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# Note for Surveying-1 - s-1 by Naresh Sankuru

• Surveying-1 - s-1
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Naresh Sankuru
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UNIT 2 TACHEOMETRIC SURVEYING Tacheometric Surveying Structure 2.1 Introduction Objectives 2.2 Principles of Tacheometry 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.2.6 2.2.7 2.3 Advantages of Tacheometry Tacheometer Stadia Rods Systems of Tacheometric Measurements Basic Principle of Stadia Method Movable Hair Method Anallactic Lens Methods of Tacheometry 2.3.1 Various Cases – Inclined Sights with Staff Vertical and Staff Normal to the Line of Sight 2.3.2 Tangential Method 2.3.3 Subtense Bar Method 2.3.4 Tacheometric Traversing 2.4 Summary 2.5 Answers to SAQs 2.1 INTRODUCTION Generally, horizontal distances are measured by direct methods, i.e. laying of chains or tapes on ground. These methods are not always convenient if the ground is undulating, rough, difficult and inaccessible. Under these circumstances, indirect methods are used to obtain distances. One such method is “Tacheometry”. Using tacheometric methods, elevations can also be determined. It is in fact a branch of angular surveying in which both the horizontal and vertical positions of points are determined from the instrumental observations, the chain surveys being entirely eliminated. Objectives After studying this unit, you should be able to • explain the principle of tacheometry, • describe various tacheometric methods, • learn stadia principles, • learn fixed hair and movable hair methods, and • carry out tacheometrical surveying. You will also be learning principles of anallactic lens which makes the calculations simple. Staff vertical and staff normal cases are also discussed. You will also understand tangential tacheometry and subtense bar methods including tacheometrical traversing. 37