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How to use the Plane table

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Rural Technology

We are now going to draw a map of a school ground. The following operations should be performed while setting up the table at a station: Initially select a point from where all points will be seen.

  • 1) The legs of the tripod should be spread well apart, and firmly rested on the ground.
  • 2) Centering of the table is done by using plumb bob. If no plumb bob is available, centering of the table may be done by dropping a stone from a point on the underside of the board which is directly under the point on the paper.

The table is then leveled by means of the leveling screws with reference to the level tube or spirit level, placed on the table first parallel to the two screws and then over the third screw. Method of drawing map Point A is marked on the paper, coinciding with point A on the ground. Other points viz. B, C, D are on the ground are seen from alidade. Actual distance of point A and point C is measured using meter tape. A suitable scale is selected considering dimension of the paper and actual distance between the points. According to the scale, a line corresponding point A to B is drawn on the paper using pencil. All point B, C, D… etc. are marked on the paper and joined with the A. Map is drawn by joining peripheral (B,C,D etc.) points in sequence on the field on paper. (Sample image of the hand drawn map is shown in fig.1.6) Precautions while drawing the map Following precautions need to be taken:

  • 1) The board should be horizontal.
  • 2) The table should be accurately centered.
  • 3) The table should be correctly oriented.
  • 4) The objects should be sighted accurately.
  • 5) The alidade should be correctly centered on the station point.
  • 6) Plotting should be done accurately.
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