Elem Surveying

Leveling- the process of directly or indirectly measuring vertical distances to determine the elevation of points or their differences in elevations.

Level Surface-is a curved surface which is at any point perpendicular to the direction of gravity or the plumb line.

Level line-is 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-is a plane that is tangent to a level surface at a perpendicular point. It is 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. This line is perpendicular to the direction of gravity at the point of tangency.

Vertical Line – A vertical line at any point is a line parallel to the direction of gravity. It is exemplified by the direction taken by a string supporting a suspended plumb bob passing through a point.

Mean Sea Level – is an imaginary surface of the sea which is midway between high and low tides. It is taken as the reference surface to which most ground elevations are referred.

Datum – is any convenient level surface coincident or parallel with mean sea level to which elevations of a particular area are referred

Elevation – for a particular point, its elevation is the vertical distance above or below mean sea level or any other selected datum.

Difference in Elevation – the difference in elevation between two points is the vertical distance between the two level surfaces in which the points lie.

   Dumpy Level –   is the most widely  used leveling

   instrument

Wye Level –

   has a detachable  telescope which rests in supports called wyes.

   Builder’s level –

   is used primarily

   in the different

   phases of building

   construction where

   a high degree of

   precision is not a

   primary requisite

Automatic Level –

   Self-leveling features

   are incorporated in

   automatic levels.

   It does not use a level vial

   and its ability to level itself

   depends upon the action

   of a complex pendulum-

   and-prism device.    

Tilting Levels –

   it can be tilted or

   rotated about its

   horizontal axis.

Geodetic Levels –

   are employed in first-order leveling work where extreme precision is an important requirement. It is basically another type of tilting level.

Transit as a Level –

   the engineer’s transit has

   always been referred to

   as the “universal

   surveying instrument”

   because of its variety

   of uses.

Laser Level –

   A laser system is separate unit equipped with a portable power supply and may be a helium-neon laser or gas laser.

Hand Level –

   is a hand held instrument used on surveys involving short sights and where a low order of accuracy is sufficient.

Care and Handling
of Instrument

•The level should always be kept in a box when it is not  used.

•It should remain in its carrying case when transported to the work site or when it has to be moved to another distant set up or over rough terrain.

•The level does not have to be detached from the tripod when transferring to another nearby station, provided that it is securely fastened to the tripod and is carried properly.

Differential Leveling- is the process of determining the difference in elevation between two or more points some distance apart.

Benchmark (BM) – a fixed point of reference whose elevation is either known or assumed. They may be permanent or temporary.

Backsight (BS) – reading taken on a rod held on a point of known or assumed elevation. First rod reading taken after the instrument has been set up and leveled.

Foresight (FS) – reading taken on a rod held on a point whose elevation is to be determined. Usually taken in the direction in which the leveling work proceeds.

Backsight Distance (BSD) / Foresight Distance (FSD) – distance from the center of the instrument to the rod on which a backsight/foresight is taken.

Turning Point (TP) – an intervening point between two bench marks upon which a point between two benchmarks 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) –elevation of the line of sight of an instrument above or below a selected reference datum.

•Profile Leveling is the process of determining difference in elevation along a fixed line at designated short measured intervals.

Profile – a curved line which graphically portrays the intersection of a vertical plane with the surface of the earth and the horizontal distances between the points along a surveyed line.

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

Intermediate Foresights – taken along the centerline of the proposed project to provide accurate representation of the ground surface.

Full Stations – points established along the profile level route at uniformly measured distances.

Plus Stations – any intermediate point established along a profile level.  Mostly for location of critical points.

Vertical Exaggeration – drawing the vertical scale for a profile much larger than horoizontal scale to accentuiate differences in elevation.