Linear Measurement and Chain Surveying: Methods and Equipment

Linear Measurement and Chain Surveying: Methods and Equipment

Dear readers, measuring the distance between two points is the most fundamental task in land surveying, known as Linear Measurement. To prepare a map, Horizontal Distances are always required. In today's article, we will discuss the various methods and equipment used for measuring distance.

Methods of Linear Measurement

Distance measurement techniques can be primarily categorized into four groups:

(A) Approximate Methods

These methods are used during Reconnaissance surveys or to perform quick "sanity checks" to detect large blunders in chain measurements.

• Pacing: Calculating distance by counting the number of steps taken (1 step ≈ 0.75 - 0.8 meters).

• Passometer: A pocket-sized device that automatically counts the number of steps taken.

• Pedometer: Similar to a passometer, but it is calibrated to record the actual distance instead of just the number of steps.

• Odometer: A device attached to a wheel that measures distance based on the number of wheel rotations.

• Speedometer: An instrument found in vehicles that directly displays the distance traveled.

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(B) Measurement using linear measurement

Methods of Linear Measurement

Distance can be measured in three primary ways depending on the required precision:

• Direct Method: Distances are measured directly on the ground using chains or tapes.

• Optical Method: Distances are calculated using optical instruments like a Tacheometer or Theodolite (without physically stretching a tape between points).

• Electronic Method: Using modern Electronic Distance Measurement (EDM) tools, Total Stations, or GPS.

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Common Tools for Direct Measurement

To perform a professional survey, several small but vital instruments are used alongside the chain:

Equipment	Purpose
Chain / Tape	To measure the actual linear distance.
Arrows	To mark the end of each chain length on the ground.
Ranging Rods	To align the survey line between two distant stations.
Offset Rods	To measure small lateral distances (offsets) from the main line.
Plumb Bob	To transfer points vertically to the ground (essential on sloping terrain).
Pegs	To permanently or semi-permanently mark station points.

This is the most accurate and common method in surveying, known as Chaining.

Types of Chains

In India, various types of chains are used based on the specific requirements of the project:

1. Metric Chain: Most commonly used today. Available in lengths of 20m and 30m.

   • Note: A 20m chain has 100 links, while a 30m chain has 150 links (each link is 20cm), tallies are provided every 2 meters.

   • Steel Band: Also called a Band Chain. It consists of a long ribbon of blue steel and is more accurate than a regular link chain because its length does not change due to the wearing of rings.

   • Chains are made of galvanized mild steel wires connected by circular or oval rings. They feature Brass Tallies at regular intervals for easy reading.

2. Gunter’s Chain (Surveyor’s Chain): 66 feet long with 100 links. It is very convenient for measuring area in acres (10 square chains = 1 acre).

3. Engineer’s Chain: 100 feet long with 100 links (1 link = 1 foot).

4. Revenue Chain: 33 feet long with 16 links. Primarily used for cadastral (property) surveys.

Types of Tapes

Tapes are classified into four types based on the material used in their construction:

1. Linen or Cloth Tape: Lightweight and flexible, but prone to shrinking due to moisture and stretching when pulled.

2. Metallic Tape: Made of linen reinforced with woven brass or copper wires. This is the most popular choice for general field surveys as it combines durability with flexibility.

3. Steel Tape: Highly accurate but delicate. It is susceptible to rusting and can snap if kinked (regular oiling and careful handling are mandatory).

4. Invar Tape: Made from an alloy of Nickel (36%) and Steel. It has a very low coefficient of thermal expansion, making it the most accurate and expensive tape. It is used for high-precision baseline measurements.

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Standard Conventional Signs

At the conclusion of a survey, specific symbols are used to represent objects (such as wells, roads, or temples) on a map. These standard conventions ensure that any person can easily interpret the technical drawing.

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NTS Study Note: A frequent exam question is: "Which is the most accurate tape?" Always remember, Invar Tape is renowned for its extreme precision and is used for primary triangulation baselines.

🏗️ Surveying: Complete Study Guide & Index

📔 Part 1: Fundamentals of Surveying

• Surveying: A Bird's Eye View – Meaning and significance of land surveying.

• Fundamental Principles – Classification and types of surveying.

