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The method of conducting plane table surveying

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The plane table surveying is considered as one of the rapid and simplest methods of surveying. With plane table surveying, it is also possible to execute plotting of plans and field observations. This type of surveying can be conducted for the following situations :-

1. It is mostly suited for small-scale surveying i.e. different types of fields.
2. It can also be conducted surveying industrial areas where compass survey can’t be applied.
3. It is frequently applied to fill in details among stations fixed by triangulation method or theodolite traversing method.

Systems of Plane Table Surveying

Radiation: It is the easiest method that can be applied when the complete surveying should be carried out from one single station i.e. the table will remain in such a position from where all the other points of the field can be viewed easily. It is performed in the following ways :-

i. A point P should be chosen in such a manner that all the other points ( A B C D E) can be observed easily from P.
ii. Centering, leveling, and orientation should be performed before surveying.
iii. Initially, by putting the alidade on point P, a line of sight for station A should be drawn.

iv. Once the distance of PA is calculated on field, the measurement should be provided on paper to a appropriate scale.
v. In the same way, points b, c, d, and e are acquired on paper by drawing lines of sight for stations B, C and D and calculating the distances PB, PC, PD and PE on ground correspondingly.
vi. Points a, b, c, d, and e are attached on paper.

Intersection: For a mountainous terrain or rough surface, the distances can’t be adopted physically. In this situation, intersection method will be suitable. It is conducted in the following ways :-

Also Read: Definition of leveling and some vital terms used in surveying & leveling

i. Two stations O1 and O2 are chosen in order that the points being placed on paper are easily visible from them.
ii. The plotting for the baseline (o1o2) is done on the paper. The table is centered and leveled at station O1 and then after orienting at station O2, the distance O1 O2 are properly calculated and set up to some scale on the paper. The line o1o2 is drawn to some scale on the paper and then the board is modified from station O1 by back sighting at station O2.
iii. From station O1, rays for stations A, B are drawn etc.
iv. Now, shift the table to the new station and orient it and again the rays of stations A, B are drawn etc.,
v. The meeting point of rays from stations O1 and O2 will provide points a, b etc. on paper.

Traversing Method: It has similarity with the compass survey to some extent. It is suitable for running survey lines among stations, which are fixed earlier by other methods of survey, to trace the topographic details.

i. The plane table is set at a location (say A).
ii. From that point, a sight is picked up toward B and the distance AB is calculated.
iii. The plane table is moved to station B and sighted toward A (it is known as back sighting). Distance BA was calculated.
iv. The average distance among AB and BA are plotted to proper scale on the drawing paper.
v. Then the point C is sighted from B and the distance is calculated. This process is reiterated for all the stations.
vi. Perform some check at equal spans. Lastly, plot the traverse lines on the drawing sheet. Ensure that back sighting was performed only for the first two stations.

Resection Method: This method is adopted for setting up new stations at a place with the purpose of finding out the missing details. It is the method of finding out the position (plotted earlier) of any peg station with the help of sight picked towards known points, the location of which is plotted.

Resection method comprises of the following processes:

1. The three-point problem
2. The two-point problem

Two Point Problem: Under this problem, two separate points are chosen whose location is recognized and plotted on the drawing paper. The two points are attached and bisected precisely. The bisecting point is taken as the new station.

The method of conducting plane table surveying