Surv 3

• LEVELING

  • General term applied to any of the various processes by which

  elevations of points or differences in elevation are determined

  • Vital operation in producing necessary data for mapping,

  engineering, design and construction.
• VERTICAL LINE

  • A line that follows the local

  direction of gravity indicated by

  a plumb line.
• LEVEL SURFACE

  • Curved surface that every point

  is perpendicular to the local

  plumb line

  • Approximately spheroidal in

  shape
• LEVEL LINE

  • A line in a level surface –

  therefore a curved line.
• HORIZONTAL PLANE

  • Plane perpendicular to the local

  direction of gravity

  • Plane perpendicular to the local

  vertical line (in plane surveying)
• HORIZONTAL LINE

  • A line in a horizontal plane.

  • A line perpendicular to the local

  vertical (in plane surveying)
• VERTICAL DATUM

  • Level surface to which elevations

  are references.

  • Surface arbitrarily assigned an

  elevation of zero

  • Also known as reference datum

  since points using this datum have

  heights relative to this surface
• ELEVATION

  • Distance measured along a

  vertical line from a vertical

  datum to a point or object
• GEOID

  • Particular level surface that

  serves as a datum for all

  elevations and astronomical

  observations

  • Imaginary sea level that has a

  wavy surface all over the Earth.
• MEAN SEA LEVEL

  • Average height for the surface

  of the seas for all stages of tide

  over a 19-year period as

  defined by National Geodetic

  Vertical Datum of 1929, usually

  taken at hourly intervals, at 26

  gaging stations along the

  Atlantic and Pacific Ocean and

  the Gulf of Mexico.
• TIDAL DATUM

  • Vertical datum used in coastal

  areas for establishing property

  boundaries of lands bordering

  waters subject to tides

  • Provides the basis for location

  fishing and oil drilling rights in

  tidal waters, and the limits of

  swamp and overflowed lands.
• BENCHMARK (BM)

  • Relatively permanent object,

  natural or artificial, having a

  marked point whose elevation

  above or below a reference

  datum is known or assumed.

  • Definite point on an object of

  known elevation which serves

  as reference for levelling work.
• VERTICAL CONTROL

  • Series of benchmarks or other

  points of known elevation

  established throughout an area

  • Also termed as basic control or

  level control
• DIRECT OR SPIRIT LEVELLING

  • Most precise method of determining elevations and is the one

  commonly used

  • It is done by measuring vertical distances directly
• INDIRECT OR TRIGONOMETRIC LEVELLING

  • It is done by measuring vertical angles and horizontal or slope

  distances
• RECIPROCAL LEVELLING

  • Process of accurately

  determining the difference in

  elevation between two

  intervisible points located at a

  considerable distance apart

  and between which points

  levelling could not be

  performed in the usual

  manner.
• PROFILE LEVELLING

  • Determining 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
• STADIA LEVELLING

  • Combines features of direct levelling with those of trigonometric

  levelling
• BAROMETRIC LEVELLING

  • Involves 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 LEVELLING

  • In highway construction, it is often necessary to obtain a

  representation of the ground surface on either side of the

  centerline
• BORROW PIT LEVELLING

  • It is a method of determining the relative elevations of points in

  borrow pit excavation for the purpose of calculating volumes of

  earthwork.
• METHODS OF LEVELLING

  DIRECT OR SPIRIT LEVELLING

  INDIRECT OR TRIGONOMETRIC LEVELLING

  RECIPROCAL LEVELLING

  PROFILE LEVELLING

  STADIA LEVELLING

  BAROMETRIC LEVELLING

  CROSS-SECTION LEVELLING

  BORROW PIT LEVELLING
• INSTRUMENTAL ERROR

  • Line of Sight

  • Cross hair not exactly

  horizontal

  • Rod not correct

  length

  • Tripods legs loose
• PERSONAL ERROR

  • Bubble not centered

  • Parallax

  • Faulty Rod Reading

  • Rod Handling

  • Target Setting
• NATURAL ERROR

  • Curvature of the

  Earth

  • Refraction

  • Temperature

  Variation

  • Wind

  • Settlement of the

  Instrument

  • Settlement of a

  turning point
• BENCHMARK (BM)

  • Definite point on an object, the

  elevation and location of which

  are known
• TURNING POINT (TP)

  • Intervening point between two

  bench marks upon which point

  foresight and backsight rod

  readings are taken
• BACKSIGHT (BS)

  • Rod reading taken on a point of

  known elevation; sometimes

  called a plus sight
• FORESIGHT (FS)

  • Rod reading taken on a point

  the elevation of which to be

  determined; sometimes called a

  minus sight
• HEIGHT OF INSTRUMENT (HI)

  • Elevation of the line of sight of

  the telescope above the datum

  when the instrument is leveled.