4_Angle and directions_2016_r1 - Chapter 4 Angle and...

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(Chapter 4) 1/20 Chapter 4 Angle and Directions One of the basic purposes of surveying is to determine the relative positions of points on or near the earth’s surface. Assigning coordinates to a given point is a useful and common way to indicate its position. Angles are usually measured to compute the coordinates of a particular point. Vertical angle A vertical angle between two lines of sight is measured in a plane that is vertical at the point of observation. Sometimes the two points sighted do not lie in the same plane. Angle of elevation angle measured upward from a horizontal reference line and is considered a positive (+) angle. Angle of depression angle measured downward from the horizon and is considered to be a negative (-) angle. Zenith direction an upward vertical direction usually used as a reference for measuring vertical angles. Zenith angle an angle measured with respect to zenith direction.
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(Chapter 4) 2/20 Horizontal angles An interior angle is measured on the inside of a closed polygon An exterior angle is measured outside of the closed polygon At any point, the sum of the interior and exterior angles must equal 360°. The sum of all interior angles in a closed polygon is equal to (180°)(n 2), where n is the number of sides. The sum of the exterior angles must equal (180°)(n + 2). An angle measured in a clockwise direction, from the rear to the forward point or station, is called an angle to the right. An angle turned counterclockwise from the rear to the forward station is called an angle to the left.
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