Guide To Learn
The theodolite is the most accurate instrument used mainly for measuring horizontal and vertical angles. It can also be used for locating points on a line, prolonging survey lines, finding the differences in elevations, setting out grades, ranging curves, etc. Depending upon the facilities provided for the reading of observations, the theodolites may be classified […]
This method consists in determining the difference of level between consecutive points by comparing each point, after the first, with that immediately preceding it. The difference between their staff readings indicates rise or fall depending on whether the staff reading at the point is smaller or greater than that at the preceding point. The reduced […]
In this method, the reduced levels of points are computed by calculating the reduced levels of the plane of collimation for each set up of the instrument. The height of collimation is obtained by adding the staff reading, which must be back sight to the known reduced level of the point on which the staff […]
A map represents the relative positions of points in a plan. The value of the map is enhanced if the variation in the elevation of the earth’s surface is also included along with their relative position in a plan. There are two methods by which the conformation of the ground may be presented on a […]
Fly levelling is a process of finding the level difference between two points and the levelling consists of taking back sights and fore sights only and not intermediate sights. Differential levelling is the determination of level difference between two points; check levelling is finding the level difference between points in a way of checking the […]
The survey work is mainly divided into two: (1) field work and (2) office work. In the field, necessary adjustments are done and the results are recorded in a systematic manner as explained below. 27.5.1 Adjustments of a level A level needs two type of adjustments, i.e., 27.5.1.1 Temporary adjustments The adjustments which are made […]
There are four kinds of bench marks. Figure 27.10 Figure showing a permanent bench mark Great trigonometric bench marks (GTS) are established by the Survey of India Department. They will be marked with very high accuracy at intervals, all over the country by this department. Their positions and elevations above the standard datum […]
A straight rectangular wooden rod graduated in metres/feet and further smaller divisions is called a levelling staff. The bottom of the levelling staff represents the zero reading. The reading given by the line of sight on a levelling staff held vertically is the height of the line of collimation above the point on which the […]
The level furnishes a horizontal line of sight. The level consists of the following main parts. 27.2.1 Telescope Telescope is an optical instrument for magnifying and viewing the images of distant objects. The telescope of a levelling instrument is a metallic tube having an eyepiece at one end and an object glass at the other […]
The instruments used in levelling are as follows: