Linear Measurement and Compass Surveying
Recall different Methods for the Linear Measurements
Linear measurements refer to the measurement of distances or lengths in surveying. There are several methods used to measure distances, including:
- Chain surveying: A traditional method that uses a chain or tape to measure distances. The chain or tape is stretched between two points, and its length is used to determine the distance between them.
- Tacheometry: A method that uses a theodolite to measure distances. The theodolite is set up at one end of the distance to be measured, and a stadia rod or a reflector is placed at the other end. The theodolite is then aimed at the rod or reflector, and the distance can be calculated based on the angle and the height of the instrument.
- Electronic distance measurement (EDM): A modern method that uses electronic instruments to measure distances. EDM instruments use light or radio waves to measure distances, and are faster and more accurate than traditional methods.
- Photogrammetry: A method that uses aerial or satellite photographs to measure distances. The photos are analyzed to determine the scale and orientation of the features, and the distances between them can then be calculated.
Each method has its advantages and disadvantages, and the choice of method will depend on the specific requirements of the survey and the conditions of the terrain.
Chain surveying is a traditional method of surveying that uses a chain or tape to measure distances. The chain or tape is made of a flexible material such as steel or fibreglass, and is calibrated to a known length. The chain or tape is stretched between two points, and the length of the chain or tape is used to determine the distance between the two points.
Chain surveying is typically used for relatively short distances, and is well suited to flat, open terrain. It is relatively simple and inexpensive, but is also relatively slow and can be affected by environmental factors such as wind or temperature changes.
In chain surveying, the chain is supported by poles at regular intervals to ensure that the length of the chain is accurately maintained. The ends of the chain are held by two people, and one person walks along the chain while the other person records the distance. The accuracy of the survey depends on the accuracy of the chain and the skill of the surveyors.
Chain surveying is typically used for preliminary surveys, and is often followed by more accurate methods such as tachymetry or EDM.
The following are the types of chains used in surveying:
- Steel tape: Steel tapes are the most commonly used chains in surveying. They are durable, flexible, and accurate, and are available in a range of lengths and thicknesses. Steel tapes are often used in chain surveying, and can also be used in other types of surveying such as tachymetry or EDM.
- Fibreglass tape: Fibreglass tapes are similar to steel tapes, but are made of a lighter and more flexible material. They are often used in areas where a steel tape would be too heavy to carry, such as in mountainous terrain.
- Gunter’s chain: Gunter’s chain is a type of chain that is specifically designed for surveying. It consists of 100 links, each of which is 7.92 inches long. Gunter’s chain is used primarily for land surveys, and is still used in some parts of the world today.
- Engineer’s chain: Engineer’s chain is similar to Gunter’s chain, but is longer, with each link being 100 feet long. Engineer’s chains are used for large-scale surveys, such as for highways or pipelines.
The type of chain used in a survey depends on the nature of the survey, the accuracy required, and the terrain. Steel tapes and fiberglass tapes are the most commonly used chains in surveying, but Gunter’s and Engineer’s chains are still used in some applications.
Measuring tapes are essential tools used in surveying to measure linear distances between two points. There are several types of measuring tapes that are commonly used in surveying, including:
- Steel Tapes: Steel tapes are the most common type of measuring tapes used in surveying. They are made of thin steel strips and are flexible, making them easy to handle. Steel tapes are widely used for both indoor and outdoor surveying.
- Fibreglass Tapes: Fiberglass tapes are also commonly used in surveying. They are more durable than steel tapes and are resistant to wear and tear. They are also more resistant to weather conditions, making them ideal for outdoor surveying.
- Open Reel Tapes: Open reel tapes are similar to steel tapes but are mounted on a reel. They are useful for measuring longer distances.
- Closed Reel Tapes: Closed reel tapes are similar to open reel tapes but are enclosed in a case. They are more durable and are used for rough terrains and tough weather conditions.
Overall, the type of measuring tape used in surveying depends on the surveyor’s needs, the nature of the survey, and the conditions of the environment.
In chain surveying, several accessories are used to ensure accuracy and precision in linear measurements. Some of the commonly used accessories in chain surveying are:
- Arrows: Arrows are used to indicate the ends of a chain line, ensuring that the line is extended in the right direction.
- Pegs: Pegs are used to mark the positions of the stations, helping to ensure the line is set up in the correct position.
- Tripods: Tripods are used to support the level or dumpy level instrument, providing stability and accuracy in leveling.
