Compass surveying is generally adopted for angular measurements and linear measurements, for determining the location of particular objects. Here the liner or horizontal measurements are measured with the use of a chain survey; the chain survey can be used when the survey area is too small and flat.
For compass surveying, the compass is the main instrument. It is one type of small surveying instrument with a magnetic needle and graduated circle and line of sign. The compass instrument consists of a cylindrical metal box with a top glass cover and its diameter is 8 to 12 cm.
Read More: 10 Types of Land Survey | What Is Land Surveying
Principle of Compass Surveying
The principle of a survey is traversing, which consists of a series of connected lines the bearing of the lines is measured by a prismatic compass and the linear dimensions are measured by a chain survey.
This compass survey does not require any formulation of a triangle network and this compass survey is suitable for large areas, full of many details and undulating.
The Compass survey is not suitable for those areas where the local attraction is suspected due to the presence of magnetic substances like iron ore deposits, electric cables, steel structures, and many more.
Types of Compass Surveying
The following types of compass surveying,
- Prismatic Compass
- Surveyor Compass
- Level Compass
Here, explained the types of compass briefly,
Prismatic Compass
The Prismatic Compass was invented by Charles and painted in 1812. The Prismatic compass is a surveying instrument, which is used to determine an angle between transverse, direction, and waypoint.
As the name suggests, a prismatic compass has a prism for taking observation and reading preciously. Also, prismatic compasses are portable magnetic compasses that can be either used as a fit on the tripod stand or hand instrument. A prismatic compass can be taking a reading and sighting at the same time, without changing the position.
The Least Count Reading of the Prismatic Compass is 30 minutes (30’), also the prismatic compass follows the Whole circle Bearing system ( 0 to 360 degrees) for finding the Angle.
The Prismatic Compass is light in weight so that easy to carry and more workable. The main point kept in mind while carrying out a survey is, to avoid local attraction or free rotation of the magnetic needle of the compass.
Read More: What Is Chain Surveying | Principles Of Chain Surveying | Chaining In Surveying
Instrument Used for taking a Prismatic Compass Surveying,
- Field Book
- Plumb bob
- Ranging Rod
- Arrow
- Tripod Stand
- Measuring Tape
Parts of Prismatic Compass
Here the major parts of the prismatic compass are listed,
- Magnetic needle
- Graduated ring
- Adjustable mirror
- Sliding arrangement for mirror
- Object vane
- Eye vane
- Pivot
- Lifting Pin
- Prism
- Spring Break
- Metal box
- Glass cover
- Horsehair
Errors in Prismatic Sources
- Improper Leveling of the compass on the tripod Stand.
- Improper Centering of the compass.
- Local Attraction means when magnetic objects are available nearby the compass, then it affects the property of magnetic of the Prismatic Compass.
Surveyor Compass
Surveyor Compass is the same as the prismatic compass but the only difference is it uses a quadrant bearing method (0 to 90 degrees) for taking an observation reading.
The Surveyor compass has plain eye silt instead of the prismatic compass; prismatic compasses have an eye hole and eye slit with a prism. The surveyor compasses have a magnetic pointed needle instead of a broad needle.
Working of Surveyor Compass
- Centering
- Leveling
- Observe the bearing
Advantages of Compass Survey
- A compass survey is suitable for retracing the old survey.
- The compass survey instrument is lightweight and portable, so easy to carry with a tripod stand.
- In the compass survey, the instrument is easy to set up.
- An error in the single-line survey does not affect the other survey line.
Disadvantages of Compass survey
- Improper sighting of the ranging rod, a high chance of getting errors.
- Compass surveys are subjected to several types o errors like local attraction, magnetic meridian, etc.
- A compass survey is less precise as compared to advanced survey techniques.
- A compass survey is a tedious process.
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