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surveying iii (topographic and geodetic surveys) - Modern Prepper

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(4) The program of observation is arranged in order to avoid all unnecessary changing of focus.At the first station, the observer should read the near rod before taking the first set of 25 observations.At the second station, the observer should make the near rod reading between the two sets ofobservations. The day's program for each observer is as follows: read the near rod <strong>and</strong> take a set ofobservations; move to the second station, take a set of observations, read the near rod, <strong>and</strong> take a set ofobservations; return to first station, take a set of observations, <strong>and</strong> read the near rod.(5) Observations should begin <strong>and</strong> end at the same time. A faster observer should continuereading until the slower observer has 25 readings. Both observers should stop at the same time.(6) The DE for each set of 25 observations per observer is computed, <strong>and</strong> the comparable setsfrom both observers are averaged. Sets 1 <strong>and</strong> 2, <strong>and</strong> sets 3 <strong>and</strong> 4 are then paired for a mean. The meanof pairs must agree within the AE for the length of section, as previously discussed under the criteria forfirst- <strong>and</strong> second-order leveling. The means of pairs are combined for a mean of sets (one day'sobservations), which must agree with the second day's mean of sets, within the AE. The two days'observations (mean of sets) are averaged to obtain the difference in elevation between the TBMs.PART C: TRIGONOMETRIC LEVELING4-10. General. Based upon the accurately determined elevation of an initial point, the elevations of allstations in a triangulation system can be determined by measuring the vertical angles between thestations. Apply the fundamentals of trigonometry, <strong>and</strong> use these vertical angles to compute thedifferences in elevations. This process is known as trigonometric leveling.a. Trigonometric leveling is usually a part of triangulation or traverse work, with the transit ortheodolite used to determine the vertical angle <strong>and</strong> the measured distance. The determinations bytrigonometric leveling are checked at reasonable intervals by a connection with lines run by instrumentalleveling. In order to provide starting <strong>and</strong> check elevations, a complete scheme of vertical-angleobservations should be carried through all triangulation.b. This complete scheme consists of a continuous series of vertical angles measured through themain scheme of triangulation, observations made on each line over which horizontal angles are observed(the observations over each line to be made in both directions if both ends of the line are occupied), <strong>and</strong>observations of vertical angles upon all supplementary <strong>and</strong> intersection stations corresponding to thehorizontal angles measured upon such stations.c. As you recall, a vertical angle, as measured with a transit, is the angle measured vertically up ordown from a horizontal plane of reference. When the telescope is pointed in the horizontal plane (level),the value of the vertical angle4-25 EN0593

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