- Ranging Rods: Ranging rods are used to provide a reference for the instrument, allowing for accurate alignment and measurements.
- Plummets: Plummets are used to determine the verticality of the leveling instrument, ensuring that the instrument is set up in a vertical position.
- Ranging Poles: Ranging poles are used to determine the distance between two points, helping to ensure accuracy in measurements.
- Measuring tapes: Measuring tapes are used to measure horizontal distances, complementing the chain measurement and providing additional precision.
The functions of the various accessories used in chain surveying are as follows:
- Arrows and Pegs: Arrows and pegs are used to mark the points on the ground that have been measured or surveyed. They help in maintaining accuracy and ensuring that the correct points are being measured.
- Ranging Rods: Ranging rods are used to align the survey line and to check the accuracy of the measurements. They are usually made of wood or metal and are usually painted in alternating colours (red and white) to make them easily visible.
- Offset Rod: Offset rods are used to measure distances that are not directly along the survey line. For example, they can be used to measure the distance from a wall or obstacle to the survey line. They are usually telescopic and can be adjusted to different lengths.
In surveying, various minor instruments are used to carry out various tasks efficiently and accurately. Some of the most commonly used minor instruments include:
- Compass: It is a directional instrument used for finding the direction of lines and locating the magnetic meridian.
- Prismatic Compass: It is used for measuring horizontal and vertical angles.
- Abney Level: It is used for measuring vertical angles and slopes.
- Dumpy Level: It is used for levelling and determining elevations.
- Clinometer: It is used for measuring vertical angles and slopes.
- Optical Square: It is used for finding the right angle in a survey.
- Cross Staff: It is used for measuring angles and heights in surveying.
- Pegs and Arrows: They are used for marking reference points in the field.
These minor instruments play an important role in carrying out surveying tasks with precision and accuracy.
Ranging refers to the process of aligning survey measurements to a known reference line or point. It is used to establish the location of the survey line relative to other points in the field. In chain surveying, ranging is the process of setting up a straight line between two points using ranging rods or other similar instruments, so that measurements can be made accurately along this line. The ranging process helps ensure that the measurements taken in the field are accurate and consistent.
- Direct Ranging: Direct ranging is a method in which survey lines are established by directly sighting on to the required points along the line. This method is simple, quick, and does not require any calculations.
- Indirect Ranging: Indirect ranging is a method in which survey lines are established by measuring and setting out intermediate points along the line. This method is more accurate than direct ranging, but it requires calculations and is more time-consuming. Indirect ranging is often used in areas where there are obstructions or when greater accuracy is required.
Both of these methods are commonly used in chain surveying and are chosen based on the requirements of the survey and the conditions of the field.
The procedure to measure the length with the help of tape or chain involves the following steps:
- Setting up the starting point of the measurement: The starting point is marked using an arrow or peg.
- Stretching the tape/chain: The tape or chain is stretched from the starting point to the end point of the measurement.
- Holding the tape/chain: The tape or chain is held by two people, one at the starting point and the other at the end point, to ensure its level and straightness.
- Reading the scale: The measurement is taken by reading the scale on the tape or chain at the end point.
- Recording the measurement: The measurement is recorded in a field book or any other recording medium.
- Repeating the procedure: The procedure is repeated if multiple measurements are needed to be taken.
It is important to ensure that the tape or chain is held straight and level during the measurement, as this can affect the accuracy of the measurement. Additionally, proper care and maintenance of the tape or chain should be taken to prevent any damage to the instrument.
Errors due to incorrect chain measurement in surveying can occur due to various reasons. Some of the common causes are:
- Tension: If the chain is not stretched tight enough, it will lead to measurement errors. The chain should be pulled taut to ensure accuracy.
- Temperature: Some chains may stretch or contract due to temperature changes, leading to incorrect measurements.
- Wear and Tear: Over time, chains can become worn or damaged, which can also cause errors.
- Incorrect Chain Length: If the chain is not the correct length, it will lead to incorrect measurements.
- Inconsistent Chain Length: If the chain is not uniform in length, it will lead to errors in the measurements.
- Human Error: Improper handling or incorrect measurements can also lead to errors in chain surveying.
To prevent these errors, it is important to regularly maintain and calibrate the chain and to properly use the chain and handle it correctly during the measurement process.
It refers to how a surveyor can accurately measure the length of a line on a terrain that is not flat.
There are two main methods to measure length on uneven/sloping ground:
- The Gradient Method: This method involves measuring the gradient or slope of the ground using a clinometer or an inclinometer. The length of the line is then calculated by multiplying the horizontal distance by the slope.
