Jumaat, 13 Mac 2009

Compass Rose, Azimuth, and Quadrants

•Compass Rose A compass rose is the familiar north, east, south, west cross-symbol used to show direction on a map. There are two methods of selecting a bearing, and they depend on which style of compass rose is used. The azimuth method is based on a 360° circle. A bearing is reported as an angle between the bearing line and 0°, measured clockwise around the compass rose.

Measuring Azimuth

The quadrant method is based on a division of the compass rose into four quadrants. Bearings are read as the angle between north or south and the bearing line in either the east or west direction. For example, in the image, a bearing line midway through the NW quadrant of the compass rose can be read as 315° (start at north, turn 315° - [azimuth method]) or as N 45° W (start at north, turn 45° to the west - [quadrant method].)

•Normally, the quadrant method of reporting bearings is easiest to use. One advantage is in converting from a bearing to its mirrored bearing in the opposite direction. For example, if a bearing from point A to point B is given as N 55° W, the reverse bearing from B back to A is S 55° E; one has only to reverse the compass directions while keeping the same angle. Azimuths are useful when you need to process them using a computer because each bearing can be represented by a single number.

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