What are the different methods of plane table surveying?

Short Answer:

The different methods of plane table surveying are radiation, intersection, traversing, and resection. Each method is used depending on the type of area being surveyed and the features that need to be plotted. These methods help in drawing lines and locating points on the map directly from the field.

In the radiation method, lines are drawn from a single station to various points. Intersection uses rays from two stations to fix a point. Traversing involves plotting a series of connected points, while resection helps determine the position of the table when it’s not known.

Detailed Explanation:

Different methods of plane table surveying

Plane table surveying is a method where the surveyor draws the map while observing the ground directly. To do this efficiently in different situations, four main methods are used. Each method has a specific purpose and is chosen based on the shape of the area, visibility of points, and access to the stations.

1. Radiation Method

In this method, the plane table is set up at a central station from where all the other points to be surveyed are visible. From this station:

  • Rays (lines) are drawn on the paper toward the features.
  • Distances to these features are measured using tape or chain.
  • The points are then plotted to scale along those rays.

Best used for: Small areas, open fields, and where all features are visible from one spot.
Example: Surveying a small park, garden, or playground.

2. Intersection Method

This method is used when distances to the points are hard to measure, but the points can be seen from at least two known stations. The process:

  • Set the plane table at the first station and draw rays toward the visible feature.
  • Move to a second known station and do the same.
  • The point where the rays from both stations meet is the location of the feature.

Best used for: Surveying across rivers or obstacles where you cannot directly measure distance.
Example: Plotting a tower or temple across a river.

3. Traversing Method

This method is useful for surveying long and narrow areas like roads, canals, or boundaries. It involves:

  • Setting up the plane table at successive stations.
  • Drawing lines between each station as the survey moves forward.
  • Plotting the path of the area with connected lines and noting side features.

Best used for: Surveying roads, pipelines, or property boundaries.
Example: Laying out a roadside plan or pathway.

4. Resection Method

This method is used when the surveyor’s location is not known but can see at least three known points already plotted on the map. Steps include:

  • Sight the known points from the unknown station.
  • Draw rays back toward them.
  • The point where all rays intersect gives the position of the instrument.

Best used for: Fixing the table’s position when starting from an unknown point.
Example: Surveying from a hilltop or unmarked area.

Each of these methods uses the same basic instruments—plane table, alidade, tripod, and drawing sheet—but the choice of method depends on site conditions and survey requirements.

Conclusion

The different methods of plane table surveying—radiation, intersection, traversing, and resection—are used based on the visibility, location, and layout of the area. These methods help surveyors draw accurate maps directly in the field, saving time and reducing errors.