Converting Azimuths to Bearings or Vice Versa

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You  know  from  the  bearing  of  BC  that,  angle S´BC  measures  50°.  The  interior  angle  ABC  is The sum of the interior and exterior angles at any  traverse  station  or  point  equals  the  sum  of all   the   angles   around   that   point,   or   360°. Therefore, the exterior angle at station B equals 360°  minus  the  interior  angle  or The process of measuring angles around a point to  obtain  a  check  on  their  sum,  which  should equal   360°00’,   is   sometimes   referred   to   as CLOSING   THE   HORIZON. Converting Azimuths to Bearings or Vice Versa Suppose  you  want  to  convert  an  azimuth  of 135° to the corresponding bearing. This azimuth is greater than 90° but less than 180°; therefore, the line lies in the southeast quadrant. As shown in  figure  13-3,  the  bearing  angles  are  always measured   from   the   north   and   south   ends   of thereference  meridian.  (When  solving  any  bearing Figure 13-3.-Converting azimuths to corresponding bear- ings or vice versa. problem, draw a sketch to get a clear picture.) For the azimuth, the horizontal direction is reckoned clockwise  from  the  meridian  plane.  It  is  measured between either the north or the south end of the reference  meridian  and  the  line  in  question.  When we  talk  about  azimuth  in  this  training  manual, however, you must understand that the azimuth is  referenced  clockwise  from  the  NORTH  point of the meridian. The numerical value of this 135° azimuth  angle  is  measured  from  the  north. Therefore, in this figure, the value of the bearing is The  complete  description  of  the  bearing  then  is S45°E. For example, if you want to convert a bearing of N30°W into an azimuth angle, you know that the   angle   location   must   be   in   the   northwest quadrant.  Then,  draw  an  angle  of  30°  from  the north end of the reference meridian because you measure  azimuth  angles  clockwise  from  the  north end  of  the  reference  meridian.  To  compute  this azimuth angle, subtract 30° from 360°; the result is 330°. Therefore, the bearing of N30°W is equal to  330°  azimuth  angle. ESTABLISHING  DIRECTION  BY SURVEYOR’S   COMPASS The basic method of establishing direction of a  survey  line  or  a  point  is  with  a  surveyor’s compass.   (Notice   that   on   most   surveyor’s compasses,  the  east  and  west  indicators  are  in  the opposite  positions  from  those  of  the  east  and  west indicators on a map or chart.) In figure 13-4, an Figure 13-4.-A magnetic compass reading corrected for local attraction. 13-3

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