Surveying is the very first step of any construction project and refers to the scientific technology that helps determine the position of all specific points and distances on a surface. Usually, these kinds of positions are 3D. In surveying, a few types of methods are used but one of the most common methods is compass surveying. In our below-mentioned sections, we will talk about compass surveying. Go through to learn every detail regarding compass surveying.
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See also: What is prismatic compass?
Compass surveying: What is it?
Compass surveying is an essential field of surveying and is normally used to define the position of objects by estimating both angles and lengths. Angles are measured with a compass and length with a chain or tape measure.
In some areas, compass surveying is highly preferred; those are:
- When surveying a large area like coastal or coarse areas of rivers
- When triangulation is impossible, if there are many obstacles to doing a chain survey because the area is crowded with a lot of detail.
- When a surveyor has a specific deadline to complete a survey of a large and detailed area
However, compass surveying also has some constraints. It is not recommended for areas hidden from public view, including magnetic material such as iron ore deposits, metal or steel structures, and power cables.
Compass surveying: Types of compass for surveying
Compass has a wide range of varieties. Those are as follows.
- Magnetic compass
- Prismatic compass or Lensatic compass
- Surveyor’s compass
- Liquid compass
- Marine compass or Card compass
- Baseplate compass or Orienteering compass
- Thumb compass
- Solid-state compasses
- Qibla compass
- GPS compass
- Gyro compass
- Astro compass
Among these above-mentioned types of compass, mainly three compasses are used for practical surveying:
- Prismatic compass
- Surveyor’s compass
- Level compass
Prismatic compass
Major parts of the prismatic compass are
- Magnetic needle
- Graduated ring
- Adjustable mirror
- Sliding arrangement for mirror
- Object vane
- Eye vane
- Metal box
- Glass cover
- Horsehair
The prismatic compass has two kinds of adjustments: permanent and temporary.
Surveyor’s compass
This compass has a round brass box with a magnetic needle that swings freely on a brass circle divided into 360 degrees.
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Compass surveying: Principle
Survey points are linked as a series of lines. The compass instrument’s magnetic bearings measure it. The angle between the lines is calculated, and the chain measures the length. It’s called a compass traverse. Compass traverse is calculated in two ways: open traverse and closed traverse.
Compass surveying: Common errors
In compass surveying, various kinds of errors can occur sometimes. Here are those errors.
- Instrumental errors
- Personal errors
- Natural errors
Instrumental errors
As the name implies, it is induced by inaccurate instrument settings. Other reasons are:
- Aiming and reading errors occur if the viewing surface is not vertical.
- Readings may not be accurate if the magnetic stylus is not perfectly straight or stiff.
Personal errors
If the surveyor is responsible for any kind of inaccuracy, then it is called personal error. These can be inappropriate levelling, wrong reading, or wrong detailing.
Natural errors
Natural errors are caused by various natural causes that affect compass operations. It has nothing to do with surveyors, and some modifications have been applied to the calculations to minimise them. These include proximity to the magnetic storm, local disruptions, and declination.
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Compass surveying: Advantages
- The equipment is easy to use and manage.
- No electrical energy is mandated.
- Appropriate for reconstructing paleo-surveys.
- Less workforce is needed.
Compass surveying: Disadvantages
- Reading accuracy is not very specific.
- Instrument errors occur repeatedly.
- Errors may take place due to range stick or poor vision.
FAQs
Which are the main compasses used for compass surveying?
The prismatic compass and surveyor compass are the two main compasses used for compass surveying.
Why is compass surveying preferred?
Compass is portable and quite light in weight. Also, the settings are easy to do. For these kinds of reasons, compass surveying is preferred.
What are the total 16v points of a compass?
Sixteen points present in a compass are N, NNE, NE, ENE, E, ESE, SE, SSE, S, SSW, SW, WSW, W, NWN, NW, and N NNW.
What is the cardinal point of a compass?
There are four principal points in a compass: North, South, East, and West. These four main points are known as the cardinal points of a compass.
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