Introduction To Compass Surveying
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 to be small and flat.
For compass surveying, the compass is the main instrument. It is one type of small surveying instrument with having 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.
In the exact centre of the compass, one magnetic needle is fixed, which is attached to the graduated aluminium ring. The prism helps to read reflect and easy to read out the reading on the graduated ring.
An opposite of the prism, the object vane is having horsehair which is help to bisect an object. If the survey area is large, crowded with details, undulated then the principle of chainage survey is not applicable. In that case, the traversing method is used for the survey.
Principle of Compass Surveying
The principle of a survey is traversing, that is consisting 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 Survey
The following types of compass surveys,
- Prismatic Compass
- Surveyor Compass
- Level Compass
Here, explained the types of compass briefly,
Prismatic Compass was invented by Charles and panted 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 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 is kept in mind while carrying out a survey is, to avoid local attraction or free rotation of the magnetic needle of the compass.
Instrument Used for taking a Prismatic Compass Surveying,
- Field Book
- Plumb bob
- Ranging Rod
- 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
- Lifting Pin
- Spring Break
- Metal box
- Glass cover
- Horse hair
Errors in Prismatic Sources
- Improper Leveling of the compass on the tripod Stand.
- Improper Centering of the compass.
- Local Attraction means when the magnetic objects are available nearby the compass, then it affects the property of magnetic of the Prismatic 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.
Surveyor compass has plain eye silt instead of the prismatic compass; prismatic compasses have an eye hole and eye slit with prism. The surveyor compasses have a magnetic pointed needle instead of a broad needle.
Working of Surveyor Compass
- Observe the bearing
Advantages of Compass Survey
- 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 compass survey, the instrument is easy to set up.
- An error of single line survey does not affect the other survey line.
Disadvantages of Compass survey
- Improper sighting of the ranging rod, high chance of getting error.
- Compass surveys are subjected to several types o error like local attraction, magnetic meridian, etc.
- Compass survey is less precise as compared to advance survey techniques.
- Compass survey is a tedious process.
What is a Principle of Compass Surveying?
The principle of a survey is traversing, that is consisting 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. As the name suggests, a prismatic compass has a prism for taking observation reading preciously. Also, prismatic compasses are portable magnetic compasses that can be either used as a fit on the tripod stand or hand instrument.
Which is the type of Compass Survey?
The following types of compass surveys,
What are the Advantages of Compass Survey?
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 compass survey, the instrument is easy to set up.
An error in a single line survey does not affect the other survey line.
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