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CHAPTER 11

ELEMENTS OF SURVEYING AND SURVEYING EQUIPMENT

This chapter provides an overview of surveying in general with emphasis on the principles and procedures of basic surveying and the use of various surveying equipments, instruments, and accessories. As an EA, you should realize that accuracy in surveying is essential because other factors affecting sound decisions in engineering practice are dependent upon the results of your survey.

Surveying is a science that deals with the determination of the relative positions of points on or near the earth’s surface. These points may be needed to locate or lay out roads, airfields, and structures of all kinds; they may be needed for cultural, hydrographic, or terrain features for mapping; and, in the military, these points may be targets for artillery and mortar fires. The relative horizontal positions of these points are determined from distances and directions measured in the field, while their vertical positions are computed from the differences in elevations, which are measured directly or indirectly from an established point of reference or datum.

The earliest applications of surveying were for the purpose of establishing the boundaries of land. Although many surveyors are still preoccupied with establishing or subdividing boundaries of landed properties, the purposes of surveys have branched out to many areas that parallel the advancement of various engineering fields and other areas of civilization. Surveyors may be called upon in court to substantiate definite locations of various objects, such as those involving major traffic accidents, maritime disasters, or even murder cases, in which direction and distance have a bearing.

Surveying continues to play an extremely important role in many branches of engineering. The results of today’s surveys are being used to map the earth above and below; for navigational charts for use in the air, on land, and at sea; and for other major survey operations for related tasks in geology, forestry, archeology, and landscape architecture. As a surveyor in the Naval Construction Force, you will be required to submit survey results before, during, and after planning and construction of advanced base structures, bridges, roads, drainage works, pipelines, and other types of conventional ground systems. In addition, an EA assigned to an oceanographic unit may be involved in hydrography to a great extent, establishing an offshore triangulation network, depth sounding, and mapping.

Again, though these surveys are for various purposes, still the basic operations are the same— they involve measurements and computations or, basically, fieldwork and office work.

CLASSIFICATION OF SURVEYING 

Generally, surveying is divided into two major categories: plane and geodetic surveying.

PLANE SURVEYING

PLANE SURVEYING is a process of surveying in which the portion of the earth being surveyed is considered a plane. The term is used to designate survey work in which the distances or areas involved are small enough that the curvature of the earth can be disregarded without significant error. In general, the term of limited extent. For small areas, precise results may be obtained with plane surveying methods, but the accuracy and precision of such results will decrease as the area surveyed increases in size. To make computations in plane surveying, you will use formulas of plane trigonometry, algebra, and analytical geometry.

A great number of surveys are of the plane surveying type. Surveys for the location and construction of highways and roads, canals, landing fields, and railroads are classified under plane surveying. When it is realized that an arc of 10 mi is only 0.04 greater that its subtended chord; that a plane surface tangent to the spherical arc has departed only about 8 in. at 1 mi from the point of tangency; and that the sum of the angles of a spherical triangle is only 1 sec greater than the sum of the angles of a plane triangle for a triangle having an area of approximately 75 sq mi on the earth’s surface, it is just reasonable that the errors caused by the earth’s curvature be considered only in precise surveys of large areas.



 


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