Disadvantage of chain surveying is that, in it only distances are measured and hence area is to be covered with a network of triangles. If the length as well as angle of a line can be measured with respect to a known direction then it is possible to plot a line, independent of length of other lines. Hence, in such cases there is no compulsion of going for a network of triangles only. Compass is an instrument which can be used to measure the direction of a survey line with respect to magnetic north-south. The magnetic north-south direction which is the reference direction is called meridian (reference direction) and the angle between the line and the meridian is called bearing. Use of compass for measuring direction of a line simplities the surveying to a great extent.
In this chapter construction of different types of compasses, the system of noting bearings of the lines, some problems associated with measurement with compass are explained and then field work involved in compass survey is presented.
â€”â€“13.1Â Types of Compass
â€”â€“13.2Â Method of Using a Compass
â€”â€“13.4Â Whole Circle Bearing and Reduced Bearing
â€”â€“13.5Â Computation of Angles
â€”â€“13.6Â Declination and DIP
â€”â€“13.7Â Local Attraction
â€”â€“13.8Â Chain and Compass Surveying Field Work