upendra kumar

The principle of the plane table is the law of parallelism. The line drawn station to object on the paper is parallel to the line of sight station to object on the ground.  

In the plane table survey, the fieldwork and plotting work is done simultaneously. It is most suitable for detailed surveys.

Advantage:- It is suitable for a small scale.
                      It is the most rapid.
                      No mistakes occur in booking field books because field books are not required.
                      The surveyors can easily check to plot work in the field.
                      Contour and irregular objects plotted accurately.
                      There is no chance of omitting any measurement.
                       It is less costly.

Disadvantage:- It is not suitable for a wet climate.

plane table

Accessory:-  A. The Tripod:- A Tripod is required for setting the plane table. It is made of wood.    
 B. The Drawing board:- The drawing board is made of wood and its size varies 4ocm×30cm to 50cm×60cm. It is mounted on a tripod in a level position and revolved through a vertical axis.                 
  C. The Alidade:- The Alidade is made of brass or gunmetal. In the observation time the line of sight of alidade is parallel to working or fiducial edge of alidade.

   D. The Compass:-    The through or circular compass is used for the setting of the direction of paper and table.  
   E. Level tube:- Level tube is used for setting the table in a level position.

   F. The plumbing fork or U frame:- It is used for centering purposes.

   G. Other drawing materials:- paper, drawing pins, clips, clamps, pins, pencils, rubber, Scale, etc. 

Setting up the plane table:- The level of the tripod is spread apart and kept at working height. The legs are fixed into the ground.

 The table should be so placed over the station on the ground that the point plotted On the sheet corresponding to the station occupied should be exactly over the Station on the ground. This made use of a U frame. To do this place the pointed end Of the upper leg of the form coinciding with the point on the paper and suspended a Plumb line from the other leg. Shift the table bodily until the plumb bob hangs over The center of the station peg. The Table is then leveled by use leveling tube. The level table keeps on parallel and Perpendicular direction, and level by the movement of legs.


Orienting the table. The preparation of keeping the table at each of the successive stations parallel
 To the position which it occupied at the first station is known as orientation. It carries on  Two ways.

  1. Orientation by the magnetic needle. Keep the compass on the table and turned the table until 
            The magnet read zero. Then clamped the table.
  1. Orientation by back sight:-In this method the table is oriented by use of the line of sight parallel to a line drawn on the paper. Let us a line be drawn on the paper. Set the table at station B on the ground, make the center, and level of the respect of b point on the paper.  Turn the table until the line of sight of BA is parallel to ba on the paper.


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