Exploring the Fundamentals of Plane Table Surveying: Methods, Equipment, Errors, Advantages, and Limitations
Plane table surveying is an old method of mapping and land surveying. It entails the use of a specifically built table known as a plane table, as well as a range of tools and procedures. In this article, we will look at the fundamentals of plane table surveying, such as the procedures utilised, the equipment used, the mistakes that can occur, and the benefits, drawbacks, and limits of this surveying methodology.
What are the Methods of Plane Table Surveying?
Plane table surveying employs several methods to accurately measure and map an area. The main methods used in plane table surveying are:
1. Radiation Method: The radiation method involves selecting a point on the ground and aligning the plane table towards it. The surveyor fixes the plane table at this reference point and then locates and marks other points by sighting them with a surveying compass. The angles and distances between the reference point and the other points are measured using the alidade and surveying compass.
2. Intersection Method: In the intersection method, the surveyor locates points by measuring angles and distances from two or more known reference points. The surveyor sets up the plane table at one reference point and sights another reference point using the alidade. The line of sight to the second reference point is marked on the plane table. Then, the process is repeated with another reference point. The intersection of the marked lines on the plane table represents the position of the desired point.
3. Traversing Method: Traversing is a method used to establish control points and measure distances and angles between them. It involves a sequence of interconnected lines forming a closed polygon. The surveyor starts by setting up the plane table at a known control point. The alidade is used to measure angles and distances to the next control point. The surveyor then moves to the next control point and repeats the process until the polygon is completed. By measuring and recording the angles and distances, the surveyor can determine the positions of all the control points.
These methods provide different approaches to measuring and locating points on the ground using a plane table. Depending on the specific requirements of the survey and the nature of the terrain, surveyors may choose the most suitable method or a combination of methods to achieve accurate and reliable results.
What are the Equipments Used in Plane Table Surveying?
Plane table surveying requires specific equipment to carry out the surveying tasks. The essential equipment used in plane table surveying includes:
1. Plane Table: The plane table is the central piece of equipment in plane table surveying. It is a flat, level surface mounted on a tripod. The plane table provides a stable platform on which the surveyor can make measurements, draw sketches, and record data during the survey.
2. Alidade: The alidade is a sighting device that is attached to the plane table. In this case, it is a straight edge or ruler with a telescopic sight attached to it. The alidade allows the surveyor to sight distant objects accurately and measure angles between points.
3. Surveying Compass: A surveying compass is an essential tool used in plane table surveying. It is used to measure angles and bearings. The compass provides the surveyor with information about the direction of lines and helps establish reference points.
4. Ranging Rod: A ranging rod, also known as a ranging pole or ranging staff, is used to measure distances during plane table surveying. It is a long, slender pole made of wood or metal, typically marked with measurements. The ranging rod is placed at specific points on the ground, and the surveyor reads the distance from the plane table to the ranging rod using the alidade.
5. Drawing Equipment: Various drawing tools and equipment are used to record and sketch the survey measurements on the plane table. These may include pencils, pens, rulers, protractors, graph paper, and other stationery items necessary for drawing accurate diagrams and maps.
6. Tripod: A sturdy tripod is used to support and stabilize the plane table. The tripod ensures that the plane table remains level and secure during the survey, allowing for precise measurements and drawings.
7. Measurement Tape: A measurement tape or measuring chain may be used to measure longer distances during plane table surveying. It is used in conjunction with the ranging rod to measure distances accurately.
Limitations of Plane Table Surveying
The precision of the plane table, the alidade, and the surveyor are the limits of plane table surveying. The precision of the plane table may be increased by utilising a high-quality plane table and properly levelling it.
Using a high-quality alidade and precisely seeing the points can increase alidade accuracy. The surveyor's accuracy can be enhanced by educating him or her and employing a range of error-reduction tactics.
Advantages and Disadvantages of Plane Table Surveying
Plane table surveying, like any surveying method, has its own set of advantages and disadvantages. Let's explore them below:
Advantages of Plane Table Surveying
1. Simplicity: Plane table surveying is relatively simple to understand and implement. It does not require complex equipment or advanced technical knowledge, making it accessible to surveyors with varying levels of experience.
2. Real-time Data: One significant advantage of plane table surveying is that it provides immediate results. Surveyors can observe and make adjustments on-site, allowing for real-time data collection and analysis. This can be particularly useful in situations where quick decisions or modifications are necessary.
3. Flexibility: Plane table surveying is versatile and can be applied to a wide range of surveying tasks. It can be used for topographic mapping, boundary surveys, construction layout, and other types of land surveying projects. This adaptability makes it a valuable tool in the surveyor's toolkit.
4. Cost-Effective: Compared to some modern surveying techniques that require expensive equipment or specialized software, plane table surveying can be a cost-effective option. The equipment required for plane table surveying is relatively simple and typically more affordable, which can be beneficial for smaller-scale projects with budget constraints.
Disadvantages of Plane Table Surveying
1. Time-Consuming: Plane table surveying can be time-consuming, particularly for large areas or complex terrains. It involves manual plotting and measurement of points, which can be labour-intensive and require significant time and effort. This can limit its practicality for projects with tight schedules or where efficiency is paramount.
2. Limited Accuracy: Compared to modern surveying techniques such as Global Positioning System (GPS), plane table surveying has limitations in terms of accuracy. Errors can arise due to human measurement errors, environmental factors, or the limitations of the equipment used. This makes it less suitable for surveys that require a high degree of precision or where accurate geospatial data is crucial.
3. Vulnerability to Environmental Factors: Plane table surveying is susceptible to environmental factors that can affect the stability of the equipment and the accuracy of measurements. Wind, temperature changes, vibrations, and other natural elements can introduce errors in the survey. This requires surveyors to be mindful of these factors and take appropriate precautions during the survey.
4. Limited Range: Plane table surveying is generally effective for small to medium-sized areas. For large-scale surveys or projects covering extensive territories, the limitations of plane table surveying, such as time consumption and limited accuracy over long distances, may pose challenges. In such cases, more advanced surveying techniques may be more suitable.
Plane table surveying is a significant technique that has been used in land surveying for millennia. Surveyors may make educated judgements about when and how to use this approach by knowing its procedures, equipment, mistakes, advantages, downsides, and restrictions.
While plane table surveying may not be appropriate in every case, its ease of use, real-time data availability, and versatility make it a feasible alternative for a variety of surveying activities.
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However, it is critical to examine the potential flaws and limits of this approach, as well as advances in current surveying technology. Surveyors can obtain precise and efficient outcomes in their mapping and land surveying endeavours by combining old and new methodologies.