Error due to Centering in Plane Table Survey

In plane table surveying, the process of centering involves setting up the plane table over a point on the ground from where the survey is to be conducted. It is essential to ensure that the table is accurately centered to minimize errors in the survey measurements. One such error is the misplacement of the station point, which can lead to inaccuracies in the plotted positions of the various survey points.

Significance of Scale in Plane Table Survey

The scale is an important aspect of a plane table survey as it determines the ratio between the distances on the map or drawing and the actual distances on the ground. It allows for the representation of large areas on a smaller piece of paper. The scale is usually expressed as a representative fraction (RF) or a graphic scale.

Error Due to Centering

The error due to centering in plane table surveying occurs when the station point is not accurately positioned on the ground. This misplacement can lead to the incorrect plotting of survey points and subsequent errors in the survey measurements. The error due to centering is dependent on various factors such as the accuracy of the centering process and the scale used in the survey.

Relation Between Error Due to Centering and Scale

The error due to centering should not exceed the scale divided by a certain factor. This factor represents the maximum allowable error due to centering, beyond which the accuracy of the survey may be compromised.

Calculation of Maximum Allowable Error

To calculate the maximum allowable error due to centering, the scale is divided by the factor specified in the question. In this case, the correct answer is option 'B,' which states that the error due to centering should not exceed the scale divided by 40.

For example, if the scale of the survey is 1:5000, the maximum allowable error due to centering would be 1/40 * 5000 = 125 units. This means that the misplacement of the station point should not exceed 125 units on the ground.

Importance of Limiting the Error Due to Centering

Limiting the error due to centering is crucial in achieving accurate survey measurements. Any misplacement of the station point can lead to cumulative errors in the plotted positions of the survey points. These errors can affect the overall reliability and precision of the survey data, leading to incorrect interpretations and decisions based on the survey results.

Conclusion

In plane table surveying, it is important to minimize the error due to centering to ensure the accuracy of the survey measurements. The maximum allowable error due to centering is determined by dividing the scale by a specified factor. Option 'B' in this question correctly states that the error due to centering should not exceed the scale divided by 40. By adhering to this criterion, surveyors can obtain reliable and precise survey data for various engineering and construction projects.