Surveying Instruments - Practical Boundary Surveying - page 81

instrument person, so when the rod person is facing the instrument, as she usually
is, the instrument person must remember to tell her to move in a direction oppo-
site to the instrument person's left or right. Of course, if north, south, east or west
is used, both the instrument person and rod person must be aware of which way
north is. This shouldn't be a problem though—they are, after all, land surveyors.
A point-on-line is a point that is placed exactly on an established line. The line
could be a property line or a traverse line. A point-on-line is different than a trav-
erse point because the angle running through the point-on-line is always 180°.
Setting Up the Instrument or just Set Up means to set the instrument over a
point. As we have seen, this requires precisely leveling the instrument and tribrach
and precisely positioning the instrument and tribrach over a point.
All angles require three points: a Backsight , an Occupied Point and a
Foresight . The occupied point is the point on which the instrument is set up. The
backsight is the starting point from which the angle is measured. It is the point
where the instrument is zeroed. The foresight is the point being measured to or
being set.
Turning an Angle means the instrument person uses the total station to meas-
ure or set an angle on the instrument. When Measuring an Angle , three points are
fixed and the angle is measured between them. When Setting an Angle only two
points are fixed and the third point is to be set. Details of how this is accomplished
will be explained further on. Older instrument circles are numbered in both direc-
tions so angles can be read either left or right. When recording angles it is impor-
tant to note which direction the angle was turned. In data collectors, stored angles
are preceded by AR or AL for Angle Right or Angle Left. Total stations normally
measure all angles to the right from 0 to 360°.
When Taking a Shot , the instrument is used to measure the angle and dis-
tance to a point, usually to locate evidence. Locating evidence is also called a
Location , so the instrument person is sometimes said to be Making Locations
or Performing Locations . Taking a shot is also called a Sideshot . Often, multiple
sideshots are performed at a particular setup. Zero is set on a backsight and multi-
ple angles and distances are measured to various forms of evidence. For example,
we may need to locate a stone bound, a drill hole and the corners of a house. If
all of these points can be seen from one setup, sideshots will be used to measure
to each one. In such cases, it is only necessary to set zero on the backsight once.
In contrast, when traversing, it is only necessary to measure a single angle to the
foresight. The instrument will then be moved to the next point. In traversing it is
common to measure multiple angles between the backsight and foresight in order
to increase precision but there is still only one foresight, so the end result is a sin-
gle (averaged) angle. This measurement is called a Traverse Shot to differentiate
from a sideshot.
The distinction between a sideshot and a traverse shot is primarily important
when using a data collector. When taking sideshots, data collector software will
increment the point numbers of the foresight after each shot. However, it will not
increment the numbers of the occupied point and backsight, because they do not
change. When a traverse shot is taken, the instrument only turns a single (usually