What is Compass Surveying? Compass Surveying Advantages and Disadvantages
What is Compass Surveying? Compass Surveying Advantages and Disadvantages
What is Compass Surveying?
Compass surveying is a surveying technique that makes use of a compass to determine the direction of survey lines. This is a relatively simple technique that is often used in the early stages of surveying before more sophisticated techniques are employed.
A prismatic compass is a navigation and surveying tool that is widely used to determine the bearing of the traveling and the angles between them, waypoints (course endpoints), and direction.
Compass surveying is a kind of surveying in which surveying lines’ directions are established using a magnetic compass and their lengths are measured using a tape, chain, or laser range finder.
A compass is often used to draw a traverse line. The compass computes line bearings with regard to the magnetic needle. The included angles can then be determined using appropriate formulae in the case of clockwise and anti-clockwise traverses.
Surveyors take two bearings for each survey line in the traverse, fore bearing and back bearing, which should differ by 180° if the local attraction is insignificant.
It is called a Prismatic compass because it is primarily made up of a prism that is used to make more precise observations.
Compass surveying is the use of the simplest surveying instrument, a compass, to establish land or boundary lines.
Unlike Total Station Surveying which is more precise, Compass Surveying is quick and most often used for construction estimates.
Compass Types used for Surveying
The compass types are:
Prismatic Compass
A prismatic compass is a portable magnetic compass that may be used as a handheld device or mounted on a tripod. It has a prism that is used to accurately measure readings.
The best feature of this compass is that it can be used for both sighting and reading without moving position.
The Adjustments of the prismatic compass are:
Temporary Adjustment
This adjustment is used to adjust the compass while the instrument is being carried. The adjustment consists of moving a pin and the needle or card moves with it. Adjustment can be made in either direction.
Temporary Adjustment comprises of:
- Centering-Centering is the process of precisely positioning the compass over the station where the bearing is to be determined. A small pebble or plumb bob is dropped to check the centering.
- Leveling-If the instrument is used in hand or mounted on a tripod, it must be leveled. When held in hand, the graduated disc should swing freely and appear to be completely level in relation to the top edge of the case.
When a tripod is used, it usually has a ball and socket arrangement for leveling.
- Focusing-Prism moves up and down in its slide till the graduations of the aluminum ring are clear and sharp
Permanent Adjustment
This is used to fix the card or needle in a definite position. In this method, a notch is cut in the compass housing at the desired position of the card. The edge of the card is placed on this notch and chiseled out to hold it in place.
They are only performed when the prism’s internal components have been disturbed or damaged. They are as follows:
- Adjustment of the pivot point
- Adjustment of sight vanes
- Adjustment of needle
- Adjustments in levels
Surveyors Compass
A surveyor’s compass is made out of a circular brass box carrying a magnetic needle that swings freely over a 360-degree brass circle.
The horizontal angle is measured with a pair of sights situated on the compass’s north-south axis. They are typically supported by a tripod and leveled with a ball and socket mechanism.
Level Compass
The level compass is a simple, needle-style compass with a spirit level at its center, fixed to require no adjustment for accuracy.
It is used for surveying horizontal angles such as angles in a building and related measurements and is accurate only when the card’s plane of rotation remains perpendicular to the horizontal plane.
Compass Surveying Instruments
The equipment used to carry out Compass Surveying are:
1. Prismatic Compass
A prismatic compass is a portable magnetic compass that may be used as a handheld device or mounted on a tripod. It has a prism that is used to accurately measure readings. The best feature of this compass is that it can be used for both sighting and reading without moving position.
2. Tape
measure. This is a type of measuring tool that consists of two tapes, one that flows with the wind, and another that remains fixed. With a tape-measure it is easy to measure any kind of distance because the tape-measure can go straight through any contour.
3. Tripod
A tripod is a device made of two poles that are linked together in the center by three legs, each leg has a round section on its bottom. The round section rests on the ground and the legs are adjusted so that their top is at the same level. A sighting compass is mounted on top of a tripod.
4. Chaining Rods
A Chaining Rod is a device that can be used to measure the distance between two points. A set of two consecutive parallel rods is clipped together with a spring clip. The rod that has not been released from the clip is then used to measure the distance between the first and second points.
5. Plumb Bob
A plumb bob is a tied weight that hangs from a string or wire. The weight has a line attached to it that is marked with measurements. The plumb bob can be used to find the height of an object because the plumb bob points at the center of gravity of a straight object.
6. Arrows
An arrow is a straight stick that has been sharpened at the end and is used to point at something. Arrows can be made from any kind of material, but are usually made from metal or plastic.
7. Ranging Rods
A ranging rod is a measuring tool that can measure the exact distance between two points. It is essentially a rod with a known length and an attached scale.
