# Introduction of Plane Table Surveying

Plane table surveying is a technique used in land surveying to accurately map out and measure the features of a given land area. It involves the use of a special instrument called a plane table, which allows for the direct drawing of the features on a paper sheet. This method has been used for centuries and has been a vital tool for surveyors, engineers, and cartographers in various fields. In this article, we will explore the basics of plane table surveying, its history, applications, and the different techniques used in this traditional yet highly effective surveying method. With the advancement of technology, the use of plane table surveying may have diminished, but its relevance and accuracy in certain situations cannot be denied. So, let’s delve into

## Objectives of Plane Table Surveying

Plane table surveying is a traditional and widely used method of land surveying that involves the use of a drawing board or plane table, a surveying instrument, and a tripod. The instrument is used to measure horizontal angles and distances between points on the ground, while the plane table serves as a reference for plotting these measurements on a map. The objectives of plane table surveying include:

1. Topographic Mapping: One of the primary objectives of plane table surveying is to create an accurate and detailed map of the land being surveyed. This map can be used to identify physical features such as hills, valleys, rivers, and other landscape elements. It is essential for planning and designing infrastructure projects, land development, and resource management.

2. Establishment of Control Points: Plane table surveying is also used to establish control points, which are fixed reference points on the ground used as a basis for other surveys. These points are marked with a permanent monument or reference point and are essential for future surveys in the area.

3. Measurement of Angles and Distances: The primary function of plane table surveying is to measure horizontal angles and distances between points on the ground. This data is used to create accurate maps and plans, as well as to determine the location and direction of objects and features on the land.

4. Area and Volume Calculation: Another objective of plane table surveying is to calculate the area and volume of a given area of land. This information is vital for various purposes, such as determining the quantity of materials needed for construction projects, estimating the productivity of agricultural land, and assessing the capacity of reservoirs and other water bodies.

5. Alignment and Layout: Plane table surveying is also used for aligning and laying out structures and other features on the ground. This includes roads, pipelines, buildings, and other infrastructure projects. The surveyor uses the data collected to determine the correct location, direction, and alignment of these structures for accurate construction.

6. Monitoring Changes in the Land: With regular plane table surveys, it is possible to monitor changes in the land over time. This is important for understanding the impact of natural and human factors on the landscape, such as erosion, deforestation, and urbanization.

In conclusion, the primary objectives of plane table surveying are to create accurate maps, establish control points, measure angles and distances, calculate area and volume, align and layout structures, and monitor changes in the land. Its practical and versatile nature makes it a valuable tool for land surveying and engineering projects.

## Principle of Plane Table Surveying

The principle of plane table surveying is used to determine the horizontal position and relative elevation of points on a land surface. It involves the use of a plane table, a mechanical or electronic device, to plot the survey data accurately. This surveying technique is commonly used in topographic mapping, engineering studies, and land development projects.

The following are the key principles of plane table surveying:

1. Stationing and Orientation: In a plane table survey, the table is set up at a predetermined point on the ground called the “station”. The table is then leveled and oriented with respect to the reference direction, typically the North-South line. The stationing and orientation process ensures that all the measurements are taken from a common reference point and direction.

2. Sight Reduction: Once the table is set up and oriented, the surveyor uses a sighting device, such as an alidade, to establish the line of sight between the reference point and the target point. The target point is usually a prominent feature or a point marked on the ground, such as a tree or a stake. This process is repeated for all the points to be surveyed.

3. Sketching: As the measurement is taken, the surveyor uses a pencil to plot the lines on the paper attached to the table. These lines represent the target points in relation to the reference point. The surveyor also labels each point with its respective code or name for identification.

4. Interpolation: After all the points are plotted, the surveyor uses the lines and their intersection points to determine the relative position and elevation of each point. Interpolation involves estimating the location of the target points that fall between the known points.

5. Field Book: To record the data accurately, the surveyor maintains a field book, which contains all the information regarding each survey point, including its code, elevation, and any remarks. This field book serves as a permanent record and can be used in the future for referencing.

6. Leveling: In some cases, vertical distances are also required in a plane table survey, such as when determining the relative elevation of points. To achieve this, the surveyor uses a leveling instrument to measure the height difference between two points. This data is then used to calculate the elevation of each point.

7. Accuracy: The accuracy of the plane table surveying primarily depends on the skill and experience of the surveyor. However, factors such as the quality of the equipment, weather conditions, and terrain type can also affect the accuracy of the survey.

In conclusion, the principle of plane table surveying focuses on achieving accurate and precise measurements by referencing all the data from a single point. With technological advancements, plane table surveying has evolved to use electronic devices such as Total Stations and Global Positioning Systems (GPS), which have improved the accuracy and efficiency of this surveying technique.

