WHAT IS MERIDIAN
Meridian is the line of reference from which the bearing of the line is measured. There are three types of meridian. OR The imaginary vertical plane passing through the magnetic axis of the geomagnetic is called the magnetic meridian.
- True meridian
- Magnetic meridian
- Arbitrary meridian
WHAT IS THE MAGNETIC MERIDIAN
Magnetic meridian. The direction indicated by freely suspended and properly balanced magnetic needle, unaffected by local attraction force is called magnetic meridian, and the horizontal angle made with the object or line is called magnetic bearing. It is expressed in degrees minutes and seconds, to showing the magnetic meridian which device is called the magnetic compass. The other method is also used for showing magnetic meridians like gyroscopes, magnetometers, and GPS receivers.
The compass consists of (i) A magnetic needle (ii) A graduated circle (iii) A line of sight
There are three types of compass in common use.
1. The prismatic Compass:- The prismatic Compass may be held in the hand, but for better result, it is usually mounted on a light striped which carries a verticle spindle in the ball and socket joint to which the box is screwed. By means of this arrangement, the instrument can be quickly leveled and also rotated in a horizontal plane and clamped in any position.
2. Surveying Compass or Surveyor's Compass:-
The Surveyor's Compass was formerly much used in land surveying, but now it is little used.
The main difference between prismatic compass and surveying compass is east and west quadrants to reverse to each other.
The nature of has magnetic needle is aligned with the local magnetic meridian, then It is of great use in engineering for directional purposes. It is also used for finding the difference between the true meridian and magnetic meridian in surveying and mapping.
Use of magnetic meridian
1. To find the true meridian:- If you want true meridian or true north of a point then easily determined the true meridian by the use of magnetic declination which is given on the map.
2. For finding bearing of line:- If you want magnetic bearing of a line. the easily determined the bearing of line.
3. In underground mine surveying where the GPS is not working properly.
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