Methods of Plane Tabling
In this position the point is located on plane by drawing a ray from the plane table station to the point, and plotting scale along the ray the distance is measured from the station to the point. The method is suitable for the survey of the small areas which can be commanded from a single station.
In this method the point is fixed on plane by the intersection of the rays drawn from the two instrument stations. The line joining at these stations is called the base line.
This method is similar to that of compass or transit traversing. It is used for running survey lines between stations which have been previously fixed by other methods of surveying to locate the topographical details. It is also suitable for the survey of roads, rivers etc.
This method is used for establishing the instrument stations only. After fixing the station, details are located either by radiation or intersection. The characteristic feature of resection is that the point plotted on plan is the station occupied by the plane table.
Select appoint p so that all point to be located are visible from it.
Set up the table at p and leveled.
Marked the direction of magnetic meridian with through compass in top corner of sheet.
Select the point p on the sheet so that it is exactly over station p on the ground.
Centering the Alidades on p, sight the various points A, B, C etc. and draw the rays along edge of Alidades.
Measure the distance PA, PB, PC etc. from p to various point with chain or tape and plot them to scale along the co responding rays. Join the points a, b, c, etc. to give outline of survey.
Select two point P and Q in a commanding position so that all points to be plotted are visible from P and Q. Line joining these points are called base line. Set the table over P and mark direction of magnetic direction of magnetic meridian by means of through compass. Alidade pivoted on point P, sight the station Q and other object a, b. c, d, e, and draw rays along the edge of alidade towards Q, A, B, D, and E. measured distance from P and Q accurately and along the rays drawn towards Q. Now shift the table and set it up at point Q and adopt same procedure.