Ranging (Direct & Indirect), Principle of Chain Survey and Applications

Ranging and chain surveying are fundamental concepts in the field of surveying. They are widely used for measuring distances and establishing straight lines between points on the ground. For students of the Surveyor trade, understanding ranging methods, principles of chain surveying, and their applications is essential for accurate fieldwork and map preparation.

Ranging

Ranging is the process of establishing intermediate points on a straight line between two end points. It ensures that the survey line is straight and measurements are taken accurately along that line.

Ranging is necessary when the distance between two points is long or when obstacles make it difficult to measure directly. It helps in maintaining alignment during chain surveying.

Types of Ranging

1. Direct Ranging

Direct ranging is used when the two end points are intervisible, meaning they can be seen from each other. In this method, intermediate points are located visually along the straight line joining the two end points.

Procedure:

• Place ranging rods at the two end points
• The surveyor stands behind one rod and directs an assistant
• The assistant moves the rod until it appears in line with the two end points
• This process is repeated to fix all intermediate points

Direct ranging is simple, quick, and commonly used in open areas where visibility is clear.

2. Indirect Ranging

Indirect ranging is used when the two end points are not intervisible due to obstacles such as hills, buildings, or trees. In this method, intermediate points are established using indirect methods.

There are two common methods of indirect ranging:

a) Reciprocal Ranging

This method is used when both end points are not visible to each other due to rising ground or obstruction. Two surveyors stand at intermediate points and guide each other to align properly.

b) Random Line Method

In this method, a random line is drawn, and offsets are measured to establish the correct alignment.

Indirect ranging requires more time and skill but is essential in difficult terrain.

Principle of Chain Survey

Chain surveying is the simplest method of surveying in which only linear measurements are taken using a chain or tape. It is based on the principle of dividing the area into a network of triangles.

The main principle of chain surveying is:

• To divide the survey area into well-conditioned triangles

A well-conditioned triangle is one in which no angle is too small or too large, ensuring accuracy in plotting.

By measuring the sides of these triangles, the entire area can be plotted accurately on a drawing sheet.

Features of Chain Survey

• Only linear measurements are taken
• No angular measurements are required
• Suitable for small and simple areas
• Easy to perform and economical

Steps in Chain Survey

1. Reconnaissance (initial inspection of the area)
2. Selection of survey stations
3. Ranging of survey lines
4. Measurement of distances using chain or tape
5. Taking offsets to locate details
6. Recording data in field book
7. Plotting the survey on drawing sheet

Applications of Ranging and Chain Survey

Ranging and chain surveying are widely used in various fields:

1. Small Area Surveys

Chain surveying is suitable for small areas with simple details, such as agricultural land or small plots.

2. Construction Work

Ranging is used to establish straight lines for construction of roads, buildings, and boundaries.

3. Land Measurement

Used for measuring land boundaries and preparing layout plans.

4. Preliminary Surveys

Chain surveying is often used for initial surveys before detailed surveying is carried out.

5. Educational Purposes

It is widely used in training and education to teach basic surveying techniques.

Advantages of Chain Survey

• Simple and easy to use
• Requires less equipment
• Economical method
• Suitable for beginners

Limitations of Chain Survey

• Not suitable for large or complex areas
• Less accurate compared to modern methods
• Difficult to use in rough or obstructed terrain

Precautions in Ranging and Chain Survey

• Ensure proper alignment of ranging rods
• Use clear and visible signals
• Avoid errors in measurement
• Maintain straight survey lines
• Record data accurately

Importance in Surveyor Trade

Ranging and chain surveying form the foundation of surveying practices. They help students understand basic concepts of measurement, alignment, and plotting.

Mastering these techniques is essential before learning advanced surveying methods. It builds confidence and improves accuracy in fieldwork.

Conclusion

Ranging and chain surveying are essential techniques used in surveying for establishing straight lines and measuring distances. Direct and indirect ranging methods help in maintaining alignment under different conditions.

The principle of chain surveying, based on triangulation, ensures accurate representation of areas. These methods are widely used in small-scale surveys and training.

For ITI Surveyor trainees, understanding these concepts is crucial for developing strong fundamentals and achieving success in the field of surveying.