## Equipment Used in Plane Table Surveying

Plane table surveying is a type of surveying method in which a plane table with a sighting device is used to lay out the plan and map of the area being surveyed. This technique is especially useful for small, detailed surveys of a limited area. Here are some of the equipment used in plane table surveying:

1. Plane table: A plane table is a basic equipment used in this type of surveying. It is a sturdy, flat table with a smooth surface that allows for drawing and measuring. The table is usually made of wood, fiberglass, or metal and has adjustable legs for stability.

2. Alidade: An alidade is a sighting device attached to the plane table. It consists of a vertical frame with a horizontal graduated scale and a telescope mounted on it. The telescope is used to view the objects in the survey area and take bearings accurately. The horizontal scale is used to measure the distance between the objects.

3. Compass: A compass is an important tool used in plane table surveying. It helps in determining the direction of the survey lines and angles of intersection. A prismatic compass or a surveyor’s compass is commonly used in this method.

4. Plumb bob: A plumb bob is a weight attached to a string that hangs vertically from the underside of the plane table. It helps in finding the vertical lines and establishing the exact locations of the survey points.

5. Drawing board: A drawing board is used to secure the plane table on the field and provide a stable surface for drawing. It is usually made of wood or metal and has adjustable legs for stability.

6. Trough compass: A trough compass is a device that consists of two movable arms with pointed ends. It is used to transfer the survey lines from the plane table to the drawing sheet.

7. Drawing sheet: A drawing sheet is a paper or cloth sheet on which the plan and map of the surveyed area are drawn. The sheet is mounted on the plane table and fixed with tacks to keep it in place.

8. Measuring tape: A measuring tape is used to measure the distance between the objects on the survey area. It is essential to have a measuring tape with high accuracy for precise measurements.

9. Ranging rods: Ranging rods or ranging poles are used to mark points on the ground in the survey area. They are made of wood or metal and are painted in bright colors for easy visibility.

10. Drawing instruments: Drawing instruments such as pencils, rulers, protractors, and erasers are used to make precise measurements and draw accurate lines on the drawing sheet.

Overall, the equipment used in plane table surveying is relatively simple, compact, and easy to carry. However, they are essential for accurate and detailed surveying of small areas. The use of these instruments, combined with proper surveying techniques, ensures reliable and precise results.

## Temporary Adjustment of Plane Table

A plane table is a basic surveying instrument used for measuring horizontal angles and distances on a flat surface. It consists of a flat table or drawing board and a leveled tripod stand. The table is mounted on the tripod stand and its orientation is fixed by centering it over a known point on the ground. The surveyor then uses a sighting alidade to measure angles and a measuring chain or tape to determine distances.

Temporary adjustment of a plane table is an important aspect of using this instrument for accurate surveying. It involves the process of ensuring that the table is level and accurately positioned relative to the known point used for orientation. This adjustment is necessary before starting any survey work to ensure that the measurements obtained are correct.

There are two types of temporary adjustments for a plane table – levelling and centering.

Levelling adjustment is done to ensure that the table is horizontal or level. It is essential because any slight tilt or unevenness in the table can result in incorrect measurements. The following steps are followed for levelling adjustment:

1. Place the tripod stand on the ground and ensure that it is stable and firmly fixed.
2. Adjust the legs of the tripod to make it level by moving them in or out as required.
3. Set up the plane table on the tripod stand and tighten the clamps to secure it.
4. Use a spirit level to check the level of the table. If the bubble is not in the center, adjust the screws at the base of the table to level it.
5. Repeat the process until the bubble remains in the center when the table is rotated in all directions.

Centering adjustment is done to ensure that the table is correctly oriented over the known point of reference. This is essential because any displacement of the table from the reference point will result in incorrect measurements. The following steps are followed for centering adjustment:

1. Place the plane table over the known reference point.
2. Visually align the lines marked on the table with the reference point.
3. Use the plumb bob to check whether the line on the alidade corresponds with the reference point on the ground. Adjust the table if there is any misalignment.
4. Repeat the process until the line on the alidade matches with the reference point on the ground.

Both levelling and centering adjustments are equally important and must be done carefully to ensure accurate surveying. The correct temporary adjustment of a plane table will result in reliable and precise measurements, laying the foundation for an accurate survey. Any errors in the adjustment can lead to incorrect data and ultimately affect the results of the survey.

In conclusion, temporary adjustment of a plane table is an essential process in surveying that ensures accurate measurements. It involves levelling the table to make it horizontal and centering it correctly over the known reference point. These adjustments must be done carefully and accurately to obtain reliable data and achieve successful survey results.

## Methods of Plane Table Surveying

Plane table surveying is a type of basic surveying method where a flat table is used as the main instrument for measuring horizontal distances and angles. This method is widely used in small-scale surveys, particularly for topographical and control surveys. Plane table surveying is simple, accurate, cost-effective, and suitable for rough and inaccessible terrain. In this article, we will discuss the methods involved in plane table surveying.