Ranging rods have different scales to allow for measurements that are in multiples of 2, 3 or 5 meters. Ranging rods come in sets of 4, 6 or 8 meters and are used in gaging work when it’s important to be able to measure precise distances.
Compass Surveying Uses
The major uses of Compass Surveying areas are outlined below.
- It is useful for checking plans and subdivision maps.
- It is helpful to establish a point of reference to make the total station or GPS systems more accurate.
- it is used for temporary surveying as well as permanent work such as land surveys, boundary surveys, topographical maps, aerial surveys, and layout projects.
- Compass surveying is used to determine the length of each side of a triangle, any curve, and any circle.
- It is also used in the construction industry to measure slopes and as a checking tool when constructing lines and relative positions of objects.
- In road and railway construction, it is used to check elevations and the straightness of alignments.
- It is also used in mining, oil prospecting, and land grading.
- Compass Surveying is also used in gas exploration, oil drilling, and other fields that require measurements in remote locations.
- In geological exploration, compass surveying is used to determine the length and direction of a line.
- Compasses are used in archaeology to survey relics such as temples, graves or rock carvings.
Compass Survey Principle
The principle of compass surveying is traversing, which consists of a series of connected lines. The magnetic bearing of the lines is measured using a prismatic compass, and the distance (lengths) are measured using chain.
It shields the compass and serves as the entire casing or body of the compass.
Compass Survey Errors
Instrumental Error
They occur as a result of incorrect instrument adjustments, as the name implies. Other reasons include:
When the plane of sight is not vertical, errors in sighting and reading occur.
Readings may be inaccurate if the magnetic needle is not perfectly straight or sluggish.
Personal Error
They are primarily the result of the surveyor’s carelessness.
They are as follows:
- Inadequate leveling
- Incorrect centering
- Incorrect reading
Natural Error
Natural errors arise as a result of different natural causes that impact the operation of the compass. It has nothing to do with the surveyor, and in order to reduce them, some calculations were corrected. They are as follows:
- Attractions in the area
- The proximity to magnetic storms
- Declination
Compass Surveying Advantages
They include:
- The magnetic compass is used by all types of people, both young and old.
- It is a great way to learn about the art of original surveying which are located everywhere in the world.
- Compass survey techniques require very little physical exertion, making it comfortable for everyone involved.
- It can be used to measure any distance when there is no overhead power supply or the lighting conditions are not suitable for using a laser rangefinder
- The compass reading can be corrected by comparing it with the base map which was pre-established.
- Compass surveying is not affected by magnetic fields and can therefore be utilized in any location of the world.
- It is a great way to spend your time since you don’t have to pay for education or equipment, nor do you need training or practice because it’s used in many industries.
- There is no need for any formal education or training since it is self-explanatory to anyone who is interested.
- There are no requirements for a license, permit or experience.
Compass Surveying Disadvantages
The main disadvantages of Compass Surveying are outlined below.
- The compass is an old method of surveying, which involves a lot of manual calculations, making the process complicated and the data not very precise.
- The compass is not very accurate, nor can it be easily relocated after it has been set or moved.
- Calculations can be time-consuming, depending on the distance between the points to be surveyed.
- Some places require a permit to conduct compass surveying
- It takes longer to survey a large area since calculations have to be done manually and cannot be done electronically.
- The compass does not give an exact coordinate of an object, making it unreliable for certain projects and applications.
- Compass surveying can be difficult to measure distances during night time, requiring the use of a light source
- Compass is not considered reliable for very long distances- a few hundred meters or kilometers.
- Compass can make wrong turns, while a laser rangefinder works perfectly in all directions.
- Compass is not very accurate in measuring horizontal distances.
- Non-compass surveying technology is easier, cheaper and faster
- In compass surveying, it may be difficult to make adjustments and corrections to the base map since there are no exact measurements or coordinates.
- It may not be clear for a person who grew up with a GPS system or devices that require an internet connection where to start when surveying areas that do not have any sort of network coverage.
The objective of compass surveying
Compass surveying is a significant part of surveying that is commonly used to determine the location of an item using both angular and linear measurements.
A compass is used to obtain angle measurements, while chain or tape is used to calculate linear measures.
Limit of accuracy in compass surveying
The inaccuracy in angular measurement in compass surveying should not be more than 5 minutes. As a result, the maximum accuracy is 5 minutes.
Linear measurement in compass surveying should not be more than 10% of the length of a traverse.
If the error is more, then it would not be good practice and should be avoided.
Compass Surveying FAQs
What is compass surveying?
Compass Surveying is a type of surveying in which the directions of points and lines are determined by means of a magnetic compass. It is used to establish horizontal and vertical control in surveys, and to fix the position of a point in relation to others.
