This Article Covers “What Is Compass Traversing” Types Of Traversing And Methods Of Traversing One By One.
A type of survey that involves both linear as well as angular measurements known as Compass Traversing.
In Traverse surveying the directions of survey lines re fixed by angular measurements and not by forming a network of triangles as done in chain surveying.
A traverse survey is one in which framework consist of a series of connected lines, the length and directions of which measured with a chain or tape and angular instruments respectively.
The routine of changing and offsetting is the same as in chain surveying.
The running of check lines is not necessary.
Types Of Traverse
There are generally two types,
- A traverse said to closed when a complete circuit made i.e when it returns to the starting point forming a closed polygon OR when it begins and ends at points whose positions on plan known.
- The work may checked or “balanced”.
- Suitable for locating bounders of lakes, woods etc and for the survey of moderately large area.
- A traverse said to open or unclosed when it does not form a closed polygon.
- It consist of connecting lines extending in the same general direction and not returning to the starting point.
- Similarly it does not start and end as points whose positions on plan known.
- It is suitable for the survey of long narrow strip eg river, coast line, road, railway etc.
Method of Traversing
The different methods by which the direction of the survey lines may be determined are as follows:
- By the Chain angles.
- Free or loose needle method.
- By the fast needle method.
- By the measurement of angles between successive lines.
Method of Chain Angles or Chain Traversing
- In this method entire work done with the chain or tape only.
- When survey of an area such as lake, wood, standing crops etc required, so area cannot be divide into triangles.
- A traverse therefore to run round the area and in the absence of an angler instrument, the angles between the successive lines fixed by measuring the lines with a chain.
- Angles fixed by measurement known as Chain Angles.
- The angles at the station fixed by internal tie lines such a1,a2, or external such as b1,b2, c1,c2, d1,d2.
- The angle at A fixed by measuring the distance a1 and a2 suitably chosen on AD and AB, b3 to check accuracy.
In open traverse Angeles at B and C fixed by ab and cd and so on.
By the Free or Loose needle method
- In this method an angular instrument such as Compass or Theodolite set up at each of the successive stations and the bearing of each line taken with reference to the magnetic meridian and not with reference to the adjacent lines.
- Hence the errors are not cumulative but compensating.
- The result obtain are not generally so accurate as those obtained by methods 3 and 4
By the fast needle method
- In this method a theodolite used for determine the bearings of each line.
By the measurement of angles between successive lines
- In this method a theodolite used for measurement of angles.
- The horizontal angles measured in a traverse may 1) included angle 2) deflection angles between successive lines.
- The method of included angles is the most accurate method and generally used for large surveys and accurate work.
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