建筑工程专业英语unit5.ppt

Lesson 5 Building Engineering Surveying TEXT Surveying is one of the oldest activities of the civil engineering and remains a primary component of civil engineering. It is also one field that continues to undergo phenomenal changes due to technological developments in digital imaging and satellite positioning. These modern surveying tools are not only revolutionizing regular surveying engineering tasks but are also impacting a myriad of applications in a variety of fields[1]. Before any civil engineering project can be designed, a survey of the site must be made. Surveying means measuring and recording the earths surface with the greatest degree of accuracy possible by means of maps. Some engineering projects, for example, highways, dams, or tunnels, may require extensive surveying in order to determine the best and most economical location or route. Modern surveying engineering encompasses several speciality areas. There are two kinds of surveying: plane and geodetic. The most primary area perhaps is plane surveying because it is so widely applied in engineering and surveying practice. In plane surveying, we consider the fundamentals of measuring distance, angle, direction, and elevation. These measured quantities are then used to determine position, slope, area, and volume-the basic parameters of civil engineering design and construction. Plane surveying is the measurement of the earths surface as though it were a flat surface without a curvature. Within areas of about 20 kilometers square-meaning a square, each side of which is 20 kilometers long-the effects of the earths curvature are negligible relative to the positional accuracy[2]. For larger areas, however, a geodetic survey, which takes into account the curvature of the earth, must be made (Fig5.1). The different kinds of measurements in a survey include distances, elevations (heights of features within the area), boundaries (both man-made