SURVEYING LEC

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

  in elevation
• Leveling - undertaken to provide necessary data for engineering design and construction and the production of topographic maps; buildings roads, canals and other vertical and horizontal structures can be designed and laid out by the process of leveling to best conform to the configuration of the ground
• Level Surface - 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 - plane that is tangent to a level surface at a particular point
• Horizontal Line - a straight line in a horizontal plane which is tangent to a level line at one point perpendicular to the direction of gravity at the point of tangency
• Vertical Line - a line parallel to the direction of gravity
• Mean Sea Level - an imaginary surface of the sea which is midway between high and low tides reference surface to which most ground elevations are referred
• Datum - any convenient level surface coincident or parallel with mean sea level to which elevations of a particular area are referred
• Elevation - vertical distance above or below mean sea level or any other selected datum positive or negative depending if the point is above or below mean sea level
• Difference in Elevation - the vertical distance between the two level surfaces in which the two points lie
• Direct or Spirit Leveling - method of determining the elevation of points some distance apart by a series of set ups of a leveling instrument along a selected route; spirit leveling if the device used is a spirit level
• Reciprocal Leveling - process of accurately determining the differences in elevation between two intervisible points located at a considerable distance apart and between which points leveling could not be performed in the usual manner wide river, deep

  ravine, across canyons and across gullies
• Profile 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; used in the design of roads,

  railroads, canals, drainage systems and transmission lines
• Trigonometric Leveling - employs the use of trigonometric equations to determine the difference in elevation between two points from measurement of horizontal or slope distance and the vertical angle between the points
• Stadia Leveling - combines features of

  direct and trigonometric leveling; differences in elevation

  between points are computed from observed vertical angles and the three intercepts on a rod
• Barometric Leveling - determine differences in elevation between points by measuring the variation of atmospheric pressure at each point by means of a barometer; based from the principle that differences in elevation are proportional to the differences in

  atmospheric pressure
• Cross-section Leveling - a representation of the ground surface on either side of the centerline in highway or railroad construction; short profiles at right angles to the line of work are usually plotted at regular intervals.
• Borrow-pit Leveling - method of determining the relative elevations of points in borrow pit excavations for the purpose of calculating volumes of earthwork in the construction of roads and railroads
• Dumpy Level - a long telescope, which fixes the direction of the

  line of sight, is rigidly attached to the level bar which can be rotated through 360 degrees; most widely used direct leveling instrument
• Wye Level - very identical to the dumpy level except in the manner by which their telescopes are attached to the supporting

  level bar; has a detachable telescope which rests in supports called wyes ; now almost obsolete
• Builder's Level - used primarily in the different phases of building

  construction; engineers, architects and builders use it in the setting of concrete forms, batter boards and in establishing

  grades for earthworks; also called construction level

  or an architect’s level
• Automatic Level - with self leveling features and become

  popular for conventional leveling work because of the ease and speed of their operation.
• Tilting Level - can be tilted or rotated about its horizontal axis; a bull’s eye level is employed for its quick and approximate

  leveling; equipped with a horizontal circle which makes it suitable

  for layout and construction surveys.
• Geodetic Level - another type of tilting level; employed in first order leveling work where extreme precision is an important

  requirement; equipped with stadia hairs in addition to the standard vertical and horizontal cross hairs to make it suitable for

  three wire leveling
• Transit as a Level - the engineer’s transit has always been referred to as the “universal surveying instrument” because of

  its variety of uses; no doubt it can be used for leveling

  work; provide results which are fairly precise but not as good as those obtained with conventional levels because of relatively shorter telescope and level vial
• Laser Level - new innovation introduced to surveying operations is the use of lasers; laser system is a separate unit equipped with a portable power supply; mounted or attached to conventional surveying instrument such as levels, transits and theodolites
• Hand Level - hand held level instrument used on surveys involving short sights and where a low order of accuracy is sufficient; useful in reconnaissance surveys, in cross sectioning, and in taping to determine if the tape is held horizontally during measurement
• Leveling Rod - a graduated rod which is used for measuring the vertical distance between the line of sight through a leveling instrument and the point whose elevation is either required or known; made of wood, fiberglass or metal with graduations in meters and decimals which start from 0 at the bottom and extending upwards to lengths of 3 to 4 meters
• Self-reading rod - most commonly used type of leveling rod; can be read directly by the instrumentman through the telescope

  by noting the apparent intersection of the horizontal hair on the rod
• Target rod - can be read directly by the instrumentman

  through the telescope by noting the apparent intersection

  of the horizontal hair on the rod
• Rods named after cities or states - Philadelphia, Detroit,

  Chicago, Florida, Boston, New York, Troy and San Francisco; Philadelphia is the commonly used type of rod; a combination of self reading and target rod
• Rod Ribbons - graduations are marked either on canvass or metal strips attached to a long piece of lumber by staples; can be easily removed from the wood to which it is attached, rolled and put into one’s pocket
• Precise rod - form of rod ribbon which uses a graduated invar

  strip permanently fastened to a 4 meter long wooden or metal frame; equipped with rod level
• Geodetic rod - similar to precise rod except that a nilvar metal strip is used instead of invar; nilvar is an alloy of metal with

  a very low coefficient of linear expansion; graduations are painted

  upside down for use with inverting telescopes
• Tape rod - also known as automatic rod but seldomly used but

  advantageous when numerous elevations are to be determined

  from a single set up of the leveling instrument; useful in profile leveling, taking cross sections and for the different phases involved in building construction and layout
• Rod Level - device used for fast and correct

  plumbing of a leveling rod; L shape in design and consists of a

  small circular spirit level fastened to the rod or to a small bracket

  held against the side of the rod; when bull’s eye bubble is

  centered, the rod is plumb or correctly held vertical
• Target - small device attached to the rod when extremely long sights make direct reading of the rod difficult or impossible;

  made of metal and may be circular, elliptical or rectangular in shape; alternating red and white quadrant painted on its face; has a rectangular opening in the front to expose a portion of the rod in order that readings can be made; also used when rod is held in poorly lighted places, atmospheric conditions may cause adverse effects on reading a rod accurately
• Telescope - a metal tube containing a system of lenses used to fix the direction of the line of sight and in magnifying the apparent size of objects in the field of view;
• Telescope - invented by Jan Lippershey (a Dutchman) in 1608; Johannes Kepler (a mathematician) was the one who suggested how the telescope could be employed for use in surveying instruments; developed the Keplerian or astronomical telescope consisting of a tube with variable length which has an

  objective lens, cross wires and an eyepiece