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Levelling - Definition
Unit 1- Surveying
Levelling
Definition
Definition
Levelling is the branch of surveying the object of which is
- To find the elevation of given points with respect to a given or assumed datum.
- To establish points at a given elevation or at different elevations with respect to given or assumed datum. Levelling deals with measurement in a vertical plane.
Level Surface
A level surface is defined as a curved surface at which each point is perpendicular to the direction of gravity at the point. The surface of still water is truly level surface.
Level Line
A level line is a line lying on a level surface. It is normal to the plumb line at all points.
Horizontal Plane
Horizontal plane through a point is a plane tangential to the level surface at that point. It is perpendicular to the plumb line through the point.
Horizontal Line
It is a straight line tangential to the level line at a point. It is perpendicular to the plumb line.
Vertical Line
It is a line normal to the level line at a point. It is commonly considered to be the line defined by a plumb line.
Datum
Datum is any surface to which elevations are referred. The mean sea level offords a convenient datum world over and elevations are commonly given as so much above or below sea level.
Elevation
The elevation of a point on or near the surface of the earth is its vertical distance above or below an arbitrarily assumed level surface or datum. The difference in the elevation between two points is the vertical distance between the two level surfaces in which the two points lie.
Vertical Angle
Vertical angle is an angle between two intersecting lines is a vertical plane.
Mean Sea Level
Mean sea level is the average height of the sea for all stages of the tides. At any particular place it is derived by averaging the hourly tide heights over a long period of 19 years.
Bench Mark
Bench mark is a relatively permanent point of reference whole elevation with respect to some assumed datum is known. It is used either as a starting point for leveling or as a point upon which to close as a check.
A level surface is defined as a curved surface at which each point is perpendicular to the direction of gravity at the point. The surface of still water is truly level surface.
Level Line
A level line is a line lying on a level surface. It is normal to the plumb line at all points.
Horizontal Plane
Horizontal plane through a point is a plane tangential to the level surface at that point. It is perpendicular to the plumb line through the point.
Horizontal Line
It is a straight line tangential to the level line at a point. It is perpendicular to the plumb line.
Vertical Line
It is a line normal to the level line at a point. It is commonly considered to be the line defined by a plumb line.
Datum
Datum is any surface to which elevations are referred. The mean sea level offords a convenient datum world over and elevations are commonly given as so much above or below sea level.
Elevation
The elevation of a point on or near the surface of the earth is its vertical distance above or below an arbitrarily assumed level surface or datum. The difference in the elevation between two points is the vertical distance between the two level surfaces in which the two points lie.
Vertical Angle
Vertical angle is an angle between two intersecting lines is a vertical plane.
Mean Sea Level
Mean sea level is the average height of the sea for all stages of the tides. At any particular place it is derived by averaging the hourly tide heights over a long period of 19 years.
Bench Mark
Bench mark is a relatively permanent point of reference whole elevation with respect to some assumed datum is known. It is used either as a starting point for leveling or as a point upon which to close as a check.
Last modified: Thursday, 12 May 2011, 5:50 AM