Plane Table Survey, Principle, Merits & Demerits, Instruments and Setting Up

Plane Table Survey, Principle, Merits & Demerits, Instruments and Setting Up

Plane table surveying is a graphical method of surveying in which field observations and plotting are carried out simultaneously. It is widely used for small-scale surveys where quick and direct mapping is required. For Surveyor trade trainees, understanding the principle, instruments, and setup of plane table surveying is essential.

Plane Table Survey

Plane table survey involves drawing the map directly in the field using a plane table and alidade. It eliminates the need for extensive field notes and allows immediate visualization of the survey area.

Principle of Plane Table Survey

The main principle of plane table surveying is:

• Parallelism: The lines drawn on the paper are kept parallel to the corresponding lines on the ground.

This means that the orientation of the table must be maintained correctly so that the plotted lines represent the actual field positions accurately.

Merits of Plane Table Survey

• Fieldwork and plotting are done simultaneously
• No need for field book recording
• Errors can be detected and corrected on the spot
• Simple and economical method
• Suitable for small areas and preliminary surveys

Demerits of Plane Table Survey

• Less accurate compared to modern methods
• Not suitable for large or complex areas
• Affected by weather conditions (rain, wind)
• Requires clear visibility of points
• Drawing sheet may expand or shrink due to moisture

Instruments Used in Plane Table Survey

• Plane Table: A flat board mounted on a tripod used for drawing
• Alidade: Used for sighting objects and drawing lines
• Tripod Stand: Supports the plane table
• Plumbing Fork and Plumb Bob: Used for centering
• Spirit Level: Used for levelling the table
• Trough Compass: Used for orientation
• Drawing Sheet and Accessories: Used for plotting

Setting Up of Plane Table

Proper setting up of the plane table is essential for accurate surveying. It involves three main operations:

1. Centering

Centering is the process of placing the plane table exactly over the survey station. This is done using a plumbing fork and plumb bob.

• Ensures correct positioning of the table
• Reduces errors in plotting

2. Levelling

Levelling ensures that the plane table is perfectly horizontal. This is done using a spirit level by adjusting the tripod legs.

• Allows accurate drawing
• Prevents distortion of measurements

3. Orientation

Orientation is the process of aligning the plane table so that it remains parallel to its previous position.

Methods of orientation:

• By Compass: Using trough compass to align north direction
• By Back Sight: Aligning with a previously plotted line

Precautions While Setting Up

• Ensure proper centering over the station
• Level the table accurately
• Maintain correct orientation
• Fix the drawing sheet firmly
• Avoid movement during observation

Applications of Plane Table Survey

• Topographical surveys
• Small area mapping
• Preliminary surveys
• Military and reconnaissance surveys

Importance in Surveyor Trade

Plane table surveying helps students understand the relationship between field observations and map drawing. It develops practical skills and improves visualization of survey data.

Conclusion

Plane table survey is a simple and effective method for quick mapping. Understanding its principle, instruments, and setup procedures is essential for accurate surveying work.

For ITI Surveyor trainees, mastering plane table surveying provides a strong foundation for advanced surveying techniques.