Converting Azimuths to Bearings or Vice Versa

Converting Deflection Angles to Bearings

Correcting for Local Magnetic Attraction

Engineering Aid 3 - Beginning Structural engineering guide book
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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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