- The Optical Method: This method involves the use of optical instruments such as a theodolite or a level to take measurements from one point to another along the line. The vertical difference between the two points is recorded and used to calculate the length of the line.
By using these methods, a surveyor can accurately measure the length of a line on uneven or sloping ground and make accurate maps and surveys.
Errors in chaining can occur due to several reasons, including human errors, instrument errors, or environmental factors. Some of the common errors in chaining are:
- Pulling of Chain: This error occurs when the chain is pulled in a different direction from the line of sight, causing the measured length to be greater than the actual length.
- Sagging of Chain: This error occurs when the chain hangs vertically downward from the end points, causing the measured length to be less than the actual length.
- Stretch of Chain: This error occurs when the chain is stretched due to its own weight or due to external forces, causing the measured length to be greater than the actual length.
- Curvature of Chain: This error occurs when the chain is not kept straight, causing the measured length to be less than the actual length.
To correct these errors, various corrections can be applied, such as:
- Correction for Pulling of Chain: This correction involves measuring the pull on the chain and then subtracting it from the measured length to get the actual length.
- Correction for Sagging of Chain: This correction involves measuring the sag in the chain and then adding it to the measured length to get the actual length.
- Correction for Stretch of Chain: This correction involves measuring the stretch in the chain and then subtracting it from the measured length to get the actual length.
- Correction for Curvature of Chain: This correction involves measuring the curvature in the chain and then subtracting it from the measured length to get the actual length.
It is important to note that these corrections are applied to the measured length to get the most accurate and precise length measurement possible.
Errors in chaining can be classified into two main categories: systematic errors and random errors.
Systematic errors: Systematic errors are errors that occur consistently in the same direction or magnitude and affect the accuracy of the measurements. These errors can be caused by factors such as incorrect chain length, incorrect temperature compensation, and incorrect chain tension.
Random errors: Random errors are errors that are inconsistent in direction and magnitude and affect the precision of the measurements. These errors can be caused by factors such as human error, chain stretch, and measurement errors due to obstacles.
To minimise errors in chaining, it is important to use a well-maintained chain, properly tension the chain, and follow correct procedure in making the measurements. Additionally, multiple measurements should be taken to reduce the effect of random errors.
In surveying, errors in measurement can occur due to various factors, such as the curvature of the earth, the elasticity of the chain, or human error. To compensate for these errors, various correction methods are used to improve the accuracy of the survey results. The following are the common corrections that are classified in surveying:
- Correction for Curvature and Refraction: The earth is not flat but curved, and therefore, the correction for curvature and refraction is applied to account for the effects of the earth’s surface on the survey measurement. Combined correction for curvature and refraction is given by 0.06728 d2.
- Correction for Tension: This correction is applied to compensate for the elasticity of the chain. The chain length is affected by the tension applied to it, and the correction accounts for this effect.
- Correction for Sag: This correction is applied to compensate for the sagging of the chain when it is suspended between two points.
- Correction for Instrumental Errors: This correction accounts for any errors that may occur due to the instrument itself, such as the incorrect reading of the scale or the incorrect setting of the instrument.
- Correction for Human Error: This correction accounts for any errors that may occur due to the surveyor, such as misreading the scale or misjudging the measurement.
- Correction for slope:
Cs = L – D = L (1 – cos Θ) = 2L sin²Θ / 2 (-)
These corrections help to improve the accuracy of the survey results and ensure that the results are reliable and trustworthy.
Traverse survey is a method of surveying where a series of straight lines is connected to form a closed circuit. It is used to determine the positions of points or features along a linear path and to find their relative positions and distances. In a traverse survey, the lengths of the lines and the angles between them are measured, and the positions of points along the traverse are calculated based on these measurements. The traverse survey is commonly used in mapping, construction, and land surveying applications, and it is useful for determining the boundaries of a property, finding the locations of boundaries, and determining the location of man-made and natural features.
Bearing is a method of defining the direction of a line connecting two points, relative to a reference direction. In surveying, bearings are commonly used to describe the direction of a survey line in relation to a known point or reference direction, such as north or magnetic north.
Bearing can be classified into two types:
i. Absolute Bearing: This type of bearing is expressed in degrees from the reference direction, typically true north or magnetic north.
ii. Relative Bearing: This type of bearing is expressed as the angle between the survey line and a known line, such as a previous survey line, with the reference direction being the direction of the known line.
