Levelling

Levelling

Contents

Define the following terms: i. Levelling ii. Level Surface and Level Line iii. Horizontal Plane and Horizontal Line iv. Datum and Elevation v. Mean Sea Level and Bench Mark 2

Recall the methods of Levelling 2

Describe various types of levels used in the levelling 5

Recall types of Levelling Staffs used in the Levelling 6

Recall Temporary Adjustments of the Levelling 7

Define and classify Direct Levelling 8

Define the following terms: i. Station ii. Height of Instrument iii. Back-sight and Fore-sight iv. Intermediate Station v. Turning Point 9

Recall Steps followed in Levelling 10

Describe the following methods of computing the Levels: i. Height of Instrument or Collimation method ii. Rise and Fall method 11

Compare Collimation method with Rise and Fall Method 12

Recall Balancing of Back-sights and Fore-sights 13

Recall Balancing of Sight on a Slope 14

Describe the effect of Curvature and Refraction in Levelling 15

Recall following types of Levelling: i. Simple Levelling ii. Differential Levelling iii. Profile Levelling iv. Cross-section Levelling v. Reciprocal Levelling vi. Hypsometry Levelling 16

Describe the Functions of Level Tube 17

Describe the Sensitiveness of Level Tube 18

Define the following terms: i. Levelling ii. Level Surface and Level Line iii. Horizontal Plane and Horizontal Line iv. Datum and Elevation v. Mean Sea Level and Bench Mark

i. Levelling: Levelling is the process of determining the relative height or elevation of points on the surface of the earth. This is typically done by using a surveying instrument such as a level or a total station, and the results are used to create a topographic map or a contour map of the area being surveyed.

ii. Level Surface and Level Line: A level surface is a surface that is horizontal and perpendicular to the direction of gravity. A level line is a line that is parallel to the direction of gravity and passes through a point at the same height as a given reference point.

iii. Horizontal Plane and Horizontal Line: A horizontal plane is a plane that is perpendicular to the direction of gravity. A horizontal line is a line that is parallel to the direction of gravity.

iv. Datum and Elevation: A datum is a fixed reference point used as a starting point for determining elevations or heights. Elevation is the vertical distance of a point from a given datum, typically measured in meters or feet.

v. Mean Sea Level and Bench Mark: Mean Sea Level (MSL) is a term used to describe the average height of the sea surface, measured over a long period of time. Bench Mark (BM) is a term used to describe a permanent and stable reference point that is used as a starting point for determining elevations. BM’s are usually marked on concrete pillars or on the ground and are usually identified by a metal tag or disk. The elevation of a BM is typically referenced to MSL and is used as a starting point for measuring elevations of other points in a survey.

Recall the methods of Levelling

Levelling is the process of determining the relative height or elevation of points on the surface of the earth. There are several methods of levelling that are used in surveying, including:

  1. Direct levelling: It is the most commonly used method of levelling. In this method, measurements are observed directly from the levelling instrument. Based on the observation points and instrument positions direct levelling is divided into different types as follows:
  • Simple levelling
  • Differential levelling
  • Fly levelling
  • Profile levelling
  • Precise levelling
  • Reciprocal levelling
  1. Differential Levelling

Differential levelling is performed when the distance between two points is more. In this process, a number of inter stations are located and instruments are shifted to each station and observed the elevation of inter station points. Finally the difference between the original two points is determined.

Fly Levelling

Fly levelling is conducted when the benchmark is very far from the workstation. In such a case, a temporary bench mark is located at the workstation which is located based on the original benchmark. Even though it is not highly precise it is used for determining approximate level.

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  1. Simple Levelling: It is a simple and basic form of levelling in which the levelling instrument is placed between the points at which elevation is to be found. Levelling rods are placed at that point and sighted through a leveling instrument. It is performed only when the points are nearer to each other without any obstacles.

