Presentation.pptx soil and water conservation engineering

Compass survey

1. Surveying Surveying may be defined as the method of making measurements of the relative positions of natural & man-made features on the earth's surface and the presentation of this information either graphically or numerically. Surveying is the art of determining the relative positions of objects on the surface of the earth by taking measurements in the horizontal and vertical planes

2. Compass surveying Compass surveying is a type of surveying in which the directions of surveying lines are determined with a magnetic compass, and the length of the surveying lines are measured with a tape or chain or laser range finder. The compass is generally used to run a traverse line.

3. Principle of compass surveying Compass surveying relies on a technique called  Traversing , which uses a network of interconnected lines.  The distances between the lines are measured using a chain or tape, and the magnetic bearings of the lines are measured using a surveyor compass.

4. Instruments: Prismatic compass Tape Ranging rods Tripod Arrows Plumb Bob

5. Types of compass:   Prismatic compass Level Compass Surveyor Compass. 

6. Prismatic compass Parts of a prismatic compass are as follows:  Cylinder shaped metal box Pivot Magnetic needle Prism Graduation circle Object vane Eye vane Eye silt Eye hole Sunglasses Spring break Reflector mirror Focussing stud Lifting pin Lifting lever

7. Prismatic compass adjustments: Temporary adjustments include the following:  Centering Leveling Focussing the prism Permanent adjustment of a prismatic compass includes the following:  Adjustment of levels Adjustment of sight vanes Adjustment for sensitivity of needles Adjustment for straightness of needles Adjustment of pivot

8. Bearing of prismatic compass WHOLE CIRCLE BEARING

9. Surveyor compass A surveyor compass is an instrument used for the measurement of horizontal angles and the bearing of a line of sight. The Surveyor compass is commonly referred to as the  Circumferentor .

10. Parts The parts of the surveyor compass are listed below:  Box Lifting lever Pivot Glass top Circular graduated arc Sight vane Jewel bearing Lifting pin Magnetic needle  Rider Metal pin  Object vane 

11. Bearing of survey compass QUADRANTAL BEARING

12. Sifference between surveyor and prismatic compass Prismatic Compass Surveyor Compass Graduation circle is fixed to a broad type needle. Hence, it will not rotate with the line of sight. Graduation circle is fixed to the box. Hence, it rotates with the line of sight. There is a prism at the viewing end. At the viewing end, there is no prism. There is only a slit. Sighting and reading can be done simultaneously Sighting and viewing cannot be done simultaneously. The magnetic needle does not act as an index. Magnetic needle acts as index while reading

13. The graduations are in whole circle bearing. The graduations are in the quadrantal system or called Reduced Bearing.  Graduations are marked inverted since their reflection is read through prism. Graduations are marked directly. They are not inverted. The reading is taken through a prism. The reading is taken by directly viewing from the top glass. Tripods may or may not be used. It can be held on a stretched hand also. Tripod is essential for using it.

14. Bearing in compass survey QUADRANTAL BEARING WHOLE CIRCLE BEARING REDUCED BEARING FORE AND BACK BEARING

15. Whole circle bearing The magnetic bearing of a line measured clockwise from the North Pole towards the line, is known as the 'whole circle bearing', of that line. Such a bearing may have any value between 0º and 360°. The whole circle bearing of a line is obtained by prismatic compass.

16. Quadrantal bearing The magnetic bearing of a line measured clockwise or counterclockwise from the North Pole or South Pole (whichever is nearer the line) towards the East or West, is known as the ' quadrantal bearing'

17. Reduced bearing When the whole circle bearing of a line is converted to quadrantal bearing, it is termed the 'reduced bearing’. Thus, the reduced bearing is similar to the quadrantal bearing. Its value lies between 0° and 90°, but the quadrants should be mentioned for proper designation.

18. Fore and back bearing The bearing of a line measured in the direction of the progress of survey is called the 'fore bearing' (FB) of the line. The bearing of a line measured in the direction opposite to the survey is called the 'back bearing' (BB) of the line.