Bearing is a term used in surveying to describe the direction of a line or direction of an object relative to a reference direction. Bearings are typically expressed in degrees and can be classified into two types:
- True Bearings – A true bearing is the horizontal angle between a line and the true north direction.
- Magnetic Bearings – A magnetic bearing is the horizontal angle between a line and the magnetic north direction.
The designation of bearing is important in surveying as it helps to determine the direction of a line in relation to the north direction. This information is useful in determining the location of objects on the earth’s surface and in determining the direction of a line of sight.
In surveying, bearings are used to specify the direction of lines, typically used to connect two points on a map or plan. There are two main systems used for specifying bearings:
- Magnetic Bearings: In this system, bearings are specified with respect to the magnetic North direction.
- True Bearings: In this system, bearings are specified with respect to the True North direction.
Converting from one system to the other requires taking into account the difference between magnetic north and true north, which is known as the Magnetic Declination.
To convert from magnetic bearings to true bearings, the magnetic declination at the location must be added to the magnetic bearing.
To convert from true bearings to magnetic bearings, the magnetic declination at the location must be subtracted from the true bearing.
It’s important to note that the magnetic declination changes over time and space, so it must be up-to-date and accurate for the location in question.
i. Fore Bearing: Fore bearing refers to the horizontal angle measured from a fixed reference direction, such as the north direction, to the line connecting the observer and a distant point. It is used in traverse survey to determine the direction of a line connecting two points.
ii. Back Bearing: Back bearing refers to the horizontal angle measured in the opposite direction of the fore bearing. It is used to check the accuracy of the survey by measuring the angle from the distant point to the observer, which should equal the fore bearing of the line in the opposite direction.
Fore bearing and back bearing are two concepts in traverse survey, which is a method used to measure the horizontal and vertical distances between points to locate them on a map.
Fore bearing refers to the measurement of the angle between the direction of a survey line and the meridian, which is an imaginary line that runs from the North Pole to the South Pole. Fore bearing is taken from the beginning of a survey line and is measured in a clockwise direction.
Back bearing, on the other hand, is the measurement of the angle between the direction of a survey line and the meridian, taken from the end of a survey line. Back bearing is also measured in a clockwise direction.
The relationship between fore bearing and back bearing is that they are 180 degrees apart. In other words, if the fore bearing of a line is X, the back bearing will be X + 180 degrees. This is because a line that starts at one end and ends at another covers the entire 360 degrees circle of a meridian.
- Angles from the given Bearing: In surveying, the direction of a line is often specified by its bearing, which is the angle it makes with a reference direction, usually north. To calculate the angle from the given bearing, we need to know the reference direction and the direction of the line.
- Bearing from the given Angles: To calculate the bearing from the given angle, we need to know the reference direction and the angle between the reference direction and the line. The bearing can be calculated using trigonometry. For example, if we know the angle between the line and north, we can use the formula: bearing = 90 – angle.
i. Prismatic Compass:
A prismatic compass is a type of survey instrument used to determine the direction of a line in relation to magnetic north. It consists of a compass needle mounted in a box-like frame with a sighting mechanism, a scale for measuring the direction, and a mirror for reflecting the scale.
- Measuring direction: The prismatic compass is used to measure the direction of a line in relation to magnetic north.
- Setting out survey lines: The compass can be used to set out survey lines by sighting on a target and rotating the instrument until the magnetic needle is aligned with the magnetic meridian.
- The compass needle is magnetised and suspended within the frame of the instrument.
- The needle aligns itself with magnetic north, allowing the user to read the direction on the scale.
- The sighting mechanism and mirror enable the user to take a sight on a target and align the instrument with the target.
ii. Surveyor’s Compass:
A surveyor’s compass is a type of survey instrument used for determining bearings and azimuths. It consists of a magnetic needle mounted on a rotating dial or plate and a sighting mechanism.
- Measuring direction: The surveyor’s compass is used to measure the direction of a line in relation to magnetic north.
- Setting out survey lines: The compass can be used to set out survey lines by sighting on a target and rotating the dial until the magnetic needle is aligned with the magnetic meridian.
- Measuring angles: The surveyor’s compass can also be used to measure angles by aligning the sighting mechanism with two points and reading the angle on the dial.
- The magnetic needle is suspended within the dial and aligns itself with magnetic north.
- The user rotates the dial until the needle is aligned with the magnetic meridian and reads the direction from the scale.
- The sighting mechanism and rotating dial enable the user to take a sight on a target and align the instrument with the target.
