(I) Closed Traverse:- A traverse is said to be closed when a complete circuit is made when it returns to the starting point forming a closed polygon.
Open traverse
(ii) Unclosed or open traverse:- A traverse is said to be open or enclosed when it does not form a closed polygon.
- The chief methods by which the direction of the survey lines may be determined are as follows. (A) By the chain angles ---In this method, the entire work is done with the chain and tape only. It is suitable for where the area cannot be divided into triangles. (B) By the free or loose needle method. In this method an angular instrument such as a compass or theodolite. For about compass
(C) Fast needle method --- In this method a theodolite is used to determine the bearing of each line.
(D) By the measurement of angles between successive lines. In this method, a theodolite is used for measurement of angles. The horizontal angles measured in a traverse may be (a) Included angles (b) Deflection angles between successive lines.
- Traverse survey with the use of theodolite
For the relative direction of the survey, lines are determined by two methods.
1. By the measurement of angles between successive lines.
2. By the direct observation of bearings of the lines.
1. By the measurement of angles between successive lines---This method is generally used in long traverse or where high precision is required. In this method bearing of the first line is measure and the angles of successive lines are measure with a theodolite or total station. The next steps of this method calculate the bearing of each line. It is calculated from bearing of initial line and the observed angles of successive lines.
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For theodolite traversing fieldwork consisting of i. Reconnaissance
ii. Selection, marking and referencing of station.
iii. Running of survey lines.
iv. Pick up the detail.
v. Booking of field notes.
Procedure:- Traversing by the method of included angles.
Set the instrument at A. Measure the bearing of the line AB, measure the angle HAB The theodolite set each successive stations BCDEFH and H, Measured angle ABC, BCD, CDE in a similar manner. The lines AB, BC, etc also measure with chain or tape. Detail of the survey also records in field book.
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2. By the direct observation of bearings of the lines.
Set up the instrument at Aand level it, Observe the fore bearing of the line AB.
Move the instrument at B and observe the back bearing of AB. Loosen the upper clamp and rotate the telescope in a horizontal plane until it is directed to C. Read the vernier A, which gives the bearing of BC.
Repeat the process at each of the subsequent stations.
Checks in closed Traverse
1. The sum of the measured interior angles should equal (2N-4) right angles.
2. The sum of the measured exterior angles should equal to (2N+4 ) right angles.
Where Nis the number of sides of the traverse.
Angular error of closure should not exceed:- Least count of the instrument ×√N
Check on Linear Measurement:- In the closed traverse the sum of the northing (distance measured north) should equal the sum of the southing ( distance measured south) . similarly , the sum of the easting (distance measured south) . sum of easting should be equal to the sum of the westing. if any discrepancy it indicate an error in chaining.
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