By: Scott Hunt and Jonathan Funtanilla
Traversing
WHAT IS A TRAVERSE?
A traverse a series of consecutive connected lines of known lengths related to one another by
known angles. The lengths of the lines are determined by direct measurement of horizontal
distances and by slope measurement. These line courses run between a series of points called
traverse stations. The angles at the traverse stations are measured by tape, transit, theodolite,
compass or total stations. These angles can be interior angles, deflection angles, or angles to the
right and the lengths and azimuths or bearings of each line of the traverse are estimated through
field measurements
TYPES OF TRAVERSING
OPEN TRAVERSING
When it comes to traversing there are two distinct types to look at. The First method is referred
to as open traversing. Open traversing starts with a known pre-determined point already
determined with respect to a horizontal datum, and end at an unknown horizontal position further
down the line. Thus open traverses end without closing the loop and are geometrically and
mathematically open. Hubs (steel or wooden stakes) are used in open traversing and set at each
traverse station where a change in direction will occur. Spikes, Nails and scratched crosses are
used when the change of direction occurs on pavement, while or painted marks are made on
concrete.
Open traverses should be avoided if at all possible because they offer no means of checking for
observational errors and mistakes. If they must be used, observations should be repeated as well
as distance and angles measurements, forward and backward, and then the averaged to carefully
guard against surveying errors. Open traverses are typically used for plotting a strip of land
which will be used to plan a route in road construction.
CLOSED TRAVERSING
The second and more common traversing method is known as closed traversing. There are two
distinct categories for closed traversing which include the polygon and link method. In the
polygon traverse, the lines return to the starting point, thus forming a closed figure that is both
geometrically and mathematically closed as shown below. The second method of closed
traversing is referred to as link traversing. Link Traversing finish upon another horizontal station,
which is defined by its geographic latitude and longitude, Y- and X coordinates on a grid system,
or by its location in relation to a fixed boundary. Link Traversing should have a positional
accuracy that is equal to or greater than that of the starting original starting point.
USES OF TRAVERSING
Traverses are used to find accurate positions of a small number of marked stations. From these
stations, less precise measurements can be made to features to be located without accumulating
accidental errors. Thus, traverses usually serve as control surveys. When construction plans are
created, stations can be used as beginning points from which to lay out work. When construction
takes place, a system of traverse stations in the area must be established and surveyed. These
traverse surveys are used for a variety of different purposes which include:

Determining the positions of exiting boundary markers.

Establishing the positions of boundary lines.

Finding the area encompassed within a boundary.

Determining positions of arbitrary points from which data can be obtained for. (Example
establishing control points for map creation).

To establish ground control for photographic mapping.

To establish control points for gathering data and locating railroad, highway, utility work.
METHODS OF TRAVERSING
There are a verity of methods used in observing angles and directions of traverse lines which
include: interior angles, angles to the right, deflection angles, and
Azimuths.
Traversing by Interior Angles (Most Common)
Interior angle traversing is used in a variety of different types of work, but are especially
convenient for property surveying. Interior angles can be observed in either a
Clock-Wise or Counter-Clockwise direction but in order to reduce mistakes in reading,
recording, and computing, they should always be turned clockwise from the backsight station to
the foresight station. Precision of interior angles can be improved by averaging equal numbers
of direct and reversed readings.
Traversing by Angles to the Right
Angles observed clockwise from a backsight on the rear traverse station towards the foresight on
the forward traverse station are referred to as angles to the right. This is normally done by
numbering consecutive traverse stations so that they increase in the forward direction.
Depending on the direction of the traversing, angles to the right may be interior or exterior
angles within a polygon traverse. If the direction of traversing is counter clockwise, then
clockwise interior angles will be observed. If the direction of traversing is clockwise, then
exterior angles will be observed. By averaging equal numbers of direct and reversed readings,
observed angles to the right can also be checked and their accuracy improved.
Traversing by Deflection Angles
Route surveys are commonly run using deflection angles observed to the right or left from the
lines extended. Deflection angles cannot exceed 180° and can be obtained by subtracting 180°
from angles to the right. Positive values should be denoted as right and negative to left.
Traversing by Azimuths
With help of a total station, traverses can be calculated using azimuths. This process permits
reading azimuths of all lines directly, which eliminates the need to calculate them. Since
Azimuths are observed clockwise from the north end of the meridian. The instrument is oriented
at each setup by sighting on the previous station with either the back azimuth on the circle or the
azimuth (if deflection angles are turned), followed by the forward station. Thus the resulting
reading on the horizontal circle will be the forward line’s azimuth.
TRAVERSE LENGTHS
The length of each traverse line must be calculated while preforming a traverse. The easiest and
most economical method of accomplishing this involves the use of a total station. Total stations
are used due to their high levels of accuracy and speed at completing the task. One such distinct
advantage of traversing with total station instrument is that both angles and distances can be
calculated at each station setup. Traverse lengths on a construction sites depend on the allowable
limits of closure as well as on the use and extent of the traverse. In closed traverses, each course
is observed and recorded as a separate distance, and on long link traverses such as highways and
railroads, distances are carried along continuously from the starting point using stationing.
SELECTING TRAVERSE STATIONS AND REFERENCING
Selecting positions for setting traverse stations can vary with the type of survey being conducted.
A few guidelines to consider when choosing stations include:

