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Level Loop

Level Loop
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  • Land Surveyor

    Where is this Luke, and what are the circumstances?

    Keith

  • GEO Ambassador

    Topographic Surveying

    • determining the relative locations of points (places) on the earth's surface by measuring horizontal distances, differences in elevation and directions
    • topos (Gr.): place; topographic maps give the locations of places (observable features); they serve as base maps

    Use of topographic surveying in geography:

    • producing topographic maps
    • constructing topographic (cross-sectional) profiles
    • establishing vertical and horizontal control for accurately defining locations

    General Principles

    1. select a scale in advance; this determines the plotable error

    2. work from the most accurate to the least accurate methods

    3. orient each survey, preferably with respect to true north

    4. the first stage of surveying is always establishing horizontal and vertical control: the distance, direction and difference in elevation between key fixed points

    5. establish a survey plan that includes checks on accuracy, e.g. redundant points, pacing of measured distances, surveying between fixed positions, etc.

     

    Methods

    1. horizontal distance
      • tachymetry: a rapid optical means of measuring distance using a telescope with cross hairs and a stadia rod (one stadium = about 607 feet)
      • measuring slopes distance with a tape and reducing it to horizontal distance using the cosine of the slope gradient
    2. difference in elevation
      • leveling with a level telescope and a stadia rod, or
      • measuring a vertical angles and a slope distance (height is the product of the distance and sine of the angle)

      Leveling is more accurate since elevation differences are measured not calculated. Two readings are taken at each position of the automatic level: a backsight towards a station located before the level on the traverse and a foresight to the next station on the traverse. Thus the stadia rod occupies two stations, before and after the level on the survey.  The difference in elevation between successive stations if the difference between the backsight and the foresight read from the stadia rod.  For each position of the level, the lengths of the foresights and backsights should be approximately the same since accuracy is a function of the distance of a sighting.  The level operator should anticipate the distance to the next station and set up the level midway along this distance (note: the distance that can be sighted decreases with increase in slope, since the stadia rod will disappear above or below the level line of sight).  The lengths of backsight and foresight can be paced by the rod person or measured by the interval between the upper and lower cross hairs (tachymetry).

    3. direction
    • horizontal angle measured with a compass
    • precise measuring devices use vernier scales
    • direction is expressed relative to a reference line or meridian
    • true meridian: a nor
    vertical_control.html
  • Please keep on postin' pictures.. It inspires me. Thank you for the pictures. :)
  • GEO Ambassador
    where is this located exactly? very interesting photo
  • yes it is real, Arnel, I collect this photos.
    I can' remember where I got this one but it is some students running a level loop on a volcanic plain somewhere....
  • Is this real?
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