MEASUREMENT OF VERTICAL DISTANCE Flashcards
(30 cards)
is the general term applied to any of the various processes by which elevations of points or differences in elevation are determined. It is a vital operation in producing necessary data for mapping, engineering design, and construction.
Leveling
A line that follows the local direction of gravity as indicated by a plumb line.
Vertical Line
A curved surface that at every point is perpendicular to the local plumb line (the direction in which gravity acts).
Level Surface
A line in a level surface - therefore, a curved line.
Level line
A plane perpendicular to the local direction of gravity. In plane surveying, it is a plane perpendicular to the local vertical line.
Horizontal Plane
A line in a horizontal plane. In plane surveying, it is a line perpendicular to the local vertical.
Horizontal line
Any level surface to which elevations are referred. This is the surface that is arbitrarily assigned an elevation of zero. This level surface is also known as a reference datum
Vertical datum
It is the vertical distance of a point above or below an arbitrarily assumed level surface or curved surface.
Elevation
It is the vertical distance between the two level surfaces in which the points lie.
Difference in Elevation (DE)
A relatively permanent object, natural or artificial, having a marked point whose elevation above or below a reference datum is known or assumed. Common examples are metal disks set in concrete, reference marks chiselled on large rocks, non-movable parts of fire hydrants, curbs, etc.
Bench Marks (BM)
An intervening point between two bench marks upon which point foresight and backsight rod readings are taken
Turning Point (TP)
A rod reading taken on a point of known elevation (BM or TP). It is usually called a plus sight.
Backsight (B.S.)
The horizontal distance from level to rod on a B.S.
Backsight Distance (BSD)
A rod reading taken on a point of unknown elevation (BM or TP to be established). It is usually called a minus sight.
Foresight (F.S.)
The horizontal distance from level to rod on a F.S.
Foresight Distance (FSD)
The elevation of the line of sight of the telescope above the datum when the instrument is leveled.
Height of Instrument (H.I.)
TYPES OF LEVELS
Dumpy Level
Automatic Level
Tilting Level
Laser Level
Digital Level
Hand Level
▪ general purpose instrument and commonly referred to as engineer’s level
▪ Provides excellent introduction to levels in general though has been superseded by self leveling instruments
Dumpy Level
▪ a.k.a. self-leveling level
▪ like dumpy level it is also regarded as engineer’s level
▪ leveled by the use of a circular spirit or bull’s eye level and the compensator maintains a horizontal line of sight
▪ advantages: light, easy to handle and operation is quick and accurate
Automatic Level
▪ can be tilted or rotated about its horizontal axis. ▪ has a level bubble with a sensitivity of 10” per 2 mm division and the images of the bubble ends are viewed through the eyepiece
▪ equipped with coincidence bubbles used for precise leveling
Tilting Level
▪ used commonly in construction works to maintain the elevations needed
▪ saves time and effort since it can detect the prism in a whole revolution of 360𝑜
▪ advantage for layout work in construction since it is simple, one button operation and fully automatic general construction
Laser Level
Easy
▪ Aims the telescope at the staff, adjust focus and press a single key and it measures height and distance simultaneously
Fast
▪ measurement is completed in < 3 sec.
Accurate
▪ automatic operation eliminates conventional error by the operator.
Digital Level
▪ Widely used for rough leveling
▪ Consists of a metal sighting tube about 6 in long on which is mounted a level vial
Hand Level
▪ are graduated wooden rods of rectangular section by means of which difference in elevation is measured
▪ some are also in aluminum alloy and fiberglass
▪ lower ground end (usually the point of zero measurement) is shod with metal to protect it from wear
Leveling Rods
