What is Plane Table Survey?

In the field of civil engineering, the accuracy and efficiency of surveying methods directly impact the quality of construction and development projects. One of the traditional yet effective methods of land surveying is the plane table survey. Despite the rise of advanced digital tools and satellite-based systems like GPS, the plane table remains a practical choice for many field engineers, especially in preliminary surveys and educational applications.

This article explores everything you need to know about plane table surveying—from its definition and methods to the instruments involved, advantages and disadvantages, and its modern-day relevance. Whether you're a student, a budding civil engineer, or a professional looking to revisit foundational methods, this comprehensive guide is your ultimate resource.

What is Plane Table Surveying?

Plane table surveying is a graphical method of surveying in which the fieldwork and plotting are done simultaneously on a drawing board (or plane table) mounted on a tripod. Unlike other surveying methods that involve recording data and plotting later, this method allows surveyors to draw maps directly while observing the terrain.

The plane table method is particularly useful for small-scale surveys where high precision is not critical. It enables real-time mapping and visualization, which can significantly speed up the surveying process. Despite being a traditional method, it continues to be taught in educational institutions and used in specific field scenarios.

4 Methods of Plane Table Surveying for Civil Engineers

Surveyors can apply different techniques depending on the nature and requirements of the project. The four primary methods of plane table surveying are:

Radiation Method of Plane Table Surveying

The radiation method involves selecting a central station from which rays are drawn to various points in the terrain. The distances are then measured and scaled on the plane table. This method is particularly useful when the area to be mapped is visible from a single point.

Steps:

1. Fix the plane table and orient it properly.

2. Identify a central point and mark it on the drawing sheet.

3. Sight the surrounding features using the alidade.

4. Draw rays to these features and scale the distances accurately.

Traversing Method of Plane Table Surveying

The traversing method involves surveying a series of connected lines that form a traverse. This is ideal for long, narrow areas like roads, rivers, or pipelines.

Steps:

1. Begin from a known point and set the plane table.

2. Draw a line using the alidade and measure the distance.

3. Move to the next station and repeat the process.

4. Plot all stations and features along the traverse.

Intersection Method of Plane Table Surveying

The intersection method helps locate inaccessible points by taking angular observations from two known stations. It is ideal for mountainous or obstructed areas.

Steps:

1. Set up the plane table at two known points A and B.

2. Sight the inaccessible point P from both A and B.

3. Draw rays from A and B toward P— the intersection gives the location of P.

Resection Method of Plane Table Surveying

The resection method is used when the surveyor is at an unknown point, and the positions of surrounding points are known. It is commonly used for orientation and location fixing.

Steps:

1. Orient the plane table roughly.

2. Sight at least three known points using the alidade.

3. Draw rays from these points— their intersection gives the location of the unknown station.

7 Key Instruments used in Plane Table Surveying

Several instruments are required to carry out plane table surveying effectively. These tools help the surveyor measure angles, distances, and ensure the plane table is properly set up for accurate results.

Drawing Board

The drawing board is the primary instrument used in plane table surveying. It is a flat surface on which the surveyor places a paper or cloth sheet to draw the map. The plane table is typically mounted on a tripod and set up at the survey site. The drawing board is the base for transferring field observations to a detailed map.

Alidade

An alidade is a sighting device used in plane table surveying to measure angles. It is typically a straightedge with a sighting mechanism at one end. The surveyor uses the alidade to take accurate angle measurements between their position and various points on the terrain.

Spirit Level

A spirit level is used to ensure that the plane table is level during the surveying process. This instrument is essential for maintaining accuracy in the field, as an uneven plane table can lead to distorted measurements and inaccurate maps.

Trough Compass

A trough compass is a type of compass that is mounted on the plane table. It helps the surveyor orient the plane table to magnetic north, ensuring that the survey is conducted with proper alignment. It is typically used in conjunction with the alidade to measure bearings and directions.

Plumbing Fork

The plumbing fork is used to ensure that the plane table is properly aligned with the vertical axis. It helps the surveyor maintain the correct position of the table while taking measurements. The plumbing fork is particularly useful when the surveyor needs to ensure precise positioning of the plane table over a fixed point.

Waterproof Cover

A waterproof cover is essential in plane table surveying to protect the drawing sheet and equipment from adverse weather conditions. Surveyors often work outdoors in various weather environments, and keeping the instruments dry is crucial for accurate mapping.

Tripod

A tripod is used to support the plane table during surveying. It ensures that the table is stable and secure while the surveyor takes measurements. The tripod's height and stability are crucial for maintaining the accuracy of the survey, particularly when the surveyor needs to adjust the plane table to a specific angle or position.

