MD : ATIKUL ISLAM JUNIOR INSTRACTOR DEPT. OF. CIVIL SUB: surveying3 SUB CODE : 6452 MOB:

Definition of GEODETIC SURVEY a survey of a large land area in which corrections are made for the curvature of the earth's surface or Geodetic surveying is the survey in which the curvature of the earth is taken into account and higher degree of accuracy in linear and angular observations is achieved. The geodetic surveys extend over large areas and lines connecting any two points on the surface of the earth are treated as arcs. For calculating

their projected distances on the plans or maps, the correction for the earth’s curvature is applied to the measured distances. The angles between the curved lines are treated as spherical angles. A knowledge of spherical trigonometry is necessary for making measurements for the geodetic surveys. Reciprocal Leveling This type of surveying is required to obtain the difference in levels between two points which are separated by obstacles.

Triangulation In this type of surveying a network of well defined triangles are formed on the plot of land to be surveyed. Only one line known as base line and all other angles are measured very carefully

Grid iron system

Base net it is the figured formed during a process to magnify the length of a short base line to make it compatible with much longer lines of triangulation networks. Base Net usually form a rhombus, in which short diagonal serves as the base line and long diagonal serves as the base side of the triangulation.

Selection of station point 1. Maintains the integrity of the NT Geodetic Survey System (NTGESS) and Geospatial Reference System, which has a framework based on the Geocentric Datum of Austra. 2. Enables effective and efficient access to the co- ordinated survey control points stored in NTGESS. 3. Provides a survey - accurate geospatial referencing system for the NT Land Information System (NTLIS) and the surveying and mapping industry throughout the Territory; 4. Enhances the cadastral framework and subsequent spatial databases by co-ordination; and

Double chain of triangle Single chain of triangle

5. Offers professional geodetic advice and support to Government, industry and the public on spatial data issues such as: 6. Adoption of the Geocentric Datum of Australia (GDA) for the survey, mapping, LIS and GIS community. 7. Standards and specifications for geodetic data capture, manipulation, storage and dissemination. 8. Use of GPS technology for spatial data capture.

Objectives of triangulation: The main objective of triangulation is to provide a number of stations whose relative and absolute positions, horizontal as well as vertical, are accurately established. More detailed survey is then carried out from these stations.Further objectives are given below 1. To establish accurate control for plane and geodetic survey of large areas. 2. To establish accurate control for photogrammetric survey. 3. To determine accurate locations of points in engineering works.

Classification of Triangulation System: Based on the extent and purpose of the survey, and consequently on the degree of accuracy desired, triangulation survey is classified as First order (primary) Second order (secondary) Third order (tertiary )

First order It is used to determine the shape and the size of the earth or cover vast area like whole country with control points. Second order It is used to cover areas of a region, small country, province. It Consists of network within the first order. Third order It serves the purpose of furnishing the immediate control of detailed engineering and location survey.