Difference between Prismatic and Magnetic Compass
- 1. Survey Dr. Aman Kumar Singh, Dr. B. R. Ambedkar University Delhi October 13, 2024 Survey and Inspection Tools/ Equipment
- 2. Important Terms Leveling (i) To find the elevations of points with respect to a given or assumed datum, and (ii) To establish points at a given elevation or at different elevations with respect to a given or assumed datum. The first operation is required to enable the works to be designed while the second operation is required in the setting out of all kinds of engineering works. Leveling deals with measurement in a vertical plane. Surveying Survey is to horizontal distances. It is also measures Vertical distances between the points are, however, shown by contour lines, hachures or some other methods. Vertical distances are usually represented by means of vertical sections drawn separately.
- 3. Division of Survey (1) Plane Surveying (2)Geodetic Surveying. Plane Survey Plane surveying is that type of surveying in which the mean surface of the earth is considered as a plane and the spheroidal shape is neglected. The matter of fact that the length of an arc 12 kilometers long lying in the earth’s surface is only 1 cm greater than the subtended chord and further that the difference between the sum of the angles in a plane triangle and the sum of those in a spherical triangle is only one second for a triangle on earth’s surface cover 194 kilometers.
- 4. continue Geodetic surveyingis that type of surveying in which the shape of the earth is taken into account All lines lying in the surface are curved lines and the triangles are spherical triangles. It, therefore, involves spherical trigonometry. All geodetic surveys include work of larger magnitude and high degree of precision. The object of geodetic survey is to determine the precise position on the surface of the earth, of a system of widely distant points which from control stations to which surveys of less precision may be referred.
- 5. Type of Survey (1) Land Surveying (I) Topographical Survey (II) Cadastral Survey Calculation the land Area, fixing the properties line and transfer the properties. (III) City Survey Street , Water supply . sewerage systems etc. (2) Marine or Hydrographic Survey. (3) Astronomical Survey.
- 6. CLASSIFICATION BASED ON THE OBJECT OF SURVEY 1. Military 2. Engineering 3. Geological 4. Archaeological 5. Mine Instrument based (1) Chain survey (2) Theodolite survey (3) Traverse survey (4) Triangulation survey (5) Tacheometric survey (6) Plane table· survey (7)Photogrammetric survey and (8)Aerial survey.
- 7. UNITS OF MEASUREMENTS I. Horizontal distance 2. Vertical distance 3. Horizontal angle, and 4. Vertical angle. Figure: Basic Units
- 8. PLANS AND MAPS The representation is called a map if the scale is small while it is called a plan scale 1s large. on a plan, generally, only horizontal distances and directions are shown. On a topographic map, however, the vertical distances are also represented by contour lines. hachures or other systems. SCALES Scale is. the fixed ratio thai every distance on the plan bears with corresponding distance on the ground. One unit of length on the plan represents some number of same units of length on the ground, such as , etc. This ratio of map distance to the corresponding ground distance is independent of units of measurement and is called representative fraction. scale is 1 cm = 50 m Figure: RF Formula
- 9. Type of Scale Figure: Plain Scale
- 12. SURVEYING WORK The work of a surveyor may be divided into three 1. Field work 2. Office work 3. Care and adjustment of the instruments. DIRECT MEASUREMENTS The various methods of measuring the distances directly are as follows 1. Pacing· 2. Measurement with passometer 3. Measurement with pedometer 4. Measurement by odometer and speedometer 5. Chaining (a) Instruments for the direct measurement of directions : (i) Surveyor’s Compass (il) Prismatic Compass (b) Instruments for measurements of angles (I) Sextant · (ii) Theodolite
- 13. Figure: Units of angle measurement Bearing of a line is its direction relative to a given A meridian any direction· such as (I) True Meridian (2) Magnetic Meridian (3) Arbitrary Meridian.
- 14. True Meridian True meridian through a point is the line in which a plane, passing that point and the north and south poles, intersects with surface of the earth. It, thus,-passes through the true north and south. The direction of true meridian through a point can he established by astronomical observations. True Bearing line is the horizontal angle which it makes with the true meridian through one of the extremities of the line. Since the direction of- true meridian through a point remains fixed, the true bearing of a line is a constant quantity. Magnetic Meridian Magnetic meridian through a point is the direction shown by a freely floating and balanced magnetic needle free from all other attractive forces. 1ge direction of magnetic meridian can he established with the help of a magnetic compass. Magnetic Bearing The magnetic bearing of a line is line horizontal angle which it makes with the magnetic meridian. passing through One of the extremities of the line ’ A magnetic compass is used to measure it.
- 15. Arbitrary Meridian Arbitrary meridian is any convenient direction towards a permanent and prominent mark or signal, such as a church spire or top of a chimney. such meridians are used to determine the relative positions of lines in a small area. DESIGNATION OF BEARINGS The common systems of notation of bearings (a) The whole circle hearing system (W.C.B.) or Azimuthal system. (b) The Quadrantal hearing (Q.B.) system.
- 16. Figure: Conversion WCB into QCB
- 17. Figure: QCB/RB into WCB
- 18. FORE AND BACK BEARING Figure: Survey compass
- 19. Figure: Differenece between prismatic and Survey Compass
- 21. DEFINITIONS AND TERMS (1) The vertical axis. The vertical· axis is the axis about which the instrument can be rotated in a horizontal plane. This is the axis about which the lower and upper plates rotate. (2) The horizontal axis. The horizontal or trunnion axis is the axis about which the telescope and the vertical circle rotate in vertical plane. (3) The line of sight or line of collimation. It is the line passing through the intersection of the horizontal and vertical cross-hairs and the optical centre of the object glass and its continuation. 4. Face left observation. If the face of the vertical circle is to the left of the observer, the observation of the angle (horizontal or vertical) is known as face left observation.
- 22. 5. Face right observation. If the face of the vertical circle is to the right of the observer, )he observation is known as face right observation. 6. Telescope normal. A telescope is said to he normal or direct when the face of yhe vertical circle is to the left and the ”bubble (of the telescope) up”. 7. Telescope inverted. A telescope is said to inverted or reversed when of the vertical circle is to the right and the ”bubble down”. 8. Changing face. It is an operation of bringing The face of The telescope from left to right and vice versa. Thank you