In civil engineering, it is most important to select the best survey methods according to the nature of land, time, money and accuracy needed. Chain surveying is used where the area to be surveyed is small and flat. However, when we need to survey in large areas, chain surveying alone is not sufficient and convenient. In such cases, it very important to use some sort of methods that enable angles or directions of the survey lines. For that, the best surveying methods is the compass surveying method.
Compass surveying is a branch of surveying in which directions of survey lines are determined with a compass and the lengths of the lines are measured with tape or a chain.
In practice, the compass is generally used to run a traverse. The word traverse means a series of straight lines means to pass across. In surveying, a traverse consists of a series of straight lines connected together to form an open or a closed polygon. Where the length of the traverse lines is measured with a chain or a tape.
The ends of the traverse lines are called traverse stations or traverse points.
At each traverse station, where the traverse lines meet, the angle is measured with a compass.
Instruments used in compass survey
- Prismatic compass
- Ranging rod
- Tripod stand (for the prismatic compass)
- Arrows and pegs
Compass survey is suggested when
- The area to be surveyed is large.
- time is limited.
- High accuracy is not required.
- High crowded area which creates difficulty in surveying.
- Site has a smoothly rising and falling form or outline.
Compass survey is not suggested when
- High accuracy is required
- The area is a magnetically disturbed example: area having magnetic rock, iron core or power line & sub-stations, etc.
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