Measurement of Distance and Direction in Surveying – [JKSSB Civil JE Complete Guide] -

📌 Introduction: Why it Matters

In Civil Engineering, surveying is the foundation of every infrastructure project. Whether constructing a road, canal, building, or bridge — accurate measurement of distances and directions is the first step.

For JKSSB Civil JE aspirants, understanding how measurements are taken, which tools are used, and the types of errors/corrections is essential, as 3–6 questions are typically asked from this section.

🧭 Two Key Measurements in Surveying

Surveying measurements are classified into two main types:

1️⃣ Linear Measurement (Distance)

Determines how far apart two points are on the ground.

2️⃣ Angular/Directional Measurement

Determines in which direction one point lies relative to another, using reference directions like North.

📐 I. Measurement of Distance (Linear Measurement)

🔹 What is Linear Measurement?

It is the determination of the straight-line distance between two points on the Earth’s surface. It can be:

Horizontal distance (most common)
Vertical distance (for elevation)
Slope distance (on hills or ramps)

📏 Methods of Measuring Distance

A. Direct Methods

Measured physically using tools.

Tool	Used For	Accuracy
Chain	Flat terrain, small projects	Low
Tape (Steel/Metallic)	Precise short measurements	Medium to high
Pacing	Rough, approximate measurement	Very low

✅ Best used when terrain is open and accessible.

B. Indirect Methods

Used when terrain is difficult or direct access is not possible.

Tool	Principle	Use Case
Tacheometer	Uses optics + angles	Hilly terrain, inaccessible zones
GPS	Satellite-based position fixing	Modern surveying
EDM	Electromagnetic wave propagation	Long/high-precision surveys

🧮 Tacheometric Distance Formula

Tacheometry calculates distance using the equation: D=K⋅S+CD = K \cdot S + CD=K⋅S+C

Where:

DDD = horizontal distance
SSS = staff intercept
KKK = multiplying constant (usually 100)
CCC = additive constant (instrument-specific)

✅ JKSSB Insight: Know this formula — it’s a frequently asked MCQ.

📉 Corrections in Linear Measurement

Field measurements are rarely perfect. Apply corrections to improve accuracy:

Type of Correction	Cause	Formula (Basic)
Temperature	Expansion/contraction of tape	CT=α(T−T0)⋅LC_T = \alpha (T – T_0) \cdot LCT=α(T−T0)⋅L
Slope	Difference in elevation	H=Lcos⁡θH = L \cos \thetaH=Lcosθ
Pull (Tension)	Extra/less force applied	CP=(P−P0)LAEC_P = \frac{(P – P_0)L}{AE}CP=AE(P−P0)L
Sag	Tape sags under weight	Negative correction

✅ Learn basic correction formulas. Often, 1 numerical MCQ is asked.

📊 Practical Example

Problem: A chain of 20 m length is used to measure a line. If the measured length is 200 m on a slope of 5°, find the horizontal length.

Solution:
Use Lh=Lcos⁡θL_h = L \cos \thetaLh=Lcosθ Lh=200⋅cos⁡5∘=200⋅0.9962=199.24 mL_h = 200 \cdot \cos 5^\circ = 200 \cdot 0.9962 = 199.24 \, \text{m}Lh=200⋅cos5∘=200⋅0.9962=199.24m

🧭 II. Measurement of Direction (Angular Measurement)

Direction defines where a point lies with respect to another, using a reference such as magnetic north, true north, or a meridian.

🔹 Types of Directional Systems

System	Reference	Used In
Magnetic Meridian	Magnetic North	Compass Survey
True Meridian	Geographic North	Theodolite
Arbitrary Meridian	Chosen reference	Plane Table Survey

📐 Types of Bearings

1. Whole Circle Bearing (WCB)

Measured clockwise from north → 0° to 360°

Example: East = 90°, South = 180°, West = 270°

2. Reduced or Quadrantal Bearing (QB)

Measured from N/S toward E/W → max value = 90°

Format: N 30° E, S 45° W, etc.

📌 WCB = QB Conversion may be asked.

🔁 Fore Bearing (FB) & Back Bearing (BB)

FB: In direction of survey line
BB: In opposite direction

Formula:
If FB < 180°, then BB = FB + 180°
If FB > 180°, then BB = FB – 180°

📏 Instruments Used for Measuring Direction

🧭 Compass

Prismatic Compass (WCB system)
Surveyor’s Compass (QB system)
Used in compass traversing
Least count: 0.5°

🔩 Theodolite

Measures both horizontal and vertical angles
Highly accurate
Used for advanced angular surveying, triangulation

🛰️ Total Station

Combines EDM + Theodolite + Data Logger
Records angles, distances, and coordinates digitally
Used in modern and large-scale projects

📊 Practical Example

Problem: A line has a FB of 70°. Find the BB.

Solution:
Since FB < 180°, BB=70∘+180∘=250∘BB = 70^\circ + 180^\circ = 250^\circBB=70∘+180∘=250∘

🔄 Comparison Table: Distance vs Direction

Feature	Distance	Direction
Quantity Type	Scalar	Angular
Measured Using	Chain, Tape, EDM	Compass, Theodolite
Units	Meters, feet	Degrees, radians
Errors	Slope, temperature	Magnetic declination, instrumental error

🧠 Last-Minute Revision Tips

Focus on difference between WCB and QB
Revise formulas related to corrections and tacheometry
Practice problems based on bearings and back bearing
Learn instrument names and their uses
Refer to previous year JKSSB papers

✅ Conclusion

Understanding the measurement of distance and direction is not only fundamental for fieldwork but also highly scoring in JKSSB exams. Master the instruments, formulas, and practical problems to confidently answer any related question in the exam.