SURVEYING II (FOR IV – SEMESTER) UNIT I = TACHEOMETRIC SURVEYING UNIT II = CONTROL SURVEYING UNIT III = SURVEY ADJUSTMENTS UNIT IV = ASTRONOMICAL SURVEYING UNIT V = HYDROGRAPHIC AND ADVANCE SURVEYING PREPARED BY A.SENTHIL KUMAR,M.E ASST.PROF/CE
DEPARTMENT OF CIVIL ENGINEERING UNIT – 2 CONTROL SURVEYING Working from whole to part - Horizontal and vertical control methods - Triangulation - Signals - Base line - Instruments and accessores - Corrections - Satellite station - Reduction to centre - Trignometric levelling - Single and reciprocal observations - Modern trends – Bench marking Two Mark Questions and Answers 1. What is trignometric levelling? Trignometrical levelling is the process of determining the differences of elevations of stations from observed vertical angles and known distances, which are assumed to be either horizontal or geodetic lengths at mean sea level. The vertical angles may be measured by means of an accurate theodolite and the horizontal distances may either be measured (in the case of plane surveying) or computed (in the case of geodetic observations). 2. Define geodetic surveying The object of the geodetic surveying is to determine very precisely the relative or absolute positions on the earth’s surface of a system of widely separated points. The relative positions are determined in terms of the lengths and azimuths of the lines joining them. The absolute positions are determined in terms of latitude, longitude, and elevation above mean sea level. However, the distinction between geodetic surveying and Plane surveying is fundamentally one of extent of area rather than of operations. 3. What is triangulation? In triangulation, the system consists of a number of inter-connected triangles in which the length of only one line, called the base line, and the angles of the
triangles are measured very precisely. Knowing the length of one side and the three angles, the lengths of the other two sides of each triangle can be computed. 4. What are the disadvantages of using triangulation? The defect of triangulation is that it tends to accumulate errors of length and azimuth, since the length and azimuth of each line is based on the length and azimuth of the preceding line. To control the accumulation of errors, subsidiary bases are also selected. At certain stations, astronomical observations for azimuth and longitude are also made. These stations are called Laplace Stations. 5. What are the objects of Geodetic Triangulation? (1) To provide the most accurate system of horizontal control points on which the less precise triangles may be based, which in turn may form a framework to which cadastral, topographical, hydrographical, engineering and other surveys may be referred. (2) To assist in the determination of the size and shape of the earth by making observations for latitude, longitude and gravity.
- Spring '20
- Celestial coordinate system, great circle, base line