(1) To test the theodolite for proper vertical collimation, level the instrument carefully, bring the
image of the vertical circle into view by turning the changeover knob (13), sight the horizontal crosshair
onto a clearly defined object, and record the reading. Reverse the telescope, resight the object, and
record the second reading. Halve the second reading and add 90 minutes. This should result in exactly
the same reading obtained in the first position. If it does not, a collimation error or index error of the
vertical circle exists.
(2) To adjust the vertical circle to the proper reading, place the telescope in the first position.
Set the micrometer scale to the proper seconds reading obtained in the vertical collimation check. Direct
the telescope on the object. Use the vertical slow-motion screw (14) and bring into coincidence the
graduation lines which give the proper reading. Turn the collimation level adjusting screw (21) to bring
the level bubble to center. Repeat the measurement of the vertical angle, as with the collimation check,
and add the two readings. The sum of the readings should now be within 10 seconds of 180 minutes. If
it is not, repeat the entire correction procedure.
PART C: TRAVERSING AND TRAVERSE TYPES
3-14. General. Traversing is a form of control survey that is used in a wide variety of surveys.
Traverses are a series of established stations linked together by the angle and distance between adjacent
points. The angles are measured by theodolites, and the distances are measured by EDME. The AISI
total station combines both of these functions. Detailed information pertaining to traverse design, data
collection, and limitations are discussed in the SSGCN.
a. Starting Control. The purpose of a traverse is to locate points relative to each other on a
common grid. Surveyors need certain elements of starting data such as the coordinates of a starting
point and an azimuth to an azimuth mark. Surveyors should make an effort to use the best data available
to begin a traverse. Survey control data is available in the form of existing stations (with the station data
published in a trigonometric list) or new stations that were established by local agencies who can
provide the station data.
b. Open Traverse. An open traverse (Figure 3-13, page 3-28) originates at a starting station,
proceeds to its destination, and ends at a station whose relative position is not previously known. The
open traverse is the least-desirable traverse type, because it does not provide the opportunity for
checking the accuracy of the fieldwork. All measurements must be carefully collected, and every
method for checking position and direction must be use. The planning of a traverse should always
provide for closure of the traverse.