01-INTRODUCTION TO SURVEYING
INTRODUCTION TO SURVEYING
Surveying is defined as “taking a general view of, by observation and measurement determining the boundaries, size, position, quantity, condition, value, etc. of land, estates, building, farms mines, etc. and finally presenting the survey data in a suitable form”. This covers the work of the valuation surveyor, the quantity surveyor, the building surveyor, the mining surveyor, and so forth, as well as the land surveyor. Another school of thought defines surveying “as the act of making measurement of the relative position of natural and manmade features on earth?s surface and the presentation of this information either graphically or numerically.
The process of surveying is therefore in three stages namely:
This part of the definition is important as it indicates the need to obtain an overall picture of what is required before any type of survey work is undertaken. Inland surveying, this is achieved during the reconnaissance study.
Observation and Measurement:
This part of the definition denotes the next stage of any survey, which in land surveying constitutes the measurement to determine the relative position and sizes of natural and artificial features on the land.
Presentation of Data:
The data collected in any survey must be presented in a form that allows the information to be clearly interpreted and understood by others. This presentation may take the form of written reports, bills of quantities, datasheets, drawings, and inland surveying maps and plan to show the features on the land.
Types of Surveying
On the basis of whether the curvature of the earth is taken into account or not, surveying can be divided into two main categories:
Plane surveying: The type of surveying where the mean surface of the earth is considered as a planeAll angles are considered to be plane angles. For small areas less than 250 km2 plane surveying can safely be used. For most engineering projects such as canal, railway, highway, building, pipeline, etc constructions, this type of surveying is used. It is worth noting that the difference between an arc distance of 18.5 km and the subtended chord lying in the earth?s surface is 7mm. Also the sum of the angles of a plane triangle and the sum of the angles in a spherical triangle differ by 1second for a triangle on the earth?s surface having an area of 196km2
Geodetic surveying: It is that branch of surveying, which takes into account the true shape of the earth (spheroid).
Classification of Surveying:
Surveying is classified based on various criteria including the instruments used, purpose, the area surveyed, and the method used. Classification on the Basis of Instruments Used. Based on the instrument used; surveys can be classified into;
i) Chain tape surveys
ii) Compass surveys
iii) Plane table surveys
iv) Theodolite surveys
Classification based on the surface and the area surveyed Land surveying Land surveys are done for objects on the surface of the earth. It can be subdivided into:
(a) Topographic survey:
This is for depicting the (hills, valleys, mountains, rivers, etc) and manmade features(roads, houses, settlements…) on the surface of the earth.
(b) Cadastral survey
It is used to determining property boundaries including those of fields, houses, plots of land, etc.
(c) Engineering survey
It is used to acquire the required data for the planning, design, and execution of engineering projects like roads, bridges, canals, dams, railways, buildings, etc.
The surveys involving the construction and development of towns including roads, drainage, water supply, sewage street network, etc, are generally referred to as city surveys.
Marine or Hydrographic Survey: Those are surveys of large water bodies for navigation, tidal monitoring, the construction of harbor.
Astronomical Survey: Astronomical survey uses the observations of the heavenly bodies (sun, moon, stars, etc) to fix the absolute locations of places on the surface of the earth
CLASSIFICATION ON THE BASIS OF PURPOSE
i) Engineering survey
ii) Control Survey: The control survey uses geodetic methods to establish widely spaced vertical and horizontal control points.
iii) Geological Survey: A geological survey is used to determine the structure and arrangement of rock strata. Generally, it enables us to know the composition of the earth.
iv) Military or Defense Survey: It is carried out to map places of military and strategic importance
v) Archeological survey is carried out to discover and map ancient/relies on antiquity.
Classification Based On Instrument Used
i. Chain/Tape Survey: This is the simple method of taking the linear measurement using a chain or tape with angular measurements made.
ii. Compass Survey: Here horizontal angular measurements are made using a magnetic compass with the linear measurements made using the chain or tape.
iii. Plane table survey: This is a quick survey carried out in the field with the measurements and drawings made at the same time using a plane table.
iv. Leveling: This is the measurement and mapping of the relative heights of points on the earth?s surface showing them in maps, planes, and charts as vertical sections or with conventional symbols.
v. Theodolite Survey: Theodolite survey takes vertical and horizontal angles in order to establish controls.
CLASSIFICATION BASED ON THE METHOD USED:
i. Triangulation Survey:
In order to make the survey, manageable, the area to be surveyed is first covered with a series of triangles. Lines are first run around the perimeter of the plot, then the details fixed in relation to the established lines. This process is called triangulation. The triangle is preferred as it is the only shape that can completely over an irregularly shaped area with minimum space left.
ii. Traverse survey:
If the bearing and distance of a place of a known point is known: it is possible to establish the position of that point on the ground. From this point, the bearing and distances of other surrounding points may be established. In the process, positions of points linked with lines linking them emerge. The traversing is the process of establishing these lines, is called traversing, while the connecting lines joining two points on the ground. Joining two while bearing and distance is known as traverse station in each of the points of the traverse, while the traverse leg is the straight line between consecutive stations. Traverses may either be open or closed.
1. Closed Traverse:
When a series of connected lines form a closed circuit, i.e. when the finishing point Coincides with the starting point of a survey, it is called a „closed traverse?.
