| @bsd987: an azimuth (also called bearing) is a direction measured clockwise from north. For example, due east is 90º, due south is 180º, southwest is 225º, etc. If from a point you have two lines, one running in southwest direction (azimuth = 225º) and the other in southeast direction (azimuth = 135º), you subtract 225 - 135 = 90 degrees, so the angle between both lines is a right angle. |