Figure 13-23.-Range ties.
Figure 13-24.-Locating a point by
distances from two
distance. The method requires extra instrument
manipulation and should be used only when none
of the previous methods are satisfactory for use.
Actually, range ties establish not only the corner
of a structure but also the alignment of one of
the sides. In figure 13-23, assume that the building
is not visible from either A or B or that either or
both of the distances from A to B to a corner of
the building cannot be measured easily. With the
instrument set up at either A or B and the line
AB established, one member of the party moves
along AB until he reaches point R, which is the
intersection of line 1-2 extended. The instrument
is moved and set up on R, and the distance along
the line AB to R is measured. An angle measure-
ment to the building is made by using either A
or B as the backsight. The range distance, R-2,
is measured as well as the building dimensions.
SETTING ADJACENT POINTS
To set a point adjacent to a traverse line
means to establish the location of a point by
following given tie data. This tie data may be
(1) a perpendicular offset distance from a single
specified station, (2) angles from two stations, or
(3) an angle from one station and the distance
from another station.
Setting Points When Given
a Perpendicular Offset Distance
To set a point when given an angle and its
distance from a single station, you simply setup
the instrument at the station, turn the designated
angle, and chain the distance along the line of
sight. For perpendicular offset, the angle is 90°.
To set a point when given a distance from each
of two stations, you can manage by using two
tapes if each of the distances is less than a
full tape length. To do so, you set the zero end
of the tapes on both stations, run out the tapes,
and match the distance mark on each tape to
correspond with the required distance from the
stations. When the tape is drawn taut, the point
of contact between the tapes will be over the
location of the desired point.
If one or both of the distances is greater than
a full tape length, you can determine direction of
one of the tie lines by correct triangle solution.
For example, in figure 13-24, you want to set
Point B 120.0 ft from station A and 83.5 ft from
station C. A and C are 117.0 ft apart. You can
determine the size of the angle at A by triangle
solution as follows:
To set point B, you can set up a transit at A,
sight on C, turn 41°14´ to the left, and measure
off 120.0 ft on that line of sight. As a check, you
can measure BC to be sure it measures 83.5 ft.
Setting Points When Given
Angles from Two Stations
To set a point when given the angle from each
of two traverse stations, you should ordinarily