accuracy

utility

efficiency (number of setups)

Number of instrument setups.
However, utility may override using very long lines because intermediate hubs, or stations at
strategic locations, may be needed to complete the survey’s objectives.
Once these stations are positioned they must be referenced for future checks. This is
accomplished by referencing benchmarks in the area or by citing features in the area such as
trees and buildings.
ANGLE MISCLOSURE FOR TRAVERSING
The angular misclosure for interior-angle traverse is the difference between the sum of the
observed angles and the geometrically correct total for the polygon. The sum, of the interior
angles of a closed polygon should equal: ∑ = (n - 2) x 1800 n= number of sides
If the direction of the traverse is clockwise when observing angles to the right, exterior angles
will be observed. In this case, the sum of the exterior angles will equal: ∑ = (n + 2) x 1800 n =
number of sides
Permissible misclosure can be computed by the formula
C= k√N , n = number of angles, K= constant related to accuracy.
AREA OF A CLOSED TRAVERSE
When a closed traverse has been completed the area within can then be calculated. This is done
using the methods of calculation.
1) ABC =1/2 acsin(alfa) when you have three sides a,b,c (referred to as the triangle method)
When the area of the traverse has greater then three sides eg: 6 sides ,you can split the area in
half into two triangles and take the sum.
ERRORS IN TRAVERSING
SYSTEMATIC ERRORS:
A systematic error is an error that always has the same magnitude and sign under the same
conditions. These errors are caused by physical and natural conditions that vary depending on the
circumstance. Some examples include:

Incorrect prism setting on total station.

Curvature and refraction

Incorrect length of a level rod.
RANDOM ERRORS:
A random error is an error that does not follow any fixed relation to the circumstances of the
observation. These types of errors are produced by irregular causes beyond the control of the
observer.
HUMAN ERRORS:
Human errors are caused by errors the observer makes during surveying process.
INSTRUMENT ERRORS:
Instrument errors are caused by imperfections in the design and construction of the surveying
equipment. Some of these errors include:


Calibration of the total station.
Laser leveling error.
CALCULATION ERRORS:
Calculation errors occur during the adjustment process of surveying. These errors include:

Misclosure calculation errors (angular and linear)
References
 http://www.engr.mun.ca/~sitotaw/Site/Fall2007_files/TP_Manual_CloseTra
vers-ENGI3703.pdf
 http://engineeringtraining.tpub.com/14069/css/14069_463.htm
 http://www.firefightermath.org/index.php?option=com_content&view=artic
le&id=58&Itemid=72
 http://www.globalsecurity.org/military/library/policy/army/fm/3-34331/ch6.htm
 http://classof1.com/homework_answers/civil_engineering/traverse_surveyin
g/
 www.globalsecurity.org
 http://www.floridageomatics.com/publications/gfl/chapter-three.htm
 http://www.oc.nps.edu/oc2902w/geodesy/geolay/gfl84b_a.htm