Tiêu đề Lesson 5 Surveying.pdf ✅

DIFFERENTIAL LEVELING Backsight (BS) is a reading taken on a rod held on a point of known or assumed elevation. It is a measure of the vertical distance from the established line of sight to the point sighted, and is always the first rod reading taken after the instrument has been set up and leveled. Backsights are frequently referred to as plus (+) sights since they are added to the elevation of points being sighted to determine the height of instrument. backsight does not necessarily mean that it is always sight taken backward. BM1 Elev. 100 1 BS Bench Mark (BM) is a fixed point of reference whose elevation is either known or assumed. They may be permanent or temporary. Permanent bench marks (PBM) are those which are established at intervals throughout the country by the Philippine Coast and Geodetic Surveys (PCGS) or the Bureau of Lands. They serve as points of reference for levels in a given locality and their elevations are determined by precise leveling methods.
1 Foresight (FS) is a reading taken on a rod held on a point whose elevation is to be determined is called a fore sight. It is represented as a vertical distance from the line of sight of the instrument to the point observed. Since the reading for a foresight is subtracted from the point on which the rod is held, a foresight is usually height of instrument to determine the elevation referred to as a minus (-S) sight. IFS BM1 Elev. 100 BS Sta. 0+060 Sta. 0+100 Sta. 0+120 DIFFERENTIAL LEVELING
1 IFS BM1 Elev. 100 BS Sta. 0+060 Sta. 0+100 Sta. 0+120 Turning Point (TP) is an intervening point between two bench marks upon which point foresight and backsight rod readings are taken to enable a leveling operation to continue from a new instrument position. Height of Instrument (HI) is the elevation of the line of sight of an instrument above or below a selected reference datum. OBSTRUCTION 2 TP1 DIFFERENTIAL LEVELING