PLANE TABLE SURVEYING

 PLANE TABLE SURVEYING

Plane table is a method of surveying, which involves graphically plotting and carrying out observations at the same time. In a nutshell it is a way to make a manuscript map in the field. It can deploy both topography control and triangulation/traverse as per requirement. 

INSTRUMENTS USED

Plane table surveying uses the following instruments:

• A plane table with leveling head 
• An alidade for sighting
• Plumbing fork and plumb bob 
• Spirit level 
• Compass
• Drawing paper 
• Masking tape 

PROCEDURE FOR SURVEYING

Plane table involves three steps to carry out survey:

• FIXING
• SETTING
• SIGHTING THE POINTS

FIXING: It involves fixing the plane table on tripod stand and making sure it is parallel to the ground with the help of spirit level and plumb bob. 

Care must be given to ensure that the table is levelled from all it's corners.

SETTING: After table is levelled, it should be placed over the station on the ground so that the point plotted on the sheet corresponding to the station occupied comes exactly over the station on the ground. 

This specific step is known as centering of plane table. 

ORIENTATION: Orienting involves, placing the plane table in a fixed direction to make sure the line representing a certain direction on the plan is parallel to the direction on the ground. There are 2 ways of orientation:

• Orientation with the help of compass 
• Orientation by backsighting

SIGHTING THE POINTS: After the table has been set and orientation is carried out, points to be located are sighted with the help of alidade. Alidade is pivoted about the plotted location of the instrument station  and turned to make sure the line of sight passes through the signal at point to be plotted. 

From there, a ray is drawn from the instrument station along the edge of alidade. Following this, rays over other points to be sighted are drawn. 

Finally, the points are plotted on sheet.