Linear Measurement PDF

ASC-111 Surveying and Levelling Linear Measurements Presented by Course Instructors: ANKITA SHINDE Dr. Jitendra Rajput Roll No: 12818 Dr. D. K. Singh Ph.D. II Yea...

ASC-111 Surveying and Levelling Linear Measurements Presented by Course Instructors: ANKITA SHINDE Dr. Jitendra Rajput Roll No: 12818 Dr. D. K. Singh Ph.D. II Year Soil and Water Conservation Engineering Division of Agricultural Engineering, ICAR-Indian Agricultural Research Institute, New Delhi, 110012 1  LINEAR MEASUREMENTS DIFFERENT METHODS DIRECT MEASUREMENTS Content INSTRUMENTS FOR CHAINING of RANGING OUT SURVEY LINES Linear Measurements CHAINING  Introduction Linear measurement is the process of measuring the distance between two points 01 or objects along a straight line It can also be defined as the gap between the leftmost end and the rightmost end. 02 Linear measure refers to measurements that are directly proportional to the 03 distance traveled along the axis of the measurement Different Methods of Linear Measurements Direct Measurements 01 Measurements by Optical Means 02 Electromagnetic Method 03 4  Direct Method of Linear Measurement In direct method of linear measurements, the distance is measured between two points with the instruments by being present at the location of the point itself. Let’s assume we want to measure the distance between any two points A & B which is some Millimeters/Meters/Kilometers away from each other then we need to measure the distance by moving from one point to another with any suitable instrument. The purpose is to take readings to have precise knowledge about the distance so that we may plan other activities according to that. Direct Measurement Methods 01 Pacing PASSOMETER 02 03 PEDOMETER Odometer 04 Speedometer 05 Chaining  1. Pacing  It is mostly applied in preliminary surveys by walking a certain distance to get a rough idea.  It is a reasonably easy and quick method of measuring distance in the field.  In this method, the number of steps is counted as a unit, and the total number of steps is taken into consideration.  2. Passometer  It is a watch-like instrument that is carried by the person.  It records steps while movement and gives a more accurate idea.  3. Pedometer  It is similar to a pedometer, but it measures the distance.  It is good at measuring vertical distances.  4. Odometer and Speedometer  Odometer: Measures the total distance traveled by a vehicle  It measures the number of revolutions, and by that, it measures the distance.  Speedometer: Measures the current speed of a vehicle.  Generally, it is installed in vehicles to measure the distance.  5. Chains and Tapes  These are used to do the work more accurately on a large scale.  Generally, chains are available in two lengths- 20 m and 30 m..  Instruments used for chain surveying: The various instruments used in chain surveying are as follows. Chains Arrows Pegs ranging rods offset rods plumb bob  1. CHAINS 1.Gunter’s Chain (or Surveyor’s Chain): The most traditional and widely used chain, particularly in land surveying. It is 66 feet long and consists of 100 links, each measuring 0.66 feet (7.92 inches). This chain was designed to easily convert measurements into acres (since 10 square Gunter chains equal one acre). 2. Engineer’s Chain:  This chain measures 100 feet in length and consists of 100 links, each link being 1 foot long.  It is commonly used in engineering and construction projects in the United States and is preferred when measurements need to align directly with the imperial system in feet and inches. 3. Revenue Chain: Primarily used in land revenue surveys, this chain is 33 feet long, with each link measuring 0.66 feet. Its shorter length is convenient for land measurements over smaller areas and is often used in rural or agricultural land assessment. The most traditional and widely used chain, particularly in land surveying. 4. Metric Chain: Designed for use in countries using the metric system, metric chains are typically available in lengths of 20 meters or 30 meters. A 20-meter chain has 100 links (each 0.2 meters or 20 centimeters), and a 30-meter chain has 150 links (each also 0.2 meters). Metric chains are commonly used in engineering and construction outside of the United States. The most traditional and widely used chain, particularly in land surveying. 5. Steel Band or Band Chain:  Unlike traditional chains, the steel band chain is made of a steel strip rather than linked metal.  Typically, steel bands come in 20-meter and 30- meter lengths.  They are more flexible, lightweight, and accurate than link chains and are used when high precision is required.  2. TAPES 1.Cloth or Linen Tape:  Made of linen or cloth and often reinforced with brass or copper wires,  this tape is light and flexible, making it easy to carry and use on rough terrain.  However, it tends to stretch and wear out over time, reducing measurement accuracy, so it’s mainly used for approximate measurements. 2. Steel Tape: Steel tapes are made of high-quality steel, providing a high level of accuracy and durability. They are commonly used in surveying where precise measurements are required. Steel tapes can come in lengths of 15, 20, 30, or 50 meters (or equivalent feet) and are marked in metric or imperial units. However, they are prone to rust and can be damaged if bent sharply 3. Invar Tape:  Made from a nickel-steel alloy called Invar, this tape has a very low coefficient of thermal expansion, making it highly resistant to temperature-induced length changes.  