Two Point Problem|Civil Easy Learning

PLANE TABLING METHODS 

Resection is a method of orienting the table. The objective is to plot the station occupied by the  

table rather than plotting other points. 

After resection, the station occupied by the table is  obtained on the sheet in correct orientation. 

The two-point and three-point problems are resection methods.

TWO-POINT PROBLEM 

The two-point problem can be stated as: 

“To find the position a on the table of the station A occupied by the table, given the  accurately plotted positions, p and q, of  two stations P and Q, visible from the  instrument station and by not occupying  

these two stations.”

Procedure -Two point Problem  :

1. Plot the points P and Q two well defined  points whose positions are plotted on  map as p and q. 

2. An auxiliary station B is selected at a  suitable position. The table is setup at B and levelled and oriented by eye position.  It is then clamped. 

3. Touching the alidade p and q the points P and Q are bisected and rays are drawn.  The rays will bisect at b.

4. Alidade is centred on b ranging rod A is  bisected and a ray is shown. 

5. A point a1 is marked on the ray. 

6. Shift the table and centred on A with a1 just over A. It is levelled and oriented by  back sighting.  

7.Keep the alidade touching the point p the  point P is bisected and a ray is drawn. The  ray intersects line ba1 at point a1 which  was assumed before.

8.Keep the alidade on a1 the point Q is  bisected and a ray is drawn. The ray  intersects bq at q1. A triangle is formed,  pqq1( This is the error triangle which  should be eliminated) 

9.The alidade is then placed along the line  pq1 and a ranging rod R is fixed at some  distance from the table. 

10.Alidade is placed along the line pq and  the table is turned to bisect RThe table is said to be perfectly oriented. 

11.Finally, the alidade cetered on p and q ,  the points P and Q are bisected and rays  are drawn. The rays intersect at a point a. This would represent the exact position of  the required station A. 

12. Station A is marked on the ground.