TRAVERS SURVEY

Definition of Travers Survey

Traversing is the type of survey in which a number of connected survey lines form the framework and the directions and lengths of the survey lines are measured with the help of an angle measuring instrument and tape or chain respectively.
Traverses are structures that form a series of straight lines that know the value of a number of directions and lengths.

Types of Traversing or Travers Survey

There are two types of traverse surveying. They are:
(A) Closed traverses
(B) Open traverses

(A) Closed traverses:– A circle that starts from a certain point and turns around at different points and ends at the starting point and creates a limited area is called a closed circle.
(B) Open Traverse:- An enclosure that starts from a specific station and ends at another station point, that is, does not end at the starting point, is called an open enclosure.

Suitability

The closed traverse is suitable for locating the boundaries of lakes, woods, etc. and for a survey of large areas. the open traverse is suitable for surveying a long narrow strip of land as required for a road of the canal or the coastline

Sub-perimeter

In the second phase of the traverse survey, for the convenience of work, a relatively small perimeter with an average area of 20 square miles is given in the main perimeter. This small perimeter is called a sub-perimeter. Actual Northline with the help of astrological observations.
The area is determined by determining the actual bearing of the arms of the traverses, calculating the latitude and longitude of the arms by calculating them systematically in the traversal array of the main scale, and designing the perimeter structure according to the individual coordinates through necessary corrections.

Mouza or Village Fence

The last task of the traversing team is to make a skeleton map or P-60 seat with mouza or pram fence. The village is called Gher. The station point has to be finished by burying hard bamboo poles by marking the border near the outer boundary. The structure of the enclosed enclosure according to the type of situation of the boundary of the mouza The length of the arms of the traverses and which ones are measured and written in the field book with the help of chains or high-quality tape. Knox scale: 18 ” = 1 mile, 32 ” = 1 and mile, 64 ” = 1 mile- the design of the mouza thus prepared The structure design is called. The design is handed over to the employee/officer engaged in the detailed survey work. The main purpose of the traverse survey is to prepare the structure design of each village or mouza survey area. The location of a sufficient number of vowel points is traversed at traversing. If the original structure design is not correct then the detailed design cannot be accurate at all.

Methods of Traversing or Travers Survey

There are several methods of traversing, depending on the instruments used in determining the relative directions of the traverse lines. The following are the principal methods:
1. Chain traversing
2. Chain and compass traversing

Chain Traversing:
The method in which the whole work is done with chain and tape is called chain traversing. No angle measurement is used and the directions of the lines are fixed entirely by linear measurements Angles fixed by linear or tie measurements are known as chain angles. The method is unsuitable for accurate work and is generally used if an angle measuring instruments such as a compass, sextant, or theodolite is available.

Chain and Compass Traversing:-
In chain and compass traversing, the magnetic bearings of the survey lines are measured by a compass and the lengths of the lines are measured either with a chain or with a tape. The direction of the magnetic meridian is established at each traverse station independently. The method is also known as a tree or loose needle method.

Travers Survey by Fast Needle Method

The method in which the magnetic bearings of traverse lines are measured by a theodolite fitted with s compass is called traversing by fast needle method. The direction of the magnetic meridian is not established at each station but instead, the magnetic bearings of the lines are measured with a reference so that direction of the magnetic meridian established at the first station. There are three methods of observing the bearings of lines by fast needle method.
1. Direct method with transiting,
2. Direct method without transiting,
3. Back bearing method.

Travers Survey By Direct Observation Of Angles

In this method, the angles between the lines are directly measured by a theodolite and the magnetic bearing of other lines can be calculated in this method. The angles measured at different stations may be either
1. Included Angles and
2. Deflection Angles

Traversing By Direct Observation Of Angles

An included angle at a station is either of the two angles formed nby two survey lines meeting there and these angles should be measured clockwise. The method consists simply of measuring each angle directly from a back sight on the preceding station. The angled may also be measured by repetition. The angles measured from the back station may be interior or exterior depending on the direction of progress.

In Fig(a) the direction of progress is counter-clockwise and so the angles measured clockwise are the interior angle. In Fig(a) the direction of progress is clockwise and so the angles measured clockwise are the exterior angle.

Traversing by Deflection Angles

A deflection angle is an angle in which a survey line makes with the prolongation of the preceding line. It is designated as right (R) or left (L) as it is measured clockwise or anti-clockwise from the prolongation of the previous line. This type of traversing is more suitable for the survey of roads, railways, pipelines, etc where the survey lines make small deflection angles.

Errors in Traversing or Travers Survey

The errors involved in closed traversing are two kinds:
1. Linear Error and
2. Angular Error
The most satisfactory method of checking the linear measurements consists of chaining each survey line a second time, preferably in the reverse direction on different dates and by different parties. The following are checks for the angular work:

A. Travers by included angles:

The sum of measured interior angles should be equal to (2N-4), where N=number of sides of the traverse.
If the exterior angles are measured, their sum should be equal to (2N=4)p/2

B. Travers by deflection angles:

The algebraic sum of the deflection angles should be equal to 360 degree taking the right hand and deflection angles as a positive and left-hand angle as negative.

C. Traversing by direct observation of bearings:

The force bearing of the last line should be equal to its back bearing 180 degree measured from the initial station.

Checks in Open Traverse

No direct checks of angular measurements are available. So indirect checks can be made. As illustrated in Fig(a) the addition to the observation of bearing of AB at station A, bearing of AD can also be measured., if possible. Similarly, at D, the bearing of DA can be measured, and check applied. If the two bearings differ by 180 degree, the work may be accepted as correct

Another method, which furnishes a check when work is plotted is shown as in Fig (b) and consists of reading the bearing to any prominent point P from each of the consecutive stations. The check-in plotting consists in laying off the lines AP, BP, CP, etc, and noting whether the lines pass through one point.