Pros and Cons of Plane Table Surveying

Advantages of Plane Table Surveying

Real-Time Field Mapping

One of the biggest advantages of plane table surveying is that it allows for real-time mapping. Surveyors can directly transfer their observations onto the drawing sheet in the field, eliminating the need for additional data processing. This feature is particularly useful in emergency situations or projects where quick results are needed.

Cost-Effective Method

Plane table surveying is a cost-effective method compared to more advanced surveying techniques that require expensive equipment. The instruments used in plane table surveying are relatively affordable and easy to transport, making it an excellent choice for small and medium-scale projects.

Simple and Easy to Use

The plane table is a simple and intuitive tool, making plane table surveying easy to learn and implement. Surveyors do not require advanced technical skills to operate the instruments, which is why this method is commonly taught in basic surveying courses.

Suitable for Small and Medium Areas

Plane table surveying is ideal for mapping small to medium-sized areas, such as construction sites, parks, and agricultural land. It is particularly effective in urban and rural settings where precise vertical measurements are not always necessary.

Independence from Complex Equipment

Unlike other modern surveying techniques that rely on complex equipment like GPS or total stations, plane table surveying does not require advanced technology. This makes it an excellent choice for remote areas or projects with limited access to modern instruments.

Disadvantages of Plane Table Surveying

Limited Precision

While plane table surveying is an effective method, it does not offer the level of precision found in more advanced techniques like total station or GPS surveying. This can be a limitation when surveying large or highly detailed areas that require high accuracy.

Weather Dependency

Since plane table surveying is done outdoors, it is highly dependent on the weather. Rain, strong winds, or other adverse weather conditions can interfere with the surveyor's ability to take accurate measurements and complete the mapping process.

Cumbersome Setup

Setting up the plane table can be time-consuming, especially in areas with difficult terrain. Surveyors must ensure that the plane table is level and properly aligned, which can be a cumbersome task when working in uneven ground.

Requires Stable Ground

The plane table must be set up on stable, level ground to ensure accurate measurements. In areas with uneven terrain or where the ground shifts frequently, it may be difficult to maintain the stability needed for precise surveying.

Objectives of Plane Table Surveying

The main objective of plane table surveying is to create accurate and detailed maps of a surveyed area. Surveyors use this method to measure and record the layout of land features, including roads, buildings, and natural landmarks. The method is particularly useful for creating topographic maps, which can be used for urban planning, land development, and infrastructure projects.

Other key objectives of plane table surveying include:

• Mapping small to medium-sized areas with moderate precision

• Surveying land features for construction or development purposes

• Creating detailed maps that can be used for land ownership or resource management

• Providing real-time field data for analysis and planning

Principles of Plane Table Surveying

The principles of plane table surveying are based on basic geometrical concepts such as angle measurement, distance measurement, and triangulation. Surveyors use these principles to accurately map the terrain and create a scaled representation of the area.

Key principles include:

• Angle Measurement: Surveyors measure the angles between the plane table and fixed points in the area to determine the layout of the land.

• Distance Measurement: While plane table surveying does not always involve precise distance measurements, surveyors use indirect methods like triangulation to estimate distances.

• Leveling: Ensuring that the plane table is level is crucial to accurate measurements, as any deviation from level can cause distortions in the final map.

Conclusion

Plane table surveying is a valuable and cost-effective method used to create detailed maps and survey land in real-time. While it may not offer the precision of modern surveying techniques, it is an excellent tool for civil engineers and land surveyors working on smaller projects, in remote areas, or when simplicity and affordability are essential.

By understanding the different methods, instruments, and techniques involved in plane table surveying, engineers and surveyors can effectively apply this technique to a wide range of surveying tasks, ensuring accurate and reliable results. Whether you're surveying a small construction site or mapping out land for a development project, plane table surveying remains an essential and accessible tool in the field of surveying.

FAQs

What is the main advantage of plane table surveying?

The main advantage of plane table surveying is its ability to provide real-time field mapping, which allows surveyors to draw accurate maps directly in the field without the need for complex equipment or data processing.

Can plane table surveying be used for large areas?

Plane table surveying is best suited for small to medium-sized areas. For larger areas, more advanced techniques like total stations or GPS surveying may be more appropriate for achieving the required accuracy.

What instruments are essential for plane table surveying?

Key instruments for plane table surveying include a drawing board, alidade, spirit level, trough compass, plumbing fork, waterproof cover, and tripod.

Is plane table surveying still used today?

Yes, plane table surveying is still used today, especially for small-scale projects, topographic surveys, and in remote areas where modern equipment is not accessible.

How accurate is plane table surveying?

The accuracy of plane table surveying depends on several factors, including the skill of the surveyor, the method used, and the terrain. While it is not as precise as modern methods like GPS or total stations, it is sufficiently accurate for many applications.