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Classifications of Surveying

Posted date: 10:44 AM / comment : 0

Classifications of Surveying
Based on the purpose (for which surveying is being conducted), Surveying has been classified into:
•  Control surveying : To establish horizontal and vertical positions of control points.
•  Land surveying : To determine the boundaries and areas of parcels of land, also known as property survey, boundary survey or cadastral survey.
•  Topographic survey : To prepare a plan/ map of a region which includes natural as well as and man-made features including elevation.
•  Engineering survey : To collect requisite data for planning, design and execution of engineering projects. Three broad steps are

1)  Reconnaissance survey : To explore site conditions and availability of infrastructures.
2) Preliminary survey : To collect adequate data to prepare plan / map of area to be used for planning and design.
3)  Location survey : To set out work on the ground for actual construction / execution of the project.
•  Route survey : To plan, design, and laying out of route 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.
Principles of Surveying
The fundamental principles upon which the surveying is being carried out are
  • working from whole to part.
  • after deciding the position of any point, its reference must be kept from at least two permanent objects or stations whose position have already been well defined.
The purpose of working from whole to part is
  • to localise the errors and
  • to control the accumulation of errors.
This is being achieved by establishing a heirarchy of networks of control points. The less precise networks are established within the higher precise network and thus restrict the errors. To minimise the error limit, highest precise network (primary network) Figure 1.1 of control points are established using the most accurate / precise instruments for collection of data and rigorous methods of analysis are employed to find network parameters. This also involves most skilled manpower and costly resources which are rare and cost intensive. 

Operations in Surveying
Operations in surveying consists of :
Planning
To decide
•  the methods to be adopted for surveying;
•  the resources (instruments & personnel) to be used;
•  the control points / stations to be used ( those already available and/ or to set up).
The planning operation needs a-priori field visit and this is known as reconnaissance.
Field Observation
It involves
•  Collection of field data by making necessary measurements;
•  Recording of observed data in a systematic manner.
Before starting any field observation, the permanent adjustments of all the instruments need to be checked thoroughly by trained personnel and if required, it must be adjusted
  • Office Work
    It involves
    •  Processing, analysing and calculation of observed data;
    •  Preparation of necessary data (for making plan or map of the area);
    •  Making of a plan or map of the area;
    •  Computation of relevant field parameters as per design for setting out engineering works at site.
    Setting out Works
    To locate and establish different parameters / dimensions at the site as per design for further engineering works.

Definition, Importance and types of Surveying

Posted date: 10:37 AM / comment : 0

Definition of Surveying
Surveying is defined as the science of making measurements of the earth specifically the surface of the earth. This is being carried out by finding the spatial location (relative / absolute) of points on or near the surface of the earth.
Different methods and instruments are being used to facilitate the work of surveying.
The primary aims of field surveying are :
•  to measure the Horizontal Distance between points.
•  to measure the Vertical elevation between points.
•  to find out the Relative direction of lines by measuring horizontal angles with reference to any arbitrary direction and
•  to find out Absolute direction by measuring horizontal angles with reference to a fixed direction.
These parameters are utilized to find out the relative or absolute coordinates of a point / location.

Importance of Surveying to Civil Engineers
The planning and design of all Civil Engineering projects such as construction of highways, bridges, tunnels, dams etc are based upon surveying measurements.
Moreover, during execution, project of any magnitude is constructed along the lines and points established by surveying.
Thus, surveying is a basic requirement for all Civil Engineering projects.
Other principal works in which surveying is primarily utilised are
•  to fix the national and state boundaries;
•  to chart coastlines, navigable streams and lakes;
•  to establish control points;
•  to execute hydrographic and oceanographic charting and mapping; and
•  to prepare topographic map of land surface of the earth.

Objectives of Surveying
•  To collect field data;
•  To prepare plan or map of the area surveyed;
•  To analyse and to calculate the field parameters for setting out operation of actual engineering works.
•  To set out field parameters at the site for further engineering works.
Divisions of Surveying
The approximate shape of the earth can best be defined as an oblate tri-axial ovaloid. But, most of the civil engineering works, concern only with a small portion of the earth which seems to be a plane surface. Thus, based upon the consideration of the shape of the earth, surveying is broadly divided into two types.
  • Geodetic Surveying
  • Plane Surveying
Fundamental assumptions in Plane surveying
•  All distances and directions are horizontal;
•  The direction of the plumb line is same at all points within the limits of the survey;
•  All angles (both horizontal and vertical) are plane angles;
•  Elevations are with reference to a datum.
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