Figure 15-18.—Tripod targets.
well guyed and plumbed (fig. 15-18), and the legs
should be set in depressions to prevent lateral
movement. On uneven ground one leg may have to be
shortened or dug in to maintain a symmetrical
appearance from all directions. Signal cloth wrapped
around the tripod should be used only on low-order
(fourth-order) work as it is almost impossible to make
it symmetrical around the station.
BIPOD TARGET.— Bipod targets are more
simply constructed than tripods but are less stable and
must be strongly guyed. Figure 15-19 shows a standard
surveying biped target. It is carried disassembled in a
canvas case about 53 inches long. It can be assembled,
erected, and plumbed by two men in 15 minutes. If this
target must be left standing in the weather for any
extended period, the rope guys should be replaced with
wire and two more wire guys added to each end of the
crossbar. In soft ground the pointed legs will sink
unevenly because of wind action and rain; therefore,
they should be set in holes bored in the end of wooden
stakes driven flush or in a short piece of 2-inch by 4-inch
lumber laid flat in a shallow hole.
POLE TARGETS.— Pole targets (fig. 15-20) are
seldom used because the station cannot be occupied
while the target is in place. In certain cases, as when an
unoccupied station must be sighted and cutting of lines
of sight is difficult or impossible, a pole target that can
be seen above the trees maybe erected The staff may
be constructed of 2-inch by 2-inch lumber or cut poles,
varying from about 2 inches to 6 inches in diameter. The
method of joining sections of 2-inch by 2-inch lumber
and the construction of a panel target are shown in figure
15-20. The targets must be plumbed by manipulation of
the guy wires. Special care must be taken when warped
or crooked boards are used to construct pole targets, and
they must be checked for eccentricity.
15-28
