In setting up a plane table at a station A, the corresponding point on the plan was NOT accurately centred above A. If displacement of A was 20 cm in direction at right angles to the ray, then how much on the plan would be consequent displacement of a point from its trre position (if scale is 1 cm = 2 m)?

This question was previously asked in

SSC JE CE Previous Year Paper 10 (Held on 30 Oct 2020 Evening)

Option 3 : 1 mm

ST 1: Building Material and Concrete Technology

18425

20 Questions
20 Marks
12 Mins

__Concept:__

Plane-table survey:

A plane table surveying is a graphical method of surveying. In this method of surveying, field observation and plotting are done simultaneously helping the surveyor to compare the plotted details with actual features of the ground.

Advantages of Plane Table Survey:

- It is suitable for the location of details as well as contouring for large-scale maps directly in the field.
- As surveying and plotting are done simultaneously
- The plotting details can immediately get compared with the actual objects present in the field. Thus errors, as well as the accuracy of the plot, can be ascertained as the work progresses in the field.
- The plane table survey is generally more rapid and less costly than most other types of survey.

Disadvantages of Plane Table Survey:

- The plane table survey is not possible in unfavorable climates such as rain, fog, etc.
- This method of survey is not very accurate and thus unsuitable for large-scale or precise work.
- As no field book is maintained, plotting at different scale require full exercise.
- The quality of the final map depends largely on the drafting capability of the surveyor.

**For the plane table set-up:**

From a similar triangle theorem:

\(\frac{\text{e}}{\text{aa }\!\!'\!\!\text{ }}=\text{S}\)Where S = Scale

__Calculation:__

Scale = \(\frac{\text{1}}{2\ \times\ 100 }=\frac{1}{200}\)

\(\frac{\text{e}}{20}=\frac{1}{200}\)

∴ e = 0.1 cm = 1 mm

__Important Points__

The setting of Instruments:

- Fixing
- Centering
- Leveling

Different methods for plane table survey:

- Radiation
- Intersection
- Traversing
- Resection