The following four methods are available for carrying out plane table survey:

1. Radiation

2. Intersection

3. Traversing

4. Resection.

The first two methods are employed for locating details while the other two methods are used for locating position of plane table station on drawing sheet.

Radiation

After setting the plane table on a station, say O, it is required to find the plotted position of various objects A, B, C, D ….. . To get these positions, the rays OA, OB, OC ….. are drawn with soft pencil Then the distances OA, OB, OC ….., are measured scaled down and the positions of A, B, C ….., are found on the drawing sheets. This method is suitable for surveying small areas and is convenient if the distances to be measured

are small. For larger areas this method has wider scope, if telescopic alidade is used, in which the distances are measured technometrically.

Intersection

In this method the plotted position of an object is obtained by plotting rays to the object from two stations. The intersection gives the plotted position. Thus it needs the linear measurements only between the station points and do not need the measurements to the objects. shows the method for locating objects A and B from plane table positions O1 and O2.

This method is commonly employed for locating:

(a) Details

(b) The distant and inaccessible points

(c) The stations which may be used latter.

Traversing

This is the method used for locating plane table survey stations. In this method, ray is drawn to next station before shifting the table and distance between the stations measured. The distance is scaled down and next station is located. After setting the plane table at new station orientation is achieved by back sighting. To ensure additional checks, rays are taken to other stations also, whenever it is possible.

Resection

This method is just opposite to the method of intersection. In the method of intersection, the plotted position of stations are known and the plotted position of objects are obtained by intersection. In this method the plotted position of objects are known and the plotted position of station is obtained. If a, b and c are the plotted positions of objects A, B and C respectively, to locate instrument station P on the

paper, the orientation of table is achieved with the help of a, b, c and then resectors Aa, Bb, Cc are drawn to get the ‘p’ , the plotted position of P. Hence in the resection method major work is to ensure suitable orientation by any one of the methods. The following methods are employed in the method of resection:

(a) by compass

(b) by back sighting

(c) by solving two point problem

(d) by solving three point problem.

(a) Resection after Orientation by Compass:

(b) Resection after Orientation by Back Sighting:

(c) Resection after Solving Two Point Problem