2. Open Traverse:
When a sequence of connected lines extends along a general direction and does not return to the starting point, it is known as „open traverse? or (unclosed traverse).
CLASSIFICATION OF SURVEYORS:
Surveying is made up of various specializations known as sectors or classes as shown below:
1. General Practice Surveyors:
• Surveyors under this class are mostly concerned with valuation and investment. Valuation surveyors deal with property markets, land and property values, valuation procedures and property law. Investment surveyors help investors to get the best possible return form property.
• They handle a selection of properties for purchase or sale by pension funds, insurance companies, charities and other major investors. They also specialize in housing policy advice, housing development and management.
2. Planning and Development Surveyors:
• They are concerned with preparing planning applications and negotiating with local authorities? planners to obtain planning permission.
3. Building Surveyors:
• Their work involves advising on the construction, maintenance, repair of all types of residential and commercial property.
• The analysis of building defects is an important part of a building surveyor?s discipline.
• The Quantity SurveyorsThey evaluates project cost and advice on alternative proposals. They also measure that each element of a project agrees with the cost plan allowance and that the overall project remains within budget.
4. Rural Practice Surveyors:
• Surveyors in rural practice advise landowners, farmers, and others with interests in the countryside.
• They are responsible for the management of country estates and farms, the planning and execution of development schemes for agriculture, forestation, recreation, sales of properties, and livestock.
5. Mineral Surveyors:
• They plan the development and future of mineral workings. They work with local authorities and the landowners on planning applications and appeals, mining laws and working rights, mining subsidence and damage, the environmental effects of land, and deep underground mines.
6. Land surveyors:
• They measure land and its physical features accurately and record them in the form of a map or plan for the purpose of planning a new buildings and by local authorities in managing roads, housing estates, and other facilities.
• They also undertake the positioning and monitoring for construction works.
BRANCHES OF SURVEYING
1. Aerial Surveying:
Aerial surveys are undertaken by using photographs taken with special cameras mounted in an aircraft viewed in pairs. The photographs produce three-dimensional images of ground features from which maps or numerical data can be produced usually with the aid of stereo plotting machines and computers.
2. Hydrographic Surveying (Hydro-Survey):
The hydro survey is undertaken to gather information in the marine environment such as mapping out the coastlines and sea bed in order to produce navigational charts.
It is also used for offshore oil exploration and production, design, construction, and maintenance of harbors, inland water routes, river and sea defense, and pollution control.
3. Geodetic Survey:
• In a geodetic survey, large areas of the earth's surface are involved usually on a national basis where survey stations are precisely located large distances apart. The account is taken of the curvature of the earth, hence it involves advanced Mathematical theory and precise measurements are required to be made.
Geodetic survey stations can be used to map out the entire continent, measure the size and shape of the earth, or in carrying out scientific studies such as determination of the Earth?s magnetic field and direction of continental drifts.
4. Plane Surveying:
In-plane surveying relatively small areas are involved and the area under consideration is taken to be a horizontal plane. It is divided into three branches.
- Cadastral surveying
- Topographical surveying
- Engineering surveying
5. Cadastral surveying
• These are surveys undertaken to define and record the boundary of properties, legislative area, and even countries.
• It may be almost entirely topographical where features define boundaries with the topographical details appearing on ordinance survey maps.
• On the other hand, markers define boundaries corner or line points and little account may take topographical features.
6. Topographical Survey
• These are surveys where the physical features on the earth are measured and maps/plans prepared to show their relative positions both horizontally and vertically.
• The relative positions and shape of natural and man-made features over an area are established usually for the purpose of producing a map of the area of for establishing geographical information system.
7. Engineering Survey
• These are surveys undertaken to provide special information for the construction of Civil Engineering and building projects.
• This is an exhaustive preliminary survey of the land to be surveyed. It may be either ground reconnaissance or aerial reconnaissance survey.
• Reconnaissance is made on arrival to the site during which an overall picture or view of the area is obtained. The most suitable position of stations is selected, the purpose of the survey and the accuracy required will be drawn, and finally, the method of observation will be established.
Objectives of reconnaissance
1. To ascertain the possibility of building or constructing a route or track through the area.
2. To choose the best one or more routes and record on the amp
3. To estimate probable cost and draft airport.
Introduction So far, we have discussed the meaning, object, and major classifications of surveying. Now let us move further to discuss the basic principles and process of surveying. Objectives. To enable students to understand the basic principles of surveying. To expose the students to the process of surveying.
BASIC PRINCIPLES IN SURVEYING
Principle of working from whole to part
• It is a fundamental rule to always work from the whole to the part. This implies a precise control surveying as the first consideration followed by subsidiary detail surveying.
• This surveying principle involves laying down an overall system of stations whose positions are fixed to a fairly high degree of accuracy as control, and then the survey of details between the control points may be added on the frame by less elaborate methods.
• Once the overall size has been determined, the smaller areas can be surveyed in the knowledge that they must (and will if care is taken) put into the confines of the main overall frame.
• Errors that may inevitably arise are then contained within the framework of the control points and can be adjusted to it.
Surveying is based on simple fundamental principles that should be taken into consideration to enable one get good results.