Figure 15-18.—Tripod targets.well guyed and plumbed (fig. 15-18), and the legsshould be set in depressions to prevent lateralmovement. On uneven ground one leg may have to beshortened or dug in to maintain a symmetricalappearance from all directions. Signal cloth wrappedaround the tripod should be used only on low-order(fourth-order) work as it is almost impossible to makeit symmetrical around the station.BIPOD TARGET.— Bipod targets are moresimply constructed than tripods but are less stable andmust be strongly guyed. Figure 15-19 shows a standardsurveying biped target. It is carried disassembled in acanvas case about 53 inches long. It can be assembled,erected, and plumbed by two men in 15 minutes. If thistarget must be left standing in the weather for anyextended period, the rope guys should be replaced withwire and two more wire guys added to each end of thecrossbar. In soft ground the pointed legs will sinkunevenly because of wind action and rain; therefore,they should be set in holes bored in the end of woodenstakes driven flush or in a short piece of 2-inch by 4-inchlumber laid flat in a shallow hole.POLE TARGETS.— Pole targets(fig. 15-20)areseldom used because the station cannot be occupiedwhile the target is in place. In certain cases, as when anunoccupied station must be sighted and cutting of linesof sight is difficult or impossible, a pole target that canbe seen above the trees maybe erected The staff maybe constructed of 2-inch by 2-inch lumber or cut poles,varying from about 2 inches to 6 inches in diameter. Themethod of joining sections of 2-inch by 2-inch lumberand the construction of a panel target are shown in figure15-20. The targets must be plumbed by manipulation ofthe guy wires. Special care must be taken when warpedor crooked boards are used to construct pole targets, andthey must be checked for eccentricity.15-28
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