Types of Compass
Understanding different types of compasses used in surveying and civil engineering applications.
Introduction
A compass is one of the fundamental instruments used in surveying for measuring the direction of survey lines with respect to the magnetic meridian. It helps surveyors determine bearings and perform traversing operations accurately.
Different types of compasses are used depending on the accuracy required, field conditions, and surveying applications.
The main types of compasses used in surveying are:
- Trough Compass
- Tubular Compass
- Prismatic Compass
- Surveyor’s Compass
Trough Compass
A trough compass is a simple magnetic compass generally used for determining magnetic north and rough directions in surveying works.
Characteristics
- Simple construction
- Rectangular or trough-shaped body
- Portable and lightweight
- Used mainly for orientation purposes
Applications
- Plane table surveying
- Preliminary field orientation
- Educational and training purposes
Tubular Compass
A tubular compass consists of a magnetic needle enclosed within a cylindrical or tubular casing for protection and improved portability.
Characteristics
- Compact and portable instrument
- Protective tubular casing
- Provides quick directional readings
- Easy to carry during fieldwork
Applications
- Reconnaissance surveys
- Forest surveying
- Military and navigation purposes
Prismatic Compass
The prismatic compass is one of the most commonly used surveying compasses for measuring whole circle bearings.
Characteristics
- Measures Whole Circle Bearings (WCB)
- Uses a prism for reading observations
- Graduated ring attached to magnetic needle
- Provides comparatively high accuracy
- Can be hand-held or tripod mounted
Applications
- Traverse surveying
- Route surveys
- Engineering surveys
- Topographical surveys
Main Feature: Simultaneous sighting and reading through a prism.
Surveyor’s Compass
A surveyor’s compass is used for measuring reduced or quadrantal bearings in surveying operations.
Characteristics
- Measures Quadrantal Bearings (QB)
- Graduated ring fixed to the compass box
- Magnetic needle moves independently
- Suitable for ordinary surveying works
Applications
- Compass traversing
- Boundary surveys
- Small engineering projects
Main Feature: Measures Reduced Bearings (Quadrantal Bearings).
Comparison of Different Types of Compass
| Type of Compass | Bearing System | Accuracy | Main Use |
|---|---|---|---|
| Trough Compass | Approximate Direction | Low | Orientation |
| Tubular Compass | Directional Reading | Moderate | Reconnaissance |
| Prismatic Compass | Whole Circle Bearing | High | Traverse Survey |
| Surveyor’s Compass | Quadrantal Bearing | Moderate | Boundary Survey |
Importance of Compass in Surveying
- Determination of magnetic bearings
- Traverse surveying operations
- Boundary and route surveys
- Direction finding and orientation
- Preliminary reconnaissance surveys
Conclusion
Different types of compasses are used in surveying depending on the required accuracy and field application. Trough and tubular compasses are mainly used for orientation and reconnaissance, while prismatic and surveyor’s compasses are widely used for accurate bearing measurements in engineering surveys.
Understanding the characteristics and applications of each type of compass helps surveyors choose the most suitable instrument for field operations.
Author
Mohan Dangi (Gold Medalist)
Civil Engineer | Geotechnical Engineer
References
- B.C. Punmia – Surveying Volume I
- S.K. Duggal – Surveying
- R. Agor – Surveying and Levelling
- Standard Civil Engineering Surveying Manuals
- IS Codes Related to Surveying Practices
Disclaimer
This article is intended for educational and informational purposes only. Instrument specifications, surveying procedures, and field applications may vary depending on equipment manufacturers, project requirements, and applicable engineering standards. Readers are advised to consult professional surveying references and guidelines before applying these concepts in practical fieldwork.
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