Invar tapes are used for precise measurements in applications requiring extremely high accuracy, such as baseline measurements in geodetic surveys.  3. ARROWS  In surveying, arrows (also called marking pins or chain pins) are metal pins used to mark intervals along a survey line during chaining or tape measurements.  Arrows play a crucial role in maintaining accuracy, especially over long distances, by allowing surveyors to track cumulative measurements without losing alignment or reference points.  4. PEGS  In surveying, pegs are small wooden or metal stakes used to mark specific points on the ground.  These are essential tools for establishing and maintaining reference points in the field, helping surveyors to identify and demarcate boundaries, control points, or other critical locations in a survey area.  5. Ranging Rods  Ranging rods (or ranging poles) are essential tools used to visually align points and help surveyors establish straight lines over a distance.  These rods provide clear, vertical markers that allow surveyors to sight lines accurately and keep measurements straight, especially when working over uneven terrain or longer distances.  Typically, ranging rods are around 2 to 3 meters (6 to 10 feet) long.  6. OFFSET RODS  In surveying, offset rods are specialized tools used to measure short, perpendicular distances (known as offsets) from a survey line to specific features or points of interest, such as boundaries, buildings, or obstacles.  Offset rods are primarily used to measure perpendicular (right- angle) distances from a survey line to an object or point that needs to be recorded. This is essential for mapping objects that do not lie directly on the main survey line.  They are typically around 3 to 4 meters.  7. PLUMB BOB  In surveying, a plumb bob is a simple but essential tool used to establish a vertical reference line.  It consists of a weight, typically conical or cylindrical, suspended from a string.  This tool operates on the principle of gravity, aligning itself perfectly vertical when at rest, making it invaluable for accurate vertical alignment and transferring points between levels.  Ranging out Survey Lines Ranging out survey lines is a fundamental process in surveying used to establish a straight line between two or more points over a distance. This technique is essential for accurate measurements, particularly in land surveying, construction layout, and boundary marking. The goal of ranging is to ensure that intermediate points between the starting and ending points lie in a straight line, which helps in maintaining measurement accuracy. 27  Methods of Ranging Direct Ranging 01 Indirect Ranging 02 1. Direct Ranging: Used when both endpoints of the line are visible. The surveyor can sight from one end to the other without needing additional rods or intermediate steps.  Methods of Ranging Direct Ranging 01 Indirect Ranging 02 2. Indirect (Reciprocal Ranging): Used when endpoints are not visible from each other, such as when there are hills, buildings, or other obstructions in the way. The surveyor uses reciprocal sightings from intermediate points, adjusting until the endpoints are visually aligned through the intermediate points.  Error due to Incorrect chain Causes of Incorrect Chain Length: Temperature Variations: Chains expand in hot weather and contract in cold weather. This can affect measurements if chains aren’t adjusted or calibrated for temperature. Wear and Tear: Chains or tapes can stretch or shrink over time due to use, tension, or exposure to environmental conditions. Manufacturing Defects: Chains may sometimes come with slight inaccuracies due to imperfections from manufacturing. Incorrect Calibration: Chains that are not regularly checked and calibrated may deviate from their nominal lengths. 31  Types of Error due to Incorrect chain 1. Error Due to Chain Length Being Too Long:  When a chain is longer than its nominal length (e.g., a 20-meter chain that has stretched to 20.1 meters), it will measure distances as shorter than they actually are.  This is called a negative error since the true length is longer than the measured length.  Impact: The distance measured will be underestimated, and calculated areas may also be smaller than their true size. 32  Types of Error due to Incorrect chain 1. Error Due to Chain Length Being Too Short:  When a chain is shorter than its nominal length (e.g., a 20-meter chain that has shrunk to 19.9 meters), it will measure distances as longer than they actually are.  This is called a positive error since the true length is shorter than the measured length.  Impact: The distance measured will be overestimated, and calculated areas may also be larger than their actual size. 33 Correction to Measured Length 34 EXAMPLES EXAMPLES  If the chain is too long: Measured distance will be less than the true distance, so add the correction factor. If the chain is too short: Measured distance will be more than the true distance, so subtract the correction factor. Assignment