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Profile Levelling
Profile leveling is generally adopted to find elevation of points along a line such as for road, rails or rivers etc. In this case, readings of intermediate stations are taken and a reduced level of each station is found. From this cross section of the alignment is drawn
In summary, there are several methods of levelling that are used in surveying, including spirit level levelling, optical levelling, digital levelling, trigonometric levelling, and barometric levelling. Each method has its own advantages and disadvantages, and the choice of method will depend on the specific requirements of the survey.

Describe various types of levels used in the levelling

Levelling is a technique used in surveying to determine the relative height or elevation of different points on the ground. It involves using a levelling instrument, such as a level or a theodolite, to measure the vertical distance between two points. The accuracy of levelling depends on the quality of the levelling instrument used. There are various types of levels used in levelling, which can be classified as follows:

  1. Dumpy level: A dumpy level is a simple levelling instrument consisting of a telescope mounted on a tripod. The telescope is used to sight a staff placed at the point whose elevation is to be determined. The dumpy level is equipped with a spirit level to ensure that the instrument is level before taking measurements. A dumpy level is typically used for low-accuracy work, such as construction.
  2. Automatic level: An automatic level is a more advanced levelling instrument that uses a compensator to automatically level the instrument. The compensator contains a prism and a pendulum that maintain the level of the telescope even if the instrument is tilted. Automatic levels are commonly used in construction, engineering, and surveying.
  3. Digital level: A digital level is a modern levelling instrument that uses electronic sensors to measure the height difference between two points. Digital levels are very precise and provide accurate measurements in real-time. They are commonly used in high-precision applications, such as engineering and construction.
  4. Laser level: A laser level is a levelling instrument that uses a laser beam to project a straight line on a surface. The laser level is mounted on a tripod and can be rotated to project a line in any direction. Laser levels are commonly used in construction and interior decoration.
  5. Total station: A total station is a multifunctional instrument that combines a theodolite with a distance-measuring device, such as a laser rangefinder or an EDM (electronic distance measurement) system. Total stations can measure angles, distances, and elevations with high accuracy and are commonly used in engineering, construction, and land surveying.

In summary, there are various types of levels used in levelling, including dumpy levels, automatic levels, digital levels, laser levels, and total stations. The choice of level depends on factors such as the accuracy required, the type of application, and the environmental conditions. It is important for surveyors to be familiar with these different types of levels to ensure accurate and reliable measurements.

Recall types of Levelling Staffs used in the Levelling

A levelling staff, also known as a levelling rod or range pole, is a measuring device used in levelling to determine the height or elevation of a point relative to a reference point. There are several types of levelling staffs used in levelling, including:

  1. SOLID STAFF: A solid staff is a type of levelling staff used in surveying to measure the height difference between two or more points on the ground. Unlike telescopic staffs, which can be adjusted to different heights, a solid staff has a fixed height and is usually made of a single piece of material, such as wood or aluminium. Solid staffs are typically marked with graduations to indicate the height of the point being surveyed. They are commonly used in low-precision applications, such as construction and building layout.
  2. Telescopic Staff: A telescopic staff is a rod that can be extended and locked into place at different lengths. Telescopic staffs have graduations along their length and are commonly used for intermediate-distance levelling, such as determining the elevation of a building site or a road.
  3. Folding Rule Staff: A folding rule staff is a rod that is made up of several sections that can be folded up for storage and transport. Folding rule staffs have graduations along their length and are commonly used for short-distance levelling, such as determining the height of a building or a tree.

In summary, there are several types of levelling staff used in levelling, including fixed graduated staff, telescopic staff, mini prism pole, and folding rule staff. Each type of levelling staff has its own advantages and disadvantages, and the choice of staff will depend on the specific requirements of the survey.