• Primary Division – Understanding Plane vs. Geodetic Surveying.

• Representative Fraction (RF) – Utilization of scales and reduction factors.

📏 Part 2: Linear Measurement & Chain Survey

• Chain Surveying – Basic procedures and workflow.

• Errors & Adjustments in Chaining – Deficiencies in measurement and their remedies.

• Distance Measurement Methods – Detailed discussion on linear surveying tools.

• Tape Corrections – Adjustments for Sag, Temperature, and Pull.

🧭 Part 3: Angular & Instrumental Survey

• Compass Surveying – Magnetic bearing survey and its applications.

• Plane Table Surveying – Equipment used and graphical methods.

• Theodolite Surveying – Horizontal and vertical angle measurement.

• Total Station – Components, features, and modern digital use.

🏔️ Part 4: Levelling & Elevation

• Need for Levelling – Why vertical measurement is vital in civil engineering.

• Key Concepts: RL & Datum – Definitions of Reduced Level, Datum, and Benchmarks.

• Operating Levelling Instruments – Handling Auto Level and Tilting Level.

🛰️ Part 5: Modern Technologies

• Remote Sensing – Information on INSAT and IRS Series satellites.

• GIS & LIS Systems – Geographic data management and functionality.

• Laser Scanning – Advanced application and control.

• Geoid & Ellipsoid – Understanding the mathematical shape of the Earth.

📝 Part 6: Practice & Quizzes (MCQs)

• Surveying Quiz 1 (01-25) – GPS, Remote Sensing, and Photogrammetry.

• Surveying Quiz 2 (26-50) – Ranging, EDM, and Tacheometry.

• Surveying Quiz 3 (51-75) – Contouring and HI Method Levelling.

• Surveying Quiz 4 (76-100) – Transition Curves and Bowditch Rule.

• Surveying Quiz 5 (101-125) –  Plane table and Compass

• Surveying Quiz 6 (125-150) –  Theodolite Surveying and Levelling

• Surveying Quiz 7 (151-175) –  Tacheometry, Curves, Modern Surveying Instruments (EDM/GPS)

• Surveying Quiz 8 (175-200) –  Area & Volume Calculation, Minor Instruments

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📚 Quick Revision Resources

• Surveying Top 1-100 One-Liners

• Surveying Advanced (101-200) One-Liners

• Surveying Master Class (Part 1)

• Surveying Master Class (Part 2)

• Quick Revision Guide

• Quick Surveying Formulas

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Surveying IS Codes with Latest Revision Years

1. General Surveying & Instruments

• IS 1491:1959 – Specification for Prismatic Compass (Liquid and Non-liquid).

• IS 1963:1981 – Specification for Bubbles for Surveying Instruments.

• IS 2988:1995 – Glossary of Terms Relating to Surveying Instruments.

• IS 1634:1992 – Code of Practice for Design and Construction of Storage for Surveying Instruments.

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2. Chain and Tape Surveying

• IS 1492:1970 – Specification for Metric Surveying Chains.

• IS 1269 (Part 1):1997 – Material and Construction of Steel Tapes.

• IS 1269 (Part 2):1997 – Woven Metallic and Glass Fibre Tapes.

• IS 1659:2006 – Specification for Invar Tapes for High Precision Measurement.

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3. Theodolite and Tacheometry

• IS 8002:1976 – Specification for Surveying Chain Vertical Vernier Theodolite.

• IS 8330:1976 – Specification for Tilting Levels (Optical).

• IS 8636:1977 – Specification for Tacheometers.

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4. Leveling and Contouring

• IS 9128:1992 – Specification for Tilting Levels.

• IS 9573:1980 – Specification for Automatic Levels.

• IS 1779:1961 – Specification for 4-metre Leveling Staff (Folding Type).

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5. Modern Surveying (Total Station & GPS)

• IS 16481:2016 – Guidelines for Accuracy and Testing of Total Stations.

• IS 14855:2000 – Terminology and Concepts for GIS and Remote Sensing.

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6. Measurement of Building Works

• IS 1200 (Part 27):1992 – Method of Measurement of Building and Civil Engineering Works (Earthwork & Surveying).