Elementary. Angles and directions

Transcription

1 Elementary Surveying Angles and directions

2 Prepared by: Andre Paul C. Ampong 3

3 Vertical angles Vertical angles are referenced to: The horizon by plus or minus The zenith The nadir Zenith and nadir are terms describing points on a celestial lsphere a sphere of infinitely i large radius with its center at the center of the earth. Prepared by: Andre Paul C. Ampong 4

4 Celestial sphere Prepared by: Andre Paul C. Ampong 5

5 Meridians Prepared by: Andre Paul C. Ampong 6

6 Meridians A line on the mean surface of the earth joining the north and the south poles is called a meridian. All longitudes are meridians. The term meridian can be more precisely defined by noting that it is the line formed by the intersection i of the earth s surface of the plane that includes the earth s axis of rotation. The meridian, as described, is known as the geographic meridian, astronomic meridian, or the true meridian. Prepared by: Andre Paul C. Ampong 7

7 Earth s two norths Magnetic meridians are meridians that are parallel to the directions taken by freely moving magnetized needles, as in a compass. Whereas true meridians are fixed, magnetic meridians vary with time and location. Prepared by: Andre Paul C. Ampong 8

8 Grid meridians Grid meridians are lines that are parallel l to a grid reference meridian (central meridian). True meridians converge to meet at the pole; grid meridians are all parallel to the central meridian. In the case of a small scale survey of only limited importance, meridians are sometimes assumed, and the survey is referenced to that assumed direction. Prepared by: Andre Paul C. Ampong 9

9 All horizontal directions are referenced to meridians. Prepared by: Andre Paul C. Ampong 10

10 Horizontal angles Close traverse. Open traverse. Deflection angles are measured from the prolongation of the backline to the forward line. The angles measured either to the left (L) or to the right (R) of the projected line. The direction (L or R) must be shown along with the numerical value. Prepared by: Andre Paul C. Ampong 11

11 Azimuths An azimuth is the direction of a line as given by an angle measured clockwise from the north end of a meridian. In some circumstances, azimuths are measured clockwise from the south end of the meridian; when that is the case, the directions are clearly labeled as to the angle orientation. Prepared by: Andre Paul C. Ampong 12

12 Bearings A bearing is the direction of a line as given by the acute angle between the line and a meridian. The bearing angle, which can be measured clockwise or counterclockwise from the north or south end of the meridian, is always accompanied by the letters that locate the quadrant in which the line falls (NE, NW, SE or SW). The four cardinal directions are usually designated by the terms due north, due south, due east and due west. However, due west, for example, can also be designated as N 90 o W (or S 90 o W). Prepared by: Andre Paul C. Ampong 13

13 Relationship between bearings and azimuths Prepared by: Andre Paul C. Ampong 14

14 Magnetic north Located hundreds of miles south of the geographic North Pole lies the magnetic North Pole at approximately North and West (2005), northwest of Canada's Sverdrup Island. However, this location is not fixed and is moving continually, even on a daily basis. Prepared by: Andre Paul C. Ampong 15

15 Prepared by: Andre Paul C. Ampong 16

16 Magnetic declination Prepared by: Andre Paul C. Ampong 17

17 Magnetic declination Prepared by: Andre Paul C. Ampong 18

18 Magnetic declination Prepared by: Andre Paul C. Ampong 19

19 Slides may be downloaded from: mindthreshold.wordpress.com Prepared by: Andre Paul C. Ampong 20