Recall Temporary Adjustments of the Levelling

Temporary adjustments are modifications made to a levelling instrument to ensure accurate measurements during a levelling survey. There are several temporary adjustments that can be made to a levelling instrument, including:

  1. Centring Adjustment: The centring adjustment is used to ensure that the axis of the levelling instrument is centred over the tripod head. This adjustment is important to make when using a dumpy level or an auto level to ensure that the instrument is correctly centred.
  2. Elimination of parallax: Parallax is the apparent shift in the position of an object when viewed from different angles. When observing distant objects, such as stars, the Earth’s movement around the sun causes a shift in the object’s apparent position. This shift is known as parallax.

Eliminating parallax involves measuring the angle of the object’s apparent shift from two different positions and using trigonometry to calculate the object’s distance. This technique is commonly used in astronomy to determine the distance to nearby stars.

  1. Levelling of instrument: Levelling of an instrument is a process used in surveying and engineering to determine the relative heights or elevations of points on the Earth’s surface. The instrument used in levelling is a level, which consists of a telescope that is mounted on a tripod and equipped with a spirit level.

During the levelling process, the level is set up at a known elevation, and then the telescope is pointed towards a rod held at the point to be measured. The rod has markings on it that correspond to different elevations. The surveyor then reads the height on the rod through the telescope and records the measurement. This process is repeated at different points, and the data is used to create a level line or contour line.

In summary, temporary adjustments are modifications made to a levelling instrument to ensure accurate measurements during a levelling survey. Some of the temporary adjustments include focus adjustment, collimation adjustment, bubble adjustment, plumb adjustment, and centring adjustment. Making these temporary adjustments is important to ensure the accuracy of the levelling measurements.

Define and classify Direct Levelling

Direct Levelling is a method used to determine the difference in elevation between two points. It is commonly used in land surveying to measure the height of an object or the slope of a surface.

Classification of Direct Levelling:

  1. Plane Levelling: This type of levelling involves measuring the difference in elevation between two points that are in the same horizontal plane.
  2. Differential Levelling: This type of levelling involves measuring the difference in elevation between two points that are not in the same horizontal plane.
  3. Trigonometric Levelling: This type of levelling involves using trigonometry to calculate the difference in elevation between two points that are not in line of sight.
  4. Barometric Levelling: This type of levelling uses atmospheric pressure to determine the difference in elevation between two points.
  5. Reciprocal levelling: Reciprocal levelling is a technique used in surveying to check the accuracy of levelling measurements. It involves taking measurements in two directions, with the staff placed at each end of a survey line. The instrument is then moved to the opposite end of the line, and the measurements are taken again in the opposite direction.

In conclusion, Direct Levelling is an important method in land surveying that is used to accurately determine the difference in elevation between two points. There are several types of direct levelling, each with its own unique method and application.

Define the following terms: i. Station ii. Height of Instrument iii. Back-sight and Fore-sight iv. Intermediate Station v. Turning Point

  1. Station: A station in surveying refers to a fixed reference point with a known elevation. It is used as a starting point or benchmark for measuring elevations of other points.
  2. Height of Instrument: The height of instrument refers to the vertical distance from the ground level to the level of the surveying instrument. This measurement is used to determine the difference in elevation between two points.
  3. Back-sight: A back-sight in surveying refers to a measurement taken from a known elevation to a lower elevation point. The back-sight is used to establish the starting elevation for a series of measurements.
  4. Fore-sight: A fore-sight in surveying refers to a measurement taken from a known elevation to a higher elevation point. The fore-sight is used to determine the difference in elevation between two points.
  5. Intermediate Station: An intermediate station in surveying refers to a point between two stations that is used to help determine the elevation difference between the two stations.
  6. Turning Point: A turning point in surveying refers to a point where the direction of measurement changes. It is used to help determine the difference in elevation between two points that are not in line of sight.

