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Details about leveling in surveying

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Levelling (or Leveling) is the parts and parcels of surveying and it is conducted on the following purposes :-

i) To determine the elevations of specified points on the basis of a prearranged or hypothetical datum.

ii) To set up points at a prearranged or hypothetical datum. The first point is essential to allow the works for being designed whereas the second point is essential in arranging all types of engineering works. Leveling takes care of measurements in a vertical plane.

Level surface: A level surface means a curved surface that is perpendicular at each point to the direction of gravity at the point. The surface of a still water is a perfectly level surface. Any surface corresponding to the mean spheroidal surface of the earth is, therefore, called as level surface.

Level line: A level line stands for a line that rests in a level surface. So, it is normal to the plumb line at all points.

Horizontal plane: Horizontal plane through a point belongs to a plane that is tangential to the level surface at that point. So, It is perpendicular to the plumb line through the point.

Horizontal line: It belongs to a straight line tangential to the level line at a point. It is situated at a 90 degree angle to the plumb line.

Vertical line: It is a line normal to the level line at a point. It is generally treated as the line demarcated with a plumb line.

Datum: Datum belongs to any surface to which elevation are assigned. The mean sea level provides a smooth datum world over, and elevations are generally provided on over or underneath sea level. It is often more uncomplicated, however, to guess some other datum, specifically, if only the relevant elevation of points are necessary.

Elevation: The elevation of a point on or adjacent to the surface of the earth belongs to its vertical distance over or underneath a randomly accepted level surface or datum. The variation in elevation between two points belong to the vertical distance amid the two level surface in which the two points rest.

Vertical angle: Vertical angle refers to an angle among two bisecting lines in a vertical plane. Normally, one of these lines is horizontal.

Mean sea level: It belongs to the average height of the sea for all phases of the tides. At any specific place it is originated by averaging the hourly tide heights over a long period of 19 years.

Bench Mark: It is a comparatively permanent point of reference whose elevation relating to some assumed datum is recognized. It is employed either as a starting point for levelling or as a point upon which to close as a check.

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Details about leveling in surveying