Short Answer

The methods of plane table surveying in civil engineering are different techniques used to plot maps directly in the field using a plane table. These methods help in locating points and drawing them on a sheet at the same time. The main methods are radiation, intersection, traversing, and resection.

Each method is used depending on field conditions and type of survey work. They make surveying simple, quick, and useful for preparing maps of small to medium areas where immediate plotting is required.

Detailed Explanation:

Plane table methods basics

The methods of plane table surveying in civil engineering are systematic techniques used to prepare maps directly in the field. In this surveying method, observations and drawing are done simultaneously on a drawing sheet fixed on a plane table.

These methods help surveyors locate points on the ground and represent them accurately on paper without waiting for later office work. Different methods are used depending on the type of area, visibility between points, and nature of survey work.

The main methods of plane table surveying are radiation, intersection, traversing, and resection. Each method has its own procedure and application in civil engineering projects.

Radiation method

The radiation method is one of the simplest methods of plane table surveying. In this method, all points are located from a single station.

The plane table is set at one point, and rays are drawn from this station to all visible points on the ground using an alidade. The distances of these points are measured and plotted on the drawing sheet.

This method is suitable for small open areas where all points are clearly visible from one location. It is commonly used for small maps, garden layouts, and small construction sites.

The main advantage of this method is its simplicity and direct plotting process.

Intersection method

The intersection method is used when distances cannot be measured easily. In this method, two different stations are used to locate a point.

The plane table is set at two known points, and rays are drawn from both stations toward the same unknown point. The point is located where these two rays intersect on the map.

This method is useful in rough or difficult terrain where direct measurement is not possible, such as hills or obstacles like rivers and buildings.

It improves accuracy when distance measurement is difficult but angle observation is possible.

Traversing method

The traversing method is used when a series of connected survey stations are to be mapped. The plane table is moved from one station to another in sequence.

At each station, the previous points are plotted, and new points are added by sighting and measuring directions. This process continues until the entire area is covered.

This method is commonly used for long surveys such as roads, canals, railways, and boundary mapping.

The traversing method is useful for covering large areas in a systematic way.

Resection method

The resection method is used to determine the position of the plane table station by sighting known points already plotted on the map.

In this method, the surveyor sets the table at an unknown point and then sights at two or more known points whose positions are already marked on the drawing sheet.

By drawing lines from these known points, the position of the current station is fixed at the point of intersection.

This method is useful when the exact location of the survey station is not known in the field.

It is commonly used in navigation and checking work during surveying.

Importance of plane table methods

The methods of plane table surveying are very important in civil engineering because they allow quick and direct mapping in the field.

They reduce the need for complex calculations and help in preparing maps instantly. This is useful for preliminary surveys and small to medium projects.

Each method is suitable for different field conditions, making plane table surveying flexible and practical.

These methods are widely used in rural mapping, road planning, building layouts, and small land surveys.

Conclusion

The methods of plane table surveying in civil engineering include radiation, intersection, traversing, and resection. Each method is used based on field conditions and survey requirements. These methods help in quick, simple, and direct mapping, making plane table surveying an important tool in basic civil engineering work.