Recall Steps followed in Levelling

The steps involved in levelling are:

  1. Setting up the Instrument: This step involves choosing a suitable location to set up the surveying instrument and determining the height of the instrument.
  2. Establishing the Benchmark: A benchmark is a reference point with a known elevation. The benchmark is used to determine the elevations of other points. The first step in levelling is to establish the benchmark.
  3. Taking Back-sights and Fore-sights: Back-sights are measurements taken from a known elevation to a lower elevation point, while fore-sights are measurements taken from a known elevation to a higher elevation point. These measurements are used to determine the difference in elevation between two points.
  4. Computing Elevations: After taking the back-sights and fore-sights, the elevations of each point can be computed by adding or subtracting the difference in elevation to the elevation of the benchmark.
  5. Adjusting for Instrument Errors: Some errors can occur during the levelling process due to the imperfections in the surveying instrument. These errors can be corrected by adjusting the readings taken with the instrument.
  6. Recording Results: The results of the levelling process should be recorded in a clear and organised manner to ensure that they can be easily referenced in the future.
  7. Checking Results: After the results have been recorded, they should be checked to ensure that they are accurate and that any errors have been corrected.

In conclusion, levelling is a step-by-step process that involves setting up the instrument, establishing the benchmark, taking back-sights and fore-sights, computing elevations, adjusting for instrument errors, recording results, and checking results.

Describe the following methods of computing the Levels: i. Height of Instrument or Collimation method ii. Rise and Fall method

  1. Height of Instrument or Collimation Method: The Height of Instrument or Collimation method is a method of computing elevations in which the height of the surveying instrument is used to determine the difference in elevation between two points. In this method, the difference in elevation is calculated by measuring the vertical angle from the height of the instrument to the point of interest and then using trigonometry to determine the difference in elevation.
  2. Rise and Fall Method: The Rise and Fall method is a method of computing elevations in which the difference in elevation between two points is determined by measuring the vertical angle between the points. In this method, the difference in elevation is calculated by measuring the vertical angle between the two points and then using trigonometry to determine the difference in elevation.

Both the Height of Instrument or Collimation method and the Rise and Fall method are commonly used in surveying to determine the difference in elevation between two points. The choice between these methods often depends on the specific requirements of the survey and the type of information that needs to be obtained.

Compare Collimation method with Rise and Fall Method

The Collimation method and the Rise and Fall method are two methods used in surveying to determine the difference in elevation between two points. The main difference between these two methods is the reference point used to determine the difference in elevation.

In the Collimation method, the height of the surveying instrument is used as a reference point. The vertical angle from the height of the instrument to the point of interest is measured and then used to determine the difference in elevation using trigonometry. This method is useful when the elevation of the surveying instrument is known and can be used as a reference point.

In the Rise and Fall method, the difference in elevation between two points is determined by measuring the vertical angle between the two points. The difference in elevation is calculated by using trigonometry to determine the angle and then applying the angle to determine the difference in elevation. This method is useful when the elevations of both points are unknown and a reference point is not available.

Both methods have their own advantages and disadvantages. The Collimation method is more accurate when the height of the instrument is known, but it requires a stable and well-calibrated instrument. The Rise and Fall method is less dependent on the instrument and does not require a known reference point, but it may be less accurate due to the difficulty in measuring vertical angles accurately.

In conclusion, both the Collimation method and the Rise and Fall method have their own strengths and weaknesses, and the choice between these methods depends on the specific requirements of the survey and the type of information that needs to be obtained.

Recall Balancing of Back-sights and Fore-sights

Balancing of Back-sights and Fore-sights is an important process in levelling that helps to ensure the accuracy and reliability of the elevation measurements. The process of balancing involves comparing the sum of the back-sight and fore-sight readings taken at a station to the known elevation of the station. If the sum of the readings does not match the known elevation, then adjustments must be made to one or both of the readings.

Back-sights and fore-sights are readings taken when surveying a levelling profile. A back-sight is the first reading taken at a station and is taken in the direction of the preceding station. A fore-sight is the final reading taken at a station and is taken in the direction of the next station.

Balancing of back-sights and fore-sights is typically done by adjusting the height of the instrument, also known as the height of collimation. The height of the instrument is adjusted until the sum of the back-sight and fore-sight readings match the known elevation of the station.

