying

4. Engineering map showing the position of engineering works like roads, railways, buildings, dams, canals etc. are prepared through surveying.

5.  To set out a work and transfer details from map to ground, knowledge of surveying is used.

6.  For planning navigation routes and harbours, marine and hydrographic, surveying are used.

7.  To help military strategic planning, military maps are prepared by surveying

8.  For exploring mineral wealth, mine survey is necessary

9. To determining different strata in the earth crust, geological surveys are required.

10. Archaeological surveys are used to unearth relics of antiquity. 

3.4    Scope of surveying

 Scope of surveying is broad in the field of civil and geomatics engineering. Surveying may be used in various other fields as described below in short

1. Control surveying: To establish horizontal and vertical positions of control points.

2.  Land surveying: To determine the boundaries and areas of parcels of land, also known as property survey, boundary survey or cadastral survey. 

3. Topographic survey: To prepare a plan/map of a region which includes natural as well as man-made features including elevation.

4.  Engineering survey: To collect requisite data for planning, design and execution of engineering projects. Three broad steps are 

• Reconnaissance survey: To explore site conditions and availability of infrastructures. 
•  Preliminary survey: To collect adequate data to prepare a plan/map of area to be used for planning and design. 
•  Location survey: To set out work on the ground for actual construction/execution of the project. 

5. Route survey: To plan, design, and lying out routes such as highways, railways, canals, pipelines, and other linear projects.

•  Construction surveys: Surveys which are required for establishment of  points, lines, grades, and for staking out engineering works(after the plans have been prepared and the structural design has been done).
• Astronomic surveys: To determine the latitude, longitude (of the observation station) and azimuth (of a line through observation station) from astronomical observation 
•  Mine surveys: To carry out surveying specific for opencast and underground mining purposes

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4.   Objective of surveying

Surveying is the means of determining the relative positions of points and the relative distance. The objective of surveying may vary depending on the types of project. The surveyor must be clear about the objectives of surveying. 

The main objectives of surveying are discussed below:

Ø To determine the relative position of any objects or points of the earth.

Ø To determine the distance and angle between different objects.

Ø To prepare a map or plan to represent an area on a horizontal plan.

Ø To develop methods through the knowledge of modern science and the technology and use them in the field.

Ø To layout or to mark the position of the proposed structures on the ground.

Ø To determine areas, volumes and other related quantities.

Ø To solve measurement problems in an optimal way.

5.  General procedures of surveying and method.

The surveying work is divided into two parts:

 1) Field work.

2) Office work.

 

The procedure in field are as follows:

a) Reconnaissance

b) Established control points.

c) Signaling.

d) Adjustment of instrument.

e) observation.

 f) Recording.

The office work are as follows:

 a) planning.

b) computation.

 c) plotting.

 

 

 The method of surveying are as follows:

 1) Traverse.

 2) Triangulation.

3) Trilateration.

4) Satellite survey.

 5) Aerial survey.

 6.Surveying Concepts:

 6.1  Distance and Direction

•  Distance is a numerical measurement of how far apart objects or points are.
•  Direction is the angle from the reference line to ta target.
•  In survey reference line means north line and target means survey line. The angle formed is bearing. Thus, bearing is the angle formed between reference line and survey line is bearing. We can easily find the position of a point by distance and angle.
•  There are four direction east, west, north and south and further it is divided into four division SE, NE, SW, NW.

 

6.2  Shape and size of earth

 The earth is not a true sphere and slightly flattened at the pole. Its polar axis is somewhat smaller in length (about 43.45km) 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 pole is 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 sightly elliptical and therefore such a figure should be called an ellipsoid. Precise observation indicate that the southern Hemisphere is larger than the northern. Therefore, all the polar section is oval and can be called ovaloid.

In fact, no geometrical solid represent the true shape of the earth. 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. The earth is also recognized by a geoid.

 

 6.3  Curvature of the earth.

 In case of long sight, the horizontal line is not a level line due to curvature of earth. The vertical distance between a horizontal line and the line represents the effect of curvature of earth.

 

Figure. 

 

 

In the figure let AB be a level line through A, and O be the center of the earth. A is the instrument position. AC, the line of collimation, will be the horizontal line.

R is the radius of the earth.

