What is the function of each instrument required for plane table surveying?
1 Answer

1. The plane table - Plane table is drawing a board of size 700mm× 600mm made of well season wood teak like, pine etc. The top surface of the table is well levelled. The bottom surface consists of a threaded circular plate for fixing the table on tripod stand by a wing nut.

plain table

2. The alidade- There are two types of alidade

  • Plain alidade- The plane alidade consist of a metal or wooden ruler of length about 50cm. one of its edges is bevelled and is known as the fiducial edge. It consists of two vanes at both ends which are the hinge with the ruler. One is known as object vane and carries a horse hair the other is called as a sight vane and it provides with a narrow silt.

plain alidade

  • Telescopic alidade- The telescopic alidade consist of a telescope meant for inclined sight and sighting distance objects clearly. This alidade has no vane at the end but it provides with the fiducial edge.

telescopic alidade

3. Spirit level- Spirit level is a small level tube containing a small bubble or spirit. The bubble is visible on the top along with a graduated glass tube. Spirit level meant for levelling the plane table.

spirit level

4. The compass- There are kinds of compass:

  • The through compass- The through compass is a rectangular box made of non-magnetic metal contain a magnetic needle pivoted at the centre this compass consists of a 0 mark on both ends to locate the N-S direction.

the through compass

  • Circular box compass- It carries a pivoted magnetic needle at the centre. The circular box fitted on square base plaSometimestime two bubble two fitted at right angle to each other on base plate. The compass is meant for making the north direction of map.

circular box compass

5. U fork or plumbing fork with plumb bob- The U fork is a metal strip bend in the shape of U having equal arm length. The top arm is pointed and bottom arm carries a hook for suspending a plumb bob.


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