What is Leveling in Surveying?
The art of determining the relative heights of points on the surface of the earth is termed as “leveling.”
A leveling instrument called “Level” and “Staff” is employed for this purpose along with other equipments which are explained in this article in details.
Definition of Important Terms in Surveying and Levelling.
Level Surface.
This is a surface which is normal to the direction of gravity at all points as indicated by a plumb line. The surface of a still lake may be taken as an example of a level surface.
As the earth is an oblique spheroid, a level surface will not be plane but will be a cursed one. Every point on a level surface is equidistant from the center of the earth.
Level Line.
A line lying throughout on a level surface is a level line. This is normal to the plumb line at all points.
Horizontal Plane.
A horizontal plane through a point is a plane tangential to the level surface at the point. This is normal to the direction of gravity at that point.
Horizontal Line.
Any line lying throughout in a horizontal plane is termed as “horizontal line.”
Vertical Plane.
A vertical plane is any plane containing a vertical line. A vertical line at any point is a line normal to the level surface at that point. A plumb line is an example of a vertical line.
Read Also: Surveying Tapes: Types of Measuring Tape Used in Survey.
Datum Surface.
This is an arbitrary surface with reference to which the elevations of points are measured and compared.
Elevation of a Point.
Elevation of a point is the vertical distance above or below the datum. This is usually called the reduced level (R.L) of the point. This may be positive or negative accordingly as the point is above or below the datum.
Line of Collimation.
The line of collimation or the line of sight is the line joining the intersection of cross-hairs to the optical center of the object glass and its continuation.
Axis of Telescope.
The axis of a telescope is the line joining the optical center of the object glass to the center of the eye piece.
Axis of Bubble Tube.
The axis of bubble tube or level tube is the line tangential to the longitudinal curve of bubble tube at its middle point. This is horizontal when the bubble is centered. This is also called “bubble line.”
Vertical Axis.
The vertical axis is the line about which the telescope can be rotated in a horizontal plane.
