Measurement of Vertical Distances and Leveling Methods

Vocabulary flashcards generated from the lecture notes on vertical distance measurements, leveling definitions, leveling methods, differential leveling terms, and profile leveling concepts.

Leveling

The process of directly or indirectly measuring vertical distances to determine the elevation of points or differences in elevation.

Level Surface

A curved surface which is at any point perpendicular to the direction of gravity or the plumb line, best represented by the surface of a large body of still water.

Level Line

A curved line in a level surface all points of which are normal to the direction of gravity and equidistant from the center of the earth.

Horizontal Surface

A plane that is tangent to a level surface at a particular point and also perpendicular to the plumb line at the same point.

Horizontal Line

A straight line in a horizontal plane which is tangent to a level line at one point and perpendicular to the direction of gravity at the point of tangency.

Vertical Line

A line parallel to the direction of gravity at any point, exemplified by the direction taken by a string supporting a suspended plumb bob passing through a point.

Mean Sea Level

An imaginary surface of the sea which is midway between high and low tides, taken as the reference surface to which most ground elevations are referred.

Datum

Any convenient level surface coincident or parallel with the mean sea level to which elevations of a particular area are referred.

Elevations

The vertical distance above or below the mean sea level or any other selected datum.

Difference in Elevation

The vertical distance between the two level surfaces in which two points lie.

Direct Leveling

A commonly employed method of determining the elevation of points some distance apart by a series of set ups of a leveling instrument along a selected route.

Reciprocal Leveling

The process of accurately determining the difference in elevation between two intervisible points located at a considerable distance apart between which leveling cannot be performed in the usual manner.

Profile Leveling

A method of leveling used to determine differences in elevation between points at designated short measured intervals along an established line to provide data from which a vertical section of the ground surface can be plotted.

Trigonometric Leveling

A method of leveling employed in determining by trigonometric computations the difference in elevation between two points from measurements of its horizontal or slope distance and the vertical angle between the points.

Stadia Leveling

A form of trigonometric leveling that combines features of indirect leveling with trigonometric leveling to provide reasonable accuracy for preliminary surveys, mapping, and rough leveling.

Barometric Leveling

A leveling method involving the determination of differences in elevation between points by measuring the variation in atmospheric pressure at each point by means of a barometer.

Cross-Section Leveling

A leveling method used in highway or railroad construction where short profiles at right angles to the line of work are plotted at regular intervals to obtain a representation of the ground surface on either side of the centerline.

Borrow-Pit Leveling

A method of determining the relative elevations of points in borrow-pit excavations for the purpose of calculating volumes of earthwork.

Differential Leveling

The process of determining the difference in elevation between two or more points some distance apart requiring a series of set ups of the instrument along a general route.

Bench Mark (BM)

A fixed point of reference whose elevation is either known or assumed, which may be permanent or temporary.

Permanent Bench Marks (PBM)

Bench marks established at intervals throughout the country by the Philippine Coast and Geodetic Surveys (PCGS) or the Bureau of Lands whose elevations are determined by precise leveling methods.

Backsight (BS)

A reading taken on a rod held on a point of known elevation, which is added to the elevation of the point to determine the height of instrument; also referred to as a plus (+S) sight.

Foresight (FS)

A reading taken on a rod held on a point whose elevation is to be determined, which is subtracted from the height of instrument; also referred to as a minus (-S) sight.

Turning Point (TP)

An intervening point between two benchmarks upon which both foresight and backsight rod readings are taken to enable a leveling operation to continue from a new instrument position; also referred to as a change point (CP).

Height of Instruments (HI)

The elevation of the line of sight of an instrument above or below a selected reference datum, also known as height of collimation, determined by adding the backsight reading to the elevation of the point sighted.

Profile

A curved line which graphically portrays the intersection of a vertical plane with the surface of the earth, depicting ground elevations of selected critical points and horizontal distances between them.

Stationing

A numerical designation given in terms of horizontal distance to any point along a profile line that is away from the starting point.

Full Stations

Points established along the profile level route at uniformly measured distances, usually in multiples of $100$, $50$, $30$, $20$, or $10\,\text{meters}$.

Plus Stations

Intermediate points established along a profile level route at breaks in the ground surface slope and at critical points such as culverts, bridges, and other structures.

Intermediate Foresight (IFS)

Ground rod readings taken along the centerline of a proposed project at regular intervals and at points where sudden changes in elevation occur to provide an accurate representation of the ground surface.

Profile Paper

A special heavy grade graphing paper with green, blue, or orange lines spaced accordingly to represent horizontal and vertical scales used for plotting profiles.