The curvature correction Cc=BC

Now OC²=OA²+AC²

or, (R+Cc) ²=R²+D²

Or, R²+2R*Cc+Cc²=R²+D²

Or, Cc(2R+Cc) =D²

 Or, Cc=D²/2R+Cc

Since Cc is very small as compared to the radius of earth

R Cc=D²/2R

Taking the radius of the earth as 6379 KM

Cc=0.0785D² where D= distance in KM

Since the curvature increase the staff reading the correct is subtractive.

True staff reading =observed staff reading_0.0785D².

 

6.4  Spheroid and Geoid

If any two of the three axes of that ellipsoid are equal, the figure becomes a spheroid. If all three are equal, it becomes a sphere. Geoid is the equipotential gravity surface of the earth at mean sea level. At any point it is perpendicular to the direction of gravity.

 

6.5  Earth figure elements.

1)    Axis of earth.

2)    Great circle.

3)    Equator.

4)    Parallels and meridian.

5)    Flattening

6.5.1  Axis of earth

 The axis of the earth is an imaginary line around which earth rotates. It passes through north pole, center of the earth and south pole. It is tilted and makes angle of 66.50 degree with orbital plane.

Everest spheroid is use for Nepal in which semi -major axis, semi-minor axis and flattening value is

Semi-Major axis(a) =6377276.345m

Semi-Minor axis (b) =6356075.413m

Flattening(1/f) =300.8017 •

Flattening is a measure of the compression of a circle or sphere along a diameter to form an ellipse or an ellipsoid of revolution (spheroid) respectively

 Flattening=a_b/a.

 

 6.5.2   Great circle

 Imagine a plane passing through the center of the earth. The intersection of such plane with the mean level surface of earth is termed as great circle of the earth.

6.5.3  Equator

 The Equator lies exactly between the Poles at 0°. We refer to the Area above the equator as the Northern Hemisphere and below, the Southern Hemisphere.

 The Sun is directly overhead at the equator at the Equinoxes on 2 days of the year.

 

6.5.4  Meridian and parallels

1.  It is the line defined by the intersection of the imaginary plane passing through the poles.
2.  It is also known as the reference line to measure bearing.
3.  Bearing is clockwise or anticlockwise angle from reference meridian to the survey line.
4.  Parallels are the imaginary line where meridian are perpendicular. It is a section parallel to the equator.

 

 Types of meridian

1)    Arbitrary meridian

2)    Grid meridian

3)    Magnetic meridian

4)    True meridian

 

 

 6.6  Coordinate and coordinate system.

 Coordinate is one or more number which determines the position of a point.

 A coordinate system is used to determine the relative position of points within the survey area or, in many cases, with respect to a much larger area.

 

Types of coordinate system:

1)  Geographical coordinate system.

 It is mostly use coordinate system to denote the position of the earth. Here the notation is done in degree eg 85°42'E, 27°19'N. Here position is determined by latitude, longitude, elevation. Height is represented in metre.

 

2)  rectangular coordinate system.

 In this system position is determined by xyz coordinate x-(Easting) y_(Northing) z_(elevation)

6.7  Latitude, Longitude, Height above MSL:

 Latitude

 Latitude is a co-ordinate on the Earth's surface that measures how far north or south a position is. It is a co-ordinate measured from 0° at the Equator to +90° at the North Pole or -90° at the South Pole. Sometimes these are shown as 90N or 90S. The Equator and Tropics are lines of latitude.

 

 Longitude

 0° is the line of longitude that intersects the poles with the Greenwich Prime Meridian. We measure the longitude co-ordinate up to 180° west or east of Greenwich.On the opposite side of the world from the Greenwich Meridian is another line of longitude is called the International Dateline.

 

6.8 Projection

 a map projection is a way to flatten a globe's surface into a plane in order to make a map. The curve surface is transfer into ta paper so there will be distortion. So as possible we should minimize the distortion.

 

6.9Relief representation

 The method of showing the height difference of the earth in known as relief representation.

 

Types of relief representation:

1. Contouring
2. Hachures
3. Hill shading
4. layer tilting
5. Spot height.

 

7.  End product of map

1.   Coordinate
2.   Height
3.   Distance
4.   Bearing
5.  Map or plan