Which method of plane tabling is used when the distance between the point and the instrument station is too large?

Question

Question

This question was previously asked in

RRB JE CBT 2 (Civil Engineering) ReExam Official Paper (Held On: 04 Jun, 2025)

Answer 1

Explanation:

Methods of the plane table:

1. Radiation:

In this method, the instrument is setup at a station, and rays are drawn to various stations which are to be plotted.
This method is suitable only when the area to be surveyed is small and all the required stations to be plotted are clearly visible and accessible from the instrument station.

2. Traversing:

This method is similar to compass or theodolite traversing. The table is set at each of the stations in succession.
This method is most suited when a narrow strip of the terrain is to be surveyed, e.g. survey of roads, railways, etc.

3. Intersection:

This method is suited when the stations are not visible or the distance between stations is too large. Or in other words, this method is suitable for locating inaccessible points.
In this method, two stations are selected such that all the other stations to be plotted are visible from these.
Sometimes this method is also called graphical triangulation.

4. Resection:

This method of orientation is employed when the plane table occupies a position not yet plotted on the drawing sheet.
Resection can be defined as the process of locating the instrument station occupied by the plane table by drawing rays from the stations whose positions are already plotted on the drawing sheet.
This method is employed when the surveyor feels that some important details can be plotted easily by choosing any station other than the triangulation stations.

Hence both statements are correct.

Additional Information

Plane Table surveying:

The plane table is an instrument used for surveying by a graphical method in which the fieldwork and plotting are done simultaneously.
The main feature of plane tabling is that the topographic features to be mapped are in full view. Hence no chance of missing any important detail.
It is suitable for small and medium scale mapping, where great accuracy is not required.
It is also used for plotting the topographical maps in the field.
Before commencing a plane table surveying, the instrument stations are fixed to cover the entire area.
This graphical method of producing topographic maps is known as cartographic surveying.
The principle used in plane table surveying is that an unknown point of interest can be established by measuring its direction from known points.