Compass surveying is an old-time surveying technique that is still used today. It is a simple process that uses a compass to measure the angles between two points.
This information is then used to create a map or drawing of the area. Compass surveying is a quick and easy way to map an area, and it is a great tool for hikers and campers.
What are the uses of compass surveying?
Compass surveying is a significant part of surveying that is commonly used to determine the location of an item using both angular and linear measurements.
A compass is used to obtain angle measurements, while a chain or tape is used to calculate linear measures.
What are the applications of compass surveying?
Compass surveying is a significant part of surveying that is commonly used to determine the location of an item using both angular and linear measurements.
A compass is used to obtain angle measurements, while a chain or tape is used to calculate linear measures.
What are the types of compass surveys?
The Surveyor’s compass and the Prismatic compass are the two major types of magnetic compass used in surveying, and both are featured in the collection.
The surveyor’s compass is the bigger and more precise instrument, and it is frequently mounted on a stand or tripod.
Where is compass surveying suitable?
The surveyor’s compass is suitable for any location that does not have an overhead power supply, or where the lighting conditions are not suitable for using a laser rangefinder.
Do you need a license for compass surveying?
You do not require any license to conduct compass surveying, but there are certain restrictions that should be followed.
Compass surveys may only take place between 6am and 6pm. You should also follow the established rules regarding trespassing and vandalism.
Is compass surveying dangerous?
Compass surveying is not an offensive or dangerous activity. It can be done by adults of all ages, including children over the age of 14. It is not a quick process and can take several hours to survey an entire area.
What kind of subjects does compass surveying include?
This method can be used to measure any distance when there is no power supply or lighting conditions are not suitable for using a laser rangefinder.
Does compass surveying require previous experience?
No. It can be used by anyone who is interested and has a basic understanding of the subject since the calculations are very simple.
What are the advantages of compass surveying?
Compass surveying is a significant part of surveying that is commonly used to determine the location of an item using both angular and linear measurements.
The surveyor’s compass is more precise than other types of compasses, and it is often mounted on a stand or tripod.
What is the difference between prismatic and surveyor compass?
Prismatic compass is somewhat smaller, does not require a tripod, and can be used under all lighting conditions.
What is the distance measurement of a compass?
A surveyor’s compass can measure any distance, as long as there are no power supply or lighting conditions are not suitable for using a laser rangefinder.
What are the precautions in compass surveying?
To prevent local interest, the surveyor should not carry anything made of iron or steel, such as a bundle of keys, iron buttons, and so on.
As much as feasible, the instrument should not be placed near telegraph poles, trains, other steel structures, current-carrying wires, and so on.
Which method is more accurate in plotting a compass survey?
If a line’s length and bearing are known, its projection on the y- and x-axes may be computed and displayed.
This approach is the most accurate of all charting methods since it eliminates the necessity of a protractor and allows each point to be plotted independently of the others.
In which areas does compass surveying is not recommended?
Compass surveying is not suggested in places where magnetic substances such as steel constructions, iron ore deposits, and electric lines transmitting currents are suspected.
What are the 2 types of compasses?
Magnetic compass and gyrocompass are the two primary forms of the compass.
What is a compass?
A compass is an instrument used for finding direction by the line of magnetic force (magnetism).
What is the main purpose of a compass?
Compasses were invented for land measurements and navigation. They are also useful to survey personnel, install fans and ventilation ducts in mines, measure distances and determine latitude when used with a GPS receiver.
Which bearing is measured in the direction of survey?
Fore bearing: The term “fore bearing” refers to the angle measured in the direction of the survey’s progress. Back bearing is the angle measured in the opposite direction of the survey’s progress.
What is the least count of the compass?
The Surveyor Compass’s Least Count is 15′, or fifteen minutes. This implies that the sensor can only display readings in 15-minute increments.
What is the feature of the surveyor compass?
The Surveyor’s Compass has a larger sighting device with a higher range and better accuracy. It is normally mounted on a tripod, allowing it to be used under any lighting conditions.
What is the main disadvantage of a prismatic compass?
A prismatic compass cannot be used when there are overhead power supplies or magnetic fields, as they will interfere with its readings. Additionally, they are much more expensive than most other types of compasses.
What are the advantages and disadvantages of a prismatic compass?
The advantages of a prismatic compass are: it is more powerful than other compasses, it can be used in any lighting conditions, and they cost much less than other types of compasses.
The disadvantages include: they cannot be used near overhead power supplies or magnetic fields, are less accurate than surveyor’s compasses and are difficult for the inexperienced user to read.
What is the difference between a compass and a sextant?
A sextant is powered by either mechanical or electronic means. A sextant has two sighting mirrors and markings that indicate bearing. A compass has only one sighting device and no markings.
