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Shvoong Home>Books>Reference>Plane Table Surveying : Civil Engineering Review

Plane Table Surveying : Civil Engineering

Academic Paper Review   by:Tauheed    
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 PLANE TABLE SURVEYING:
      Plane table surveying also called plane tabling, is a method of surveying in which field work and office work are done simultaneously on a Planetable. The field observations are taken and recorded side by side on the sheet fixed on the plane table and the map of the area is obtained. The use of field book is all together eliminated. It is most suitable for the survey of details between stations which have already being fixed by Theodolite or any other accurate method of surveying. It is commonly employed for small and medium scale mapping of comparatively large areas where gates accuracy is not the main consideration such as for topographical surveys. The equipment essentially needed for plane tabling is a Plane table or Drawing board which carries a drawing sheet and is mounted on a tripod stand and an alidade which provides line of site and a straight graduated edge.
                              
ADVANTAGES:

  1. It is one of the most rapid methods of surveying.
  2. Field notes are not required, and thus the possibility of mistakes in booking is eliminated.
  3. Measuring of lines and angles is mostly dispensed with since they are obtained graphically.
  4. Since the maps are plotted in the field, there is no chance of omitting necessary measurements.
  5. The surveyor is fully confident about the true representation of the area since he can always compare his work with actual features on the ground and cannot, therefore, outlook any essential detail.
  6. The surveyor can check the accuracy of his work more frequently and from any position he may desire, thus eliminating all the error at the spot.
  7. It is particularly suitable for filling in details in hilly areas and in magnetic areas where chain and compass surveys are not suitable.
  8. Contours and other irregular objects may be accurately represented on the map since the tract is in view.
  9. It is less costly than Theodolite survey.
  10. No great skill is required in making a satisfactory map and the work can be entrusted even to a subordinate.

EQUIPMENTS IN PLANE TABLE SURVEYING:

The equipments needed in plane table surveying are as follows: 

  1. Drawing Board & Tripod. 
  2. Alidade 
  3. Accessories

Drawing Board & Tripod:   The drawing board on which field measurements are plotted is fixed on the plane table or drawing board. The board is made of well seasoned good quality e.g., teak or pine and is available in sizes (I) 50 cm x 40x 1.5 cm. (ii) 50 cm 50 cm x 1.5 cm (iii) large 70 cm x 60 cm x 1.5 cm. The upper surface of the board must be perfectly plane. It is mounted on a tripod in such a way that it can be leveled rotated about vertical axis and clamped in any position. The tripod is generally of the open frame tie the board is sometimes fitted with leveling head or ball and socket arrangement for the purpose of leveling of the tube.


Alidade: The alidade is a state rule fitted with such an arrangement as to provide a line of sight. It is used for sighting objects and drawing rays along one of its leveled edges known as ruling or working or fiducial edge. The fiducial edge is graduated so as to serve a scale for plotting distances.

Accessories:

The accessories in plane table are:

  1. Trough compass: It is used for making the direction of the magnetic meridian on the sheet of plane table.
  2. Plumbing fork or U frame: It is also fitted with plumb bob and is used for centering the table.
  3. Spirit level: It is used for leveling the plane table.

Methods of Plane Table Surveying:
It may be classified under four headings:
1. Radiation.
2. Intersection.
3. Traversing.
4. Resection.
 
Traversing: This is the main method of plane tabling and is similar to that of compass or Theodolite traversing. It is used for running survey lines of a closed or open traverse.
 
Procedure:

  1. Select the traverse stations say A, B, C etc.
  2. Set up the table over one of them say A. select the point A suitably on the    sheet. Level  and centre the table over A.
  3. Mark the direction of magnetic meridian on the top corner to the sheet by means of trough compass.
  4. With the alidade touching A, sight B and draw the ray.
  5. Measure the distance AB and scale off AB, thus fixing the position of B on the sheet which represents their station B on the ground.
  6. Shift the table and set up at B with b over B and orient it by placing. The alidade along BA, turning the table until the line of sight strikes A, and then clamp it.
  7. With the alidade touching B sight C and draw a ray.
  8. Measure the line BC and cut off BC to scale.Proceed similarly at other stations, in each case orienting by back side before taking forward sight until all the remaining stations are plotted.
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Published: August 17, 2010   
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