The earth is an oblate spheroid, length of equatorial axis being 12756.75 km and polar axis being 12713.80 km. Since the difference between these two axes and irregularities on the earth surface are very small (Note. Height of Mount Everest is 8.79 km) compared to these two axes, the earth may be treated as a…
As stated in the definition, object of surveying is to show relative positions of various objects of an area on paper and produce plan or map of that area. Various uses of surveying are listed below: (i) Plans prepared to record property lines of private, public and government lands help in avoiding unnecessary controversies. (ii)…
Surveying is the art of making measurements of objects on, above or beneath the ground to show theirrelative positions on paper. The relative position required is either horizontal, or vertical, or both.Less precisely the term Surveying is used to the measurement of objects in their horizontal positions. Measurements to deteremine their relative vertical positions is known as levelling.
Although there are many EDM instruments available, there are basically only two methods of measurement employed, namely the pulse method and the more popular phase difference method. Pulse method A short, intensive pulse of radiation is transmitted to a reflector target, which immediately transmits it back, along a parallel path, to the receiver. The measured…
Introduction This chapter is designed to introduce you to the various surveying techniques used to obtain the original field data on which such maps are based. An understanding of these surveying techniques not only provides us with some very useful field mapping tools but it also can give us further insight into the nature of…
To eliminate or minimize the systematic errors of taping, it is necessary to adjust each measured bay to its final horizontal equivalent as follows. Standardization During a period of use, a tape will gradually alter in length for a variety of reasons. The amount of change can be found by having the tape standardized at…
Distance is one of the fundamental measurements in surveying. Although frequently measured as a spatial distance (sloping distance) in three-dimensional space, usually it is the horizontal component which is required. Distance is required in many instances, e.g. to give scale to a network of control points, to fix the position of topographic detail by offsets…
The equipment used in the levelling process comprises optical levels and graduated staffs. Basically, the optical level consists of a telescope fitted with a spirit bubble or automatic compensator to ensure long horizontal sights onto the vertically held graduated staff (Figure 3.8). Levelling staff Levelling staffs are made of wood, metal or glass fibre and…
In order to make OD accessible to all users throughout the country, a series of permanent marks were established, called bench marks. The height of these marks relative to OD has been established by differential levelling and until about 1970 was regularly checked for any change in elevation. (1) Cut bench marks The cut bench…
INTRODUCTION This chapter describes the various heighting procedures used to obtain the elevation of points of interest above or below a reference datum. The most commonly used reference datum is mean sea level (MSL). There is no such thing as a common global MSL, as it varies from place to place depending on local conditions….