What are the different types of compasses used in surveying?

Short Answer:

The different types of compasses used in surveying include the prismatic compass, surveyors compass, lensatic compass, and gyro compass. These instruments are used to measure bearings and directions with respect to the magnetic north. Each type has unique features and is suitable for specific survey needs.

A prismatic compass is commonly used in field surveys for accurate readings, while a surveyor’s compass is useful in plotting bearings. The lensatic compass is often used for quick military-style navigation, and the gyro compass is ideal for finding true north in areas where magnetic disturbances exist.

Detailed Explanation:

Different types of compasses used in surveying

In surveying, a compass is a simple but essential instrument used to measure directions or bearings between two points. It helps surveyors determine the orientation of lines relative to the magnetic north. Depending on the survey’s accuracy and purpose, different types of compasses are chosen. Each compass functions slightly differently but aims to provide directional data to support land measurement and mapping.

1. Prismatic Compass

This is one of the most widely used compasses in surveying. It includes a magnetic needle that aligns with the earth’s magnetic field, and a prism to read the bearing while sighting the object.

Features:

  • Measures magnetic bearings.
  • Readings can be taken while sighting the object.
  • Graduated in whole circle bearing (0°–360°).
  • Suitable for medium-accuracy surveys.

2. Surveyor’s Compass

Also known as the circumferentor, this compass measures the horizontal angle between two points. It has a magnetic needle and is often mounted on a tripod.

Features:

  • Measures bearings in quadrantal form (0°–90° in each quadrant).
  • Used in chain surveying or traverse surveys.
  • Suitable for land boundary marking and preliminary work.

3. Lensatic Compass

Commonly used in military and navigation, this compass is portable and easy to use. It includes a magnifying lens for clear reading.

Features:

  • Quick field orientation.
  • Not as precise as prismatic or surveyor’s compass.
  • Often used in rough terrain for basic direction finding.

4. Gyro Compass

Unlike magnetic compasses, the gyro compass points to true north using the principles of a gyroscope. It is less affected by nearby metal objects or magnetic interference.

Features:

  • Used where high precision is needed.
  • Suitable in areas with magnetic disturbances.
  • Common in maritime and tunnel surveying.

Use of Compasses in Surveying

Compasses are mainly used to:

  • Determine the direction of survey lines.
  • Record field observations.
  • Plot rough maps and layouts.
  • Assist in traverse and preliminary surveys.

They are especially useful in areas with limited visibility or access, where high-tech equipment may not be practical.

Conclusion

The different types of compasses used in surveying—prismatic, surveyor’s, lensatic, and gyro compasses—are chosen based on the purpose, terrain, and required accuracy of the survey. These instruments help in determining bearings and ensuring proper alignment of survey lines, making them a valuable part of basic surveying tools.