What is a traverse survey?

Traverse surveying is a popular method of surveying. Traversing is that type of survey where several connected survey lines form a framework and the directions and lengths of the survey lines are measured with the help of a tool to measure angles and tape or chain respectively. Traverse networks involve placing survey stations in a queue or trail and using pre-tested points as a basis for looking at the next point. This type of surveying is different from Tacheometric surveying, where only angles are measured and the process of chaining is reduced.

Types of traverse surveying

Traverse surveying can be of two types.

• Open traverse
• Closed traverse

Open traverse

It is said to be an open traverse when traverse begins somewhere and ends at another point, as shown in the illustration from station A to station E. Open traverse is also called unclosed traverse The open traverse is the least desirable type of traverse because it does not give a check for field service or start-up data. The open traverse is especially useful for controlling the initial and construction surveys on highways, roads, pipelines, transmission lines, and the like.

Closed traverse

The traverse is said to closed traverse when it forms a closed circuit as shown in the figure. In this case, both the starting point and the endpoint across are parallel. The closed traverse can also end at a point whose relative position is known. Suitable for exploration of lake boundaries, stadiums, forests, etc. The closed traverse or loop traverse starts and ends at the station's hypothetical links and external azimuth affecting statistics, location, or relative station position. If, however, links should be tied to the existing grid system, disconnection starts from a known channel and azimuth in that program. While the loop traverse provides some exploration fieldwork and math, of course, provide an initial data check or confirm the detection of all system and linear errors that are possible in research.

Methods of traversing

Traversing or traverse surveying is done in four different ways and these methods are categorized according to the test tool used. The methods are as follows.

• Chain traversing
• Compass traversing
• Theodolite traversing
• Plane table traversing

Chain traversing

Chain traversing is done by taking only linear measurements. Moreover, a chain is enough for chain traversing. The angle between adjacent lines is measured using the concepts of chain angles. Breaking the chains is done in places like lakes etc. where it is difficult to use trilateration. The concept of chain angle is nothing but finding an angle between two adjacent sides by establishing a third party using binding channels. The method is not suitable for accurate work and is often used when angle measurement tools such as a compass, sextant, or theodolite are available.

Compass traversing

In the case of a cross-sectional compass, both linear and angular cross-sectional measurements are taken using a chain and a prismatic compass respectively. Both the fore bearing and back bearings are measured and the necessary adjustments are applied to the surface attractiveness. If any closing error is detected during traverse editing, the Bowditch rule is used to correct the total error.

At the crossing of the chain and compass, the magnetic bearings of the test lines are measured with a compass and the length of the lines is measured with a chain or tape. The direction of the magnetic meridian is established at each crossing point independently. The path is also known as the tree or the way of the loose needle.

Theodolite traversing

In this type of traversing, the traverse legs are measured by tying the straight chains of the traverse angles to all the traverse stations and accurately measuring with the theodolite.

The first test should be done with a diagram drawn on the area using almost the same area of ​​the intersection channel and taking important details, the channel disagreement should be examined. Theodolite traversing requires the marking tools of the channel as anchors, arrows, etc.

Measure with theodolite

The multiplication method is used to measure traverse angles with a much better degree of accuracy than that can be achieved with a small amount of vernier embedded in the theodolite. In this method, the angle measures three or four times by holding the vernier clamp when it sees the rear station. While moving from the transmission station to the rear station, the top plate is released and made free to rotate. So mechanical reading adds up many times as many repetitions. The difference between the first and last five readings is the combined horizontal angle and the median angle and is obtained by dividing the combined angle by the multiplication value.

Plane table traversing

In plane table traversing, measurement and paper cutting arrangements are performed simultaneously. The plane table equipment is set to all transit stations individually in a clockwise or opposite direction. The sides of each traverse station are drawn on paper with appropriate scales.

Advantages of traversing

• Minimal testing and order required.
• While in some systems, which may require a survey to be performed near a solid polygon structure, the traverse can change to any shape and thus be able to carry many different locations.
• Only a few observations are required for each station, and in some research networks it should be considered and considered a large angular and linear observation.
• Traverse networks do not have the power of mathematical thinking that takes place in triangular systems.
• The scale error is not as inclusive as cutting. Azimuth swing errors can also be reduced by increasing the distance between channels.

Plotting a traverse surveying

There are two main methods of traverse surveying:

Angle and distance method

This method is of three types

• By a protector
• By the tangent of an angle
• By an angle chord

Coordinate method

In the figure, the latitude $\left(L\right)$ or y-coordinate and the departure $\left(D\right)$ or x-coordinate of the line AB of length $l$ and reduced bearing $\left(rb\right)$ are given by

$L=+l \cos \left(rb\right)$ and $D=+l \sin \left(rb\right)$

To calculate latitude and departure of traverse lines, it is first necessary to reduce the load on the quadrant system. Signs of latitude and departure will depend on reduced line load.

Additionally, linking the latitude and departure of any point with reference to the preceding point is equal to the latitude and departure of the line connecting the preceding point to the projected point. Such links are also known as consecutive co-ordinates or dependent coordinates.

Context and Applications

In Civil engineering under surveying, traversing is a field method used to check different control networks. This includes placing points on the line of access to standard conditions. Survey points or stations for basic observations. The purpose of the traversing is to find unknown points that are related to each other and to find all the points within the cross-section that are related to the normal grid. Three initial data elements are required. They are links to the first position and azimuth in the visible azimuth marker.

This topic is important for professional exams in both undergraduate and graduate courses like-

• Bachelors of Technology in Civil Engineering
• Masters of Technology in Civil Engineering

Practice Problems

Q 1. Which of the following is the method of traverse surveying in survey?

a. Measurement of all lengths

b. Measurement of all angles

c. Measurement of angles and distances

d. Measurement of all bearings

Correct option- c

Explanation- The traverse is enhanced by measuring the distance and angles between the points located on the site boundary.

Q 2. What is Bowditch rule also called?

a. Axis rule

b. Transit rule

c. Graphic rule

d. Compass rule

Correct option- d

Explanation- Bowditch rule is also termed as Compass rule.

Q 3. What will happen when the whole circle bearing of a traverse line of any length is between 0⁰ to 90⁰ of coordinate?

a. The latitude is positive and departure is negative.

b. The departure is positive and latitude is negative.

c. Both latitude and departure are positive.

d. Both latitude and departure are negative.

Correct option- c

Explanation- In the first quadrant both the latitude and departure are positive.

Q 4. What is the degree of the curve for a radius (R) of 573 meters (m) using chain of 20 meters length?

a. 1

b. 2

c. 3

d. 4

Correct option- b

Explanation- for 20 meter chain length,

The degree of the curve (D) is given by:

D=1146/R

Given,

R=573 m

So,

D=1146/573

D=2⁰

Q 5. What is the most appropriate method to balance crossing when angular measurements are more accurate than line measurements?

a. Transit rule

b. Bowditch rule

c. Axis rule

d. Arbitrary method

Correct option- a

Explanation- Legally, the absolute error at latitudes and departure is still equal to the latitude and departure of the sides.