What is Chain surveying?
Chain surveying is a fundamental method in land surveying that involves measuring distances and angles to determine the relative positions of points on the ground. This technique is particularly useful for small areas where accuracy is vital and can be executed using various methods and tools. The following overview covers methods of linear measurement, types of chains and tapes, ranging techniques, chaining on sloping terrain, chain triangulation, survey lines, offsets, obstacles encountered during chaining, and the plotting process.
Chain surveying is a land surveying method that involves measuring distances and angles to determine the relative positions of points on the ground, primarily used for small areas where accuracy is important.
Table of Contents
Methods of Linear Measurement
The methods of linear measurement of chain survey involves
Pacing
Pacing is a quick method of measuring distance by counting the number of steps taken. Typically, a standard pace measures around 0.8 to 1 meter, depending on the person’s stride. While pacing is efficient for rough estimates, it lacks the precision necessary for detailed surveys.
Mileage
This method is mainly used in road surveying, where distances are measured in miles or kilometers using a calibrated wheel, often called a surveyor’s wheel. This wheel rolls over the ground and records the distance traveled, making it effective for longer distances with reasonable accuracy.
Recorder
This measurement technique can involve electronic devices that automatically record distances as the surveyor moves. Electronic Distance Measuring (EDM) tools utilize laser technology to provide precise measurements, simplifying the process and enhancing accuracy, especially over extended distances.
Taping
Taping is one of the most accurate linear measurement methods. It uses a marked steel or cloth tape to directly measure distances. Steel tapes are preferred for their durability and precision, measuring in meters or feet. The tape is pulled tight between two points, and the distance is read directly, making it essential for precise surveying.
Types of Chains and Tapes
Chains
The most common type is the Gunter’s chain, measuring 66 feet long and consisting of 100 links, primarily used in agricultural surveys. Another type is the engineer’s chain, which is often 100 feet long and utilized in engineering projects. Chains are robust and resistant to stretching but can be affected by temperature variations.
Tapes
Tapes are typically made of steel, fiberglass, or cloth. Steel tapes offer high accuracy and longevity, while fiberglass tapes are lightweight and rust-resistant, making them suitable for outdoor use. Cloth tapes are flexible and often used for rough measurements. Tapes are usually marked in both metric and imperial units for versatility.
Ranging: Direct and Indirect
Direct Ranging
This technique in chain survey involves placing markers (such as pegs) in a straight line between two points. The surveyor aligns visually with a marker at the opposite end. This method works well for short distances and provides a clear line of sight.
Indirect Ranging
When direct sight is blocked, indirect ranging is employed. It uses a third point to create a triangle, allowing the surveyor to visualize alignment indirectly. Tools like a compass or theodolite help establish angles and determine the correct line between the initial points.
Chaining on Sloping Ground
When chaining on inclined surfaces, it is crucial to consider the slope’s angle for accurate measurements. Techniques to achieve this include:
Horizontal Measurement
Using a level to establish a horizontal line from the starting point, allowing the surveyor to measure distances horizontally rather than along the slope.
Slope Correction
If the slope angle is known, a correction factor can be applied to adjust the measurement. This often involves using trigonometric calculations to convert slope distance into horizontal distance.
Chain Triangulation
Chain triangulation is a method that uses triangles to determine the locations of points. By measuring the lengths of the triangle’s sides and knowing one angle, surveyors can calculate the other angles and sides using trigonometry. This approach is useful for establishing control points and is commonly employed in mapping and property surveys. Triangulation ensures accuracy over larger areas by allowing surveyors to calculate positions from known points.
Survey Lines
Survey lines are the straight lines drawn between survey points, forming the foundation for all measurements and observations during the survey. Proper establishment of survey lines is essential for accuracy, considering factors such as:
Straightness: Ensuring lines are straight minimizes measurement errors.
Visibility: Lines should be visible from each point to maintain alignment.
Marking: Clearly marking each survey point with stakes or flags helps avoid confusion.
Offsets
Offsets are used to measure distances from a survey line to specific points or features, such as trees or buildings. This technique is critical when obstacles obstruct direct measurements. Offsets enable surveyors to maintain accuracy while mapping areas surrounding the primary survey line. Common types of offsets include:
- Perpendicular Offsets: Measuring directly at a right angle to the survey line to locate features.
- Angular Offsets: Measuring at an angle to the survey line to account for obstacles.
Obstacles in Chaining
Obstacles can complicate accurate chaining measurements. Common challenges include:
Vegetation: Trees and dense brush can obstruct sight lines.
Terrain: Hills, ditches, or irregular ground can make measurements difficult.
Structures: Buildings or fences may block direct access to measurement points.
To navigate these obstacles, surveyors may use techniques like indirect ranging, establishing offsets, or repositioning survey points to ensure a clear line of sight.
Plotting
Plotting in chain surveying involves creating a plan or map based on the measurements and observations from the survey. The process includes several steps:
Data Collection: All measurements, angles, and distances recorded during the survey are compiled.
Coordinate System: Establishing a coordinate system is vital for accurate plotting, which can be based on local grids or geographic coordinates.
Drawing: Using drafting tools or software, surveyors plot the points according to their recorded measurements, creating a visual representation of the surveyed area.
Scale: Ensuring the plot is to scale is essential for an accurate representation, with the scale depending on the level of detail required and the surveyed area.
Final Review: After plotting, surveyors review the map for accuracy, ensuring all points are correctly represented and labeled.
Conclusion
Chain surveying is an essential technique in land surveying that employs various methods for linear measurement and utilizes tools such as chains and tapes. Understanding techniques for ranging, chaining on slopes, triangulation, and plotting enables surveyors to accurately assess land and define clear boundaries and features. Mastery of these principles is crucial for effective land management and development, highlighting the importance of chain surveying as a vital skill in the field.
Frequently Asked Questions (FAQ)
What is chain surveying?
Chain surveying is a land surveying method that involves measuring distances and angles to determine the relative positions of points on the ground, primarily used for small areas where accuracy is important.
How is plotting done in chain surveying?
Plotting in chain surveying involves creating a map based on recorded measurements. This includes data collection, establishing a coordinate system, drawing points to scale, and reviewing the map for accuracy.
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