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….
The basic concept of errors in the data captured by the surveyor may be likened to target shooting. In the first instance, let us assume that a skilled marksman used a rifle with a bent sight, which resulted in his shooting producing a scatter of shots as at A in Figure 2.1. That the marksman…
It should now be apparent that position fixing simply involves the measurement of angles and distance. However, all measurements, no matter how carefully executed, will contain error, and so the true value of a measurement is never known. It follows from this that if the true value is never known, the true error can never…
The system most commonly used for the definition of units of measurement, for example of distance and angle, is the ‘Système Internationale’, abbreviated to SI. The basic units of prime interest are: Length in metres (m) from which we have: Significant Figures Engineers and surveyors communicate a great deal of their professional information using numbers. It…
In surveying nothing is ever absolutely certain. The product of surveying may be thought of as being in two parts, that is, the derivation of the desired quantities such as coordinates of, or distances between, points, and the assessment and management of the uncertainty of those quantities. In other words not only must the survey…