Chain Survey – Classification, Accuracy and Types
Chain surveying is one of the simplest methods of surveying, mainly used for measuring distances on the ground. In ITI Draughtsman Civil, it is important to understand the classification of surveying methods, the level of accuracy required, and the different types of chain surveying used in practice.
1. Classification of Surveying
Surveying can be classified in different ways based on the nature of the work and methods used.
(a) Based on Curvature of Earth
- Plane Surveying: Assumes the earth surface as flat. Suitable for small areas and commonly used in chain surveying.
- Geodetic Surveying: Considers the curvature of the earth. Used for large areas and high accuracy work.
(b) Based on Instruments Used
- Chain Survey
- Compass Survey
- Plane Table Survey
- Theodolite Survey
- Levelling
(c) Based on Purpose
- Topographical Survey: Shows natural and artificial features.
- Cadastral Survey: Used for land records and boundaries.
- Engineering Survey: Used for construction projects.
2. Accuracy in Chain Survey
Accuracy refers to how close the measured values are to the true values. In chain surveying, accuracy depends on proper use of instruments, skill of the surveyor, and field conditions.
Factors Affecting Accuracy
- Condition and calibration of chain or tape.
- Skill and experience of the surveyor.
- Proper ranging and alignment.
- Temperature and weather conditions.
- Nature of ground (level or uneven).
Methods to Improve Accuracy
- Use of well-conditioned triangles.
- Providing check lines for verification.
- Taking repeated measurements.
- Ensuring proper handling of instruments.
Although chain surveying is less accurate compared to modern methods, it provides sufficient accuracy for small-scale works.
3. Types of Chain Survey
Chain surveying can be classified into different types based on the complexity of the area and method of measurement.
(a) Simple Chain Survey
- Used for small, open, and level areas.
- Consists of simple triangular framework.
- Suitable for fields and small plots.
(b) Compound Chain Survey
- Used for larger areas with more details.
- Includes several triangles connected together.
- Requires careful planning and measurement.
(c) Chain Survey with Offsets
- Used when objects are not directly on the chain line.
- Offsets are taken to locate such features.
- Includes perpendicular and oblique offsets.
(d) Chain Survey with Tie Lines
- Uses tie lines to locate interior details.
- Improves accuracy and completeness of survey.
4. Importance of Classification and Accuracy
- Helps in selecting the appropriate method of surveying.
- Ensures reliable and accurate data collection.
- Reduces errors in mapping and construction.
- Improves efficiency of survey work.
Role of Draughtsman Civil
A Draughtsman Civil uses survey data to prepare plans and layouts. Understanding classification, accuracy, and types of chain survey helps in interpreting field data correctly and producing precise drawings.
Conclusion
Chain surveying is classified based on method, purpose, and area of work. Accuracy plays an important role in obtaining reliable results. Different types of chain survey are used depending on the complexity of the area.
For ITI Draughtsman Civil students, knowledge of classification, accuracy, and types of chain survey is essential for effective surveying and construction planning.