Compass Survey | index survey | what is compass survey | diksoochak sarvekshan

Compass Survey

Compass Survey) : When the angles (along with the length) are measured to find the direction and horizontal position of the survey lines in the area, it is called directional survey. The direction (angle) is taken with reference to the meridian or any other line.

 Keep in mind, the length of the survey lines is measured with the help of jarib and lace, just like in the survey. , When the land area is small and open and it is possible to divide it in the structure of shaped triangles, then it is appropriate to adopt the Zarib survey.

If the land area is very large and densely populated and due to being surrounded by buildings or other obstacles, it is difficult to insert triangles, coincidences and check lines (necessary for poor survey), then directional survey is suitable for such area.

In directional survey, survey lines encircling the land area and adjacent to each other in sequence are taken. The length of these lines is measured with a jarib/lace (like a jarib survey) and the direction is determined by an angle measuring instrument. Knowing the length of the lines and the angle between them, the shape of the land can be easily drawn on the drawing sheet. There is no need to divide the area into a network of triangles.

There are many instruments available to measure the direction of survey lines, but in this type of survey, compass is used, which is a simple type of instrument. Hence it has been named as Compass Survey.

       This survey is also called a traverse survey, because the whole area is threaded like a garland in a fixed circle by survey lines adjacent to each other. In chankram survey, there is no need to put baseline, coincidence lines, check lines etc. on the area.

  (Compass)

Magnetic compass is used to measure the magnetic field of survey lines. These are measured in quadrant or full circle method.

On this basis the following two types of indicators have been made.

(i)  Surveyor Compass)

(ii) Prismatic Compass)

 Earlier surveyor's compass was more useful in earth survey, but now the use of prismatic compass is more. The level instrument is also fitted with a prismatic type of compass, but the function of visual acuity is taken by binoculars.

 Apart from these, there is another compass, the Trough Compass, which does not measure angular, only gives a sense of the north direction. This is used in Plane Table Surveying

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Surveyor Compass) :

In surveyor's compass, the dimension quadrants are read in the dikuman system.

(A) Composition :- Surveyor's compass is an old directional instrument. It is also called Miner's Dial. It is a brass round box of 125 mm diameter, on the circumference of which two openings, Darsha and Vishya, exactly opposite to each other (in the opposite direction of diameter), are fixed by hinges. At the time of use, they are erected exactly vertical.

The viewing aperture has a vertical slit from which the target is viewed. A vertical swirl is attached to the slit of the visual borer, which is used for target piercing.

       Needle or pointer - Both ends of the needle of the surveyor's compass are pointed from the front. The needle can rotate freely on the rivet in the center and stop at the magnetic meridian direction.

Calibrated wheel or card – The calibrated wheel of the surveyor's compass is not attached to the needle, but is permanently attached to the box and rotates with it when the box is rotated. 

The marks on the calibrated wheel remain in the Quadrants system. The north (N) and south (S) directions have zero points (Zero) and the east (E) and west (W) directions have 90° points, but the east (E) and west (W) points on the wheel. The positions of the letters are interchanged. The marks remain in the surveyor's compass up to half a degree. 

(B) Experiment : - By setting the compass on a tripod at the station point, the target is seen from the turn of the spectator. The Line of Sight pierces the target by cutting through the wrinkle of the visual aperture. 

When these three are in a straight line, then turning around and looking at the tip of the needle at the northern end (under the glass-lid), the reading is read. As shown in the figure, the declination of the target is N 20° E.

Prismatic Compass) : A prism is necessarily attached to this compass, which shows the marks of the wheel (degrees) by magnifying it. Hence it is called Prismatic Dixchak.

Dikeman in compass is read in full circle Dikeman system. The specialty of the compass is that both target-peening and wheel reading are performed simultaneously and the surveyor does not have to change his position. Where fast work is required, prismatic pointers are preferred.

(A) Composition - In a prismatic compass, a triangular jam is attached to the lower part of the oblique bar, hence it is called a prismatic compass. This prism shows the degree marks on the calibrated wheel by straightening and enlarging it.

A prismatic compass is a brass round box 80 mm to 150 mm in diameter, in the middle of which a magnetic needle hangs over the rivet, which always shows magnetic meridian. The calibrated wheel in this compass is made of aluminum and is permanently attached to the magnetic needle pointer) and rotates with it.

     There are marks on the wheel from 0°-360°, these marks move in a clockwise direction. Zero or 360° marks are marked at the southern (S) end, 90° at the western (W) end, 180° at the north (N) end and 270° at the east (E) end. This is done because the readings are read through the prism at the southern end, which is exactly 180° to the target.

 (B) Experiment - Direction measurement can be done by holding a prismatic compass in the hand, but for best results, it should be fixed tightly on a light tripod

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