1. Orientation:
Orientation refers to the process of aligning the table in a true north-south direction. This is achieved by using a magnetic compass or a theodolite. The compass or the theodolite is placed on the table’s edge, and the table is tilted until the needle or the vertical hair is aligned with the north-south direction. This process is repeated at different stations to ensure accuracy.

2. Station Setup:
After orientation, the table is set up at a known point or station. The location of this station is determined using a survey mark, such as a benchmark or a permanent monument. A minimum of three stations are required to plot a point using the plane table method.

Radiation method is used to plot or measure points on a plane table. This method involves measuring distances from the known station to the new point using a tape or chain. The table’s edge is then aligned with the line joining the known station and the point, and the table is pivoted until the new point is seen through the alidade. The new point is then plotted on the table’s surface.

4. Intersection Method:
The intersection method is similar to the radiation method, except that it requires a minimum of two known stations. The table is set up at one of the known stations, and the position of the other station is plotted using the alidade and a sighting rod. A line is then drawn on the table connecting the two known stations. This process is repeated for other points, and their intersections give the plotted positions.

5. Traversing Method:
Traversing method is used to survey large areas and requires at least three known stations. A traverse is a series of connected lines that represent the boundary of an area to be surveyed. The table is set up at the first known station, and the line connecting it to the next station is drawn on the table. The table is then moved to the next station, and the process is repeated until all the points are connected.

6. Resection Method:
Resection method is used to determine the location of an unmarked point by sighting back to two or more known points. The table is set up at the point whose location is to be determined, and an alidade is used to sight back to the known points. The table is then pivoted until the lines of sight from the known points intersect on the table’s surface, giving the position of the unknown point.

In conclusion, plane table surveying is an efficient and accurate method for measuring horizontal distances and angles. It is widely used in small-scale surveys, and the various methods mentioned above can be used depending on the survey’s requirements. The simplicity and cost-effectiveness of plane table surveying make it a popular choice among civil engineers and surveyors.

## Advantages of Plane Table Surveying

Plane table surveying is a type of surveying where a flat table or board is used as the main equipment for measuring and drawing the features of a land or area. It is a commonly used technique in civil engineering and offers several advantages over other surveying methods. Some of the main advantages of using plane table surveying are as follows:

1. Simplicity and portability: Plane table surveying is a simple and portable method of surveying, making it suitable for both large and small-scale projects. The plane table and its accessories can be easily carried to the site, making it a convenient option for surveyors.

2. Cost-effective: Compared to other surveying methods, plane table surveying is relatively inexpensive. The equipment required, including the table, is affordable, and the survey can be completed with limited manpower, saving on labor costs.

3. Direct and accurate measurements: Plane table surveying directly measures the features of the land or area. The measurements are taken directly from the plane table, eliminating the need for complex calculations and reducing the chances of errors. This results in accurate and reliable data.

4. Quick and efficient: Plane table surveying is a quick and efficient method of surveying. The measurements are taken on-site and plotted on the table itself, eliminating the need for additional processing time. This enables surveyors to complete the survey in a shorter amount of time, making it a preferred method for time-sensitive projects.

5. Suitable for uneven terrain: Unlike other surveying techniques that may require specialized equipment to measure uneven terrain, plane table surveying can be easily adapted to suit any type of terrain. The plane table can be leveled precisely, making it possible to obtain accurate measurements even on uneven surfaces.

6. Ideal for small-scale projects: Plane table surveying is particularly suitable for small-scale projects, such as residential properties or small land developments. It is a cost-effective method that provides reliable data for these types of projects.

7. Unlimited visual range: As the plane table is a flat surface, it offers an unlimited visual range. This means that surveyors can cover a large area in a single survey, reducing the need for multiple setups and allowing for a more comprehensive analysis of the area.

In conclusion, plane table surveying offers numerous advantages for civil engineers, making it a popular and widely used method for surveying. Its simplicity, cost-effectiveness, accuracy, and suitability for various terrains and project sizes make it a valuable tool for any surveying project.

## Conclusion

In summary, the introduction of plane table surveying has greatly revolutionized the field of land surveying. This method has provided surveyors with a more efficient and accurate way of collecting and recording data, enabling them to produce more precise maps and plans. By eliminating the need for complex instruments and equipment, plane table surveying has also made surveying more accessible and cost-effective. However, proper training and skill development are necessary for conducting plane table surveying effectively. With continuous advancements and integration of technology, plane table surveying is expected to continue playing a vital role in land surveying for years to come. As such, understanding the fundamentals of this method and incorporating it into modern surveying techniques is crucial for any surveyor seeking to thrive in the