surveying iii (topographic and geodetic surveys) - Modern Prepper

is 0. When the telescope is pointed up at a higher feature (elevated), the vertical angle increases from 0and is called a plus vertical angle. These values increase from 0° to +90° when the telescope is pointedstraight up. As the telescope is depressed (pointed down), the angle also increases in numerical value.A depressed telescope reading showing that it is below the horizontal plane is called a minus verticalangle. These numerical values increase from 0° to -90° when the telescope is pointed straight down.d. To determine the difference in elevation between two points, set up and level the instrument atone point. Hold the rod at another point. Point the telescope at an easily read value (a full meter) on therod, and measure the vertical angle (Figure 4-12). Determine the horizontal distance (ED) between theinstrument and rod by taping, obtaining a stadia reading, or by triangulation. You may also determinethe slope distance (EB) using EDME. Whichever distance (ED or EB) is selected, one side and oneangle () of a right triangle should be determined. Using this information, compute the other sides andangle. For trigonometric leveling, only the side opposite the measured angle, the difference in elevation,is computed.Figure 4-12. Trigonometric Leveling With the Telescope in an Elevated Position(1) The computation consists of multiplying the measured distance by the proper trigonometricfunction of the measured angle (sine, if the slope distance [EB] is measured; tangent, if the horizontaldistance [ED] is measured). Where AE is the height of the instrument above point A, and BC is theheight of the line of sight above point C, the difference in elevation between A and C is AE + BD - BC.(2) This method of determining the difference in elevation should be limited to horizontaldistances less than 300 meters when moderate precision is sufficient and to proportionately shorterdistances when higher precision is required.EN0593 4-26