A prismatic compass and a surveyor’s compass are two important instruments used in the field of surveying. The purpose of these compasses is to determine the magnetic bearing of lines or directions. In order to ensure accurate results, it is important to make adjustments to these instruments before using them.
The adjustment of a prismatic compass involves the following steps:
- Levelling the instrument: The prismatic compass must be levelled to ensure that it is in a horizontal position. This is done with the help of a bubble level.
- Setting the magnetic declination: The magnetic declination, which is the difference between magnetic north and true north, must be set correctly in the compass. This can be done by consulting a map or using an online tool.
- Setting the index error: The index error refers to the deviation of the compass needle from the true meridian. It is important to correct this error so that the readings are accurate. This can be done by rotating the compass until the needle points to a known direction, such as the north direction.
The adjustment of a surveyor’s compass is also known as “swing the needle” or “boxing the needle”. The steps involved in this process are:
- Levelling the instrument: Just like the prismatic compass, the surveyor’s compass must also be levelled to ensure that it is in a horizontal position.
- Setting the magnetic declination: The magnetic declination must be set correctly in the surveyor’s compass, just as in the prismatic compass.
- Boxing the needle: This involves rotating the compass in a full circle, noting the maximum and minimum readings of the needle. The difference between these two readings is known as the “box correction”. The correction is applied by rotating the compass plate until the needle points to the average of the maximum and minimum readings.
By making these adjustments, the prismatic compass and surveyor’s compass can be used to accurately determine the magnetic bearing of lines or directions.
The Prismatic Compass and Surveyor’s Compass are two different types of compasses used in land surveying. A Prismatic Compass is a type of magnetic compass that is mounted on a tripod and has a sighting mechanism, which allows the user to take accurate bearings of objects. This type of compass is mainly used for determining the direction of lines and for measuring angles. On the other hand, a Surveyor’s Compass is a type of magnetic compass that is attached to a rod or a staff. It is used to determine the direction of lines, but it is less accurate than the Prismatic Compass. The Surveyor’s Compass is mainly used for rough and quick measurements, while the Prismatic Compass is used for precise and accurate measurements.
The magnetic declination is the angle between the magnetic north and the true north. The Earth’s magnetic field is not aligned with its rotational axis and therefore there is a difference in the direction to magnetic north and true north. The magnetic declination varies from place to place and changes with time. The magnetic declination must be considered in any magnetic compass navigation as it will affect the heading. The magnetic declination can be found from maps, websites or other sources and should be taken into account when conducting surveys or navigation with a magnetic compass.
Magnetic declination is the angle between the magnetic north and the true north. This angle is important in surveying as it affects the measurement of bearings. There are two main variations in declination, which are:
- Annual Variation: This is the change in magnetic declination over time, due to changes in the Earth’s magnetic field. The annual variation can be positive or negative, and the rate of change can vary from year to year.
- Latitudinal Variation: This is the change in magnetic declination as you move from one latitude to another. The latitudinal variation can be positive or negative, depending on the location and the year.
In general, magnetic declination changes as you move across the Earth’s surface, so it is important to correct for these variations when measuring bearings in surveying.
Local Attraction refers to the deviation of the magnetic needle of a compass from its true north direction, due to the presence of magnetic materials in the immediate vicinity of the compass. This phenomenon is known as Local Attraction.
The detection of local attraction is important in surveying to ensure the accuracy of the magnetic bearing measurements. There are several methods to detect local attraction, including:
- Observing the effect of the compass needle while moving around the survey area
- Using a magnetic needle tester to detect the presence of magnetic materials
- Measuring the magnetic field strength with a magnetometer
- Comparing the magnetic bearings taken with a compass with true north bearings taken with a theodolite or GPS.
It is important to correct for local attraction to ensure accurate survey measurements.
i. Chain Triangulation: Chain triangulation is a surveying method that involves using a series of triangles to determine the position and shape of a particular area. This method is based on the principles of triangle geometry, where the angles and distances between the points of a triangle are measured and used to calculate the position and shape of the area.
ii. Survey Station: A survey station is a specific point on a survey line that has been established and marked for the purpose of surveying. Survey stations are used to reference the location of other points in the survey area, and they are typically identified by unique labels or numbers. Survey stations are typically established at regular intervals along the survey line, and they serve as the basis for measurement and data collection during the survey.