Balancing of back-sights and fore-sights is important because it helps to ensure that the elevation measurements are accurate and reliable. If the back-sight and fore-sight readings are not balanced, then the elevation measurements may be incorrect, which could result in errors in the final survey results.

In conclusion, balancing of back-sights and fore-sights is a crucial process in levelling that helps to ensure the accuracy and reliability of the elevation measurements. By comparing the sum of the readings to the known elevation of the station and making adjustments as needed, the surveyor can ensure that the elevation measurements are accurate and reliable.

Recall Balancing of Sight on a Slope

Balancing sight on a slope refers to the process of adjusting the sight on a firearm to account for the effects of gravity and air resistance when shooting at a target that is either uphill or downhill from the shooter’s position. This process is necessary to ensure that the bullet hits the target accurately and consistently, especially when the slope is steep or the target is far away.

The following are the steps involved in balancing sight on a slope:

  1. Determine the slope angle: To balance sight on a slope, the shooter must first determine the angle of the slope. This can be done using a clinometer or a slope finder.
  2. Adjust the sight: Based on the slope angle, the shooter must adjust the sight accordingly. If the target is uphill, the sight should be raised, while if the target is downhill, the sight should be lowered. The amount of adjustment required depends on the slope angle and the distance to the target.
  3. Check the trajectory: After adjusting the sight, the shooter must check the trajectory of the bullet to ensure that it hits the target accurately. This can be done by observing the trajectory of the bullet as it travels through the air or by using a trajectory simulation tool.
  4. Adjust as needed: If the trajectory of the bullet is not as expected, the shooter must make further adjustments to the sight to ensure that the bullet hits the target accurately. This process may need to be repeated several times until the desired accuracy is achieved.

In summary, balancing sight on a slope is an essential aspect of shooting accuracy and requires a good understanding of the effects of gravity and air resistance on the trajectory of a bullet. The process involves determining the slope angle, adjusting the sight accordingly, checking the trajectory, and making further adjustments as needed.

Describe the effect of Curvature and Refraction in Levelling

Levelling is a surveying technique used to determine the height or elevation of a point relative to a reference level. The effect of curvature and refraction on levelling can impact the accuracy of these measurements.

  1. Effect of Curvature: The earth is not a flat surface, but rather a sphere with a curved surface. This curvature can affect the accuracy of levelling measurements, especially when measuring long distances. The curvature of the earth causes the line of sight between the levelling instrument and the target to be slightly curved, which can result in an error in the measurement. To mitigate this error, a correction factor for the curvature of the earth must be applied to the levelling measurement.
  2. Effect of Refraction: Refraction is the bending of light as it passes through different media with different refractive indices. In levelling, refraction occurs when the light from the levelling instrument passes through the air to reach the target. This bending of light can cause the line of sight to be slightly distorted, which can result in an error in the measurement. To mitigate this error, a correction factor for refraction must be applied to the levelling measurement.

In conclusion, the effects of curvature and refraction on levelling can have a significant impact on the accuracy of these measurements. To ensure accurate levelling measurements, it is important to take these effects into consideration and apply the appropriate correction factors.

Recall following types of Levelling: i. Simple Levelling ii. Differential Levelling iii. Profile Levelling iv. Cross-section Levelling v. Reciprocal Levelling vi. Hypsometry Levelling