Classifying the Survey Lines refers to categorising the different types of survey lines based on their characteristics and purpose. The survey lines used in triangulation are typically classified into two categories:
- Base Lines: These are long, straight survey lines that serve as the foundation for a triangulation network. They are measured with a high degree of precision and accuracy, and they are used to establish the positions of other survey stations.
- Tie Lines: These are shorter survey lines that connect two survey stations and are used to link the triangulation network together. Tie lines are measured less precisely than base lines, as they only need to provide a rough measurement of distance between two points.
Classifying survey lines is an important step in triangulation as it allows surveyors to determine the best approach for measuring each line and to ensure that the measurements are consistent and accurate. This helps to build a robust and reliable triangulation network, which is crucial for mapping and surveying large areas of land.
The conditions to be fulfilled by the survey stations refer to the specific criteria that must be met in order for a survey station to be considered suitable for surveying purposes. These conditions include, but are not limited to:
- Visibility: The station should have a clear line of sight to other stations and points of reference.
- Accessibility: The station should be easily accessible and not be located in hazardous or remote areas.
- Stability: The station should be stable and not be located in areas prone to erosion, landslides, or other types of instability.
- Permanent Mark: The station should be marked with a permanent, identifiable marker such as a bolt or stake.
- Elevation: The station should be located at a known elevation so that the vertical distance between stations can be accurately calculated.
- Reference Points: The station should have reference points nearby that can be used to determine its exact location.
These conditions must be met in order to ensure the accuracy and reliability of the survey data collected from the station.
Locating offsets is a technique used in surveying to find the distance and direction of a point relative to a reference line or station. The procedure of locating offsets is as follows:
- Choose a reference line or station: The first step in locating offsets is to choose a reference line or station. This reference line or station acts as a starting point for finding the offsets.
- Measure the distance and direction: The next step is to measure the distance and direction from the reference line or station to the point of interest. This can be done using a tape or chain and a compass or transit.
- Plot the offset: Once the distance and direction are measured, the offset can be plotted on a map or diagram. This involves drawing a line from the reference line or station to the point of interest, using the measured distance and direction.
- Repeat the process: The process of measuring the distance and direction and plotting the offset can be repeated for multiple points of interest. This helps to create a comprehensive map or diagram of the area being surveyed.
It is important to accurately measure the distance and direction in order to accurately plot the offsets. Any errors in measurement can result in incorrect offsets and therefore, incorrect maps or diagrams.
Chain surveying is a basic and simplest method of surveying that involves using a chain to measure distances between two points. The fieldwork of chain surveying involves the following steps:
- Selection of Survey Stations: The first step is to select the survey stations, which are the points that will be used to conduct the survey. These stations should be easily accessible and visible from a distance.
- Measurement of Baseline: The next step is to measure the base line, which is the main line of the survey and serves as a reference for other measurements. This line is usually measured using a chain or a tape.
- Establishing Survey Stations: After measuring the baseline, the survey stations are established by measuring the offsets from the base line. These offsets are the distances between the survey stations and the base line.
- Measurement of Angles: The angles between the survey lines and the base line are measured using a prismatic compass or a surveyor’s compass.
- Measurement of Distances: The distances between the survey stations are measured using a chain or a tape. It is important to ensure that the chain is straight and taut while measuring the distances.
- Recording Data: All the measurements and observations made during the fieldwork are recorded in a field book for future reference.
- Plotting the Survey: After collecting all the data, the survey is plotted on a map or a plan, using a scale and the appropriate symbols. The survey stations, survey lines, and angles are plotted on the map or plan.
These are the steps involved in the fieldwork of chain surveying. It is important to ensure accuracy and precision in each step to ensure the reliability of the survey.
i. Cross Staff: The cross staff is an instrument used in surveying to determine angles and directions. It is a simple device that consists of a rod or staff with a perpendicular cross piece that is used to sight objects and measure angles. The cross staff is used in combination with a compass or a theodolite to determine the direction of objects relative to the surveyor.
ii. Prism Square: The prism square is a device used in surveying to measure angles and directions. It consists of a square frame with a prism attached at the centre, which is used to reflect light to the surveyor’s eye. The prism square is used in combination with a theodolite or a total station to measure angles and directions, and is particularly useful for measuring vertical angles and for aligning survey equipment.
iii. Optical Square: The optical square is a device used in surveying to measure angles and directions. It is similar to the prism square but instead of using a prism, it uses a pair of mirrors to reflect light to the surveyor’s eye. The optical square is used in combination with a theodolite or a total station to measure angles and directions, and is particularly useful for measuring vertical angles and for aligning survey equipment.