  1. Simple Levelling: Simple levelling is a surveying method used to determine the difference in height between two points. It involves setting up a levelling instrument (such as a spirit level) at a known point and measuring the height difference to another point. The process is repeated for multiple points to obtain the elevation of each point relative to a reference point, usually a benchmark.
  2. Differential Levelling: Differential levelling is a type of surveying method used to determine the difference in height between two points by observing the difference in reading between two setups. In this method, a series of observations is taken along a level line, with the instrument set up at two different points and the height difference being determined by the difference in the readings taken at each setup.
  3. Profile Levelling: Profile levelling is a type of surveying method used to determine the elevation of a series of points along a line. It is often used to obtain the elevation of points along a roadway, canal, or other linear structure. In this method, the instrument is set up at one point and a series of observations is taken along the line, determining the height difference of each point relative to the starting point.
  4. Cross-section Levelling: Cross-section levelling is a type of surveying method used to determine the elevation of points across a section of land. In this method, a series of levelling observations is taken along two perpendicular lines, forming a grid pattern, to determine the elevation of each point within the grid. The process is repeated for multiple sections to obtain a complete topographical map of the area.
  5. Reciprocal Levelling: Reciprocal levelling is a type of surveying method used to determine the difference in height between two points by observing the change in reading between two setups, with one setup being used as a reference and the other being used as a verifying setup. In this method, the instrument is set up at one point, observations are taken at another point, and the instrument is then set up at the second point to verify the readings taken at the first setup.
  6. Hypsometry Levelling: Hypsometry levelling is a type of surveying method used to determine the elevation of points relative to a reference level, such as mean sea level. It involves making precise levelling observations along a network of level lines, with the elevations being determined by the difference in height between each point and the reference level. The resulting elevations are then used to create a topographical map of the area, with contours being used to represent the elevation changes.

Describe the Functions of Level Tube

A level tube is a device used in process control and instrumentation to measure the level of liquid in a tank, vessel or other container. The functions of a level tube are:

  1. Liquid Level Measurement: The main function of a level tube is to measure the liquid level within a container. This measurement is important for process control and safety as it ensures that the liquid level remains within acceptable limits.
  2. Overflow Protection: A level tube can be used as a means of overflow protection to prevent liquid from spilling out of the container. This is important to prevent environmental damage or contamination.
  3. Inventory Management: A level tube can be used to manage inventory levels by indicating the amount of liquid stored in a container. This information can be used to schedule deliveries and monitor consumption rates.
  4. High/Low-Level Alarms: A level tube can be equipped with high and low-level alarms that trigger an alarm when the liquid level reaches a predetermined threshold. This is important for process control and safety as it alerts operators to potential overflow or low-level conditions.
  5. Control Input: A level tube can be used as an input for control systems, such as pump control or solenoid valve control. The level measurement can be used to control the flow of liquids into or out of the container, maintaining the desired liquid level.

Overall, the functions of a level tube are essential in ensuring that the liquid level within a container is accurately measured, managed, and controlled, providing a high level of safety and process control in various industrial applications.

Describe the Sensitiveness of Level Tube

The sensitiveness of a level tube refers to its ability to accurately measure the level of liquid in a container. The following are the factors that affect the sensitiveness of a level tube:

  1. Liquid Properties: The properties of the liquid being measured can affect the sensitiveness of a level tube. For example, liquids with high viscosity or surface tension can cause changes in the level measurement that are not representative of the actual liquid level.
  2. Temperature: Changes in temperature can cause the liquid level to expand or contract, affecting the accuracy of the level measurement. The level tube must be able to accurately measure the level despite these changes.
  3. Vibrations: Vibrations from equipment, pumps, or other sources can cause changes in the level measurement that are not representative of the actual liquid level. The level tube must be designed to withstand these vibrations.
  4. Tank Configuration: The configuration of the tank or container can affect the level measurement. For example, an irregularly shaped container can cause variations in the level measurement that are not representative of the actual liquid level.
  5. Installations: The way the level tube is installed can also affect its sensitiveness. For example, a level tube installed near a pump or other source of vibration may be less sensitive than one installed in a location with minimal vibrations.
  6. Calibration: Regular calibration of the level tube is necessary to ensure its accuracy. The level tube should be calibrated to the specific conditions of the application, including the liquid properties, temperature, and other factors that may affect its accuracy.

In conclusion, the sensitiveness of a level tube is a critical factor in its ability to accurately measure the level of liquid in a container. The level tube must be designed and installed to withstand various factors that can affect its accuracy, and it must be regularly